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Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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  Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Baolin Wang <baolin.wang@linaro.org> - 2016-08-29 11:10 +0200
    Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <nfbrown@novell.com> - 2016-09-06 07:50 +0200
      Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation Felipe Balbi <balbi@kernel.org> - 2016-09-06 09:50 +0200
      Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Baolin Wang <baolin.wang@linaro.org> - 2016-09-08 09:00 +0200
        Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-08 09:40 +0200
          Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Baolin Wang <baolin.wang@linaro.org> - 2016-09-08 10:20 +0200
            Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-09 01:20 +0200
              Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Baolin Wang <baolin.wang@linaro.org> - 2016-09-09 08:50 +0200
                Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-09 23:20 +0200
                  Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Baolin Wang <baolin.wang@linaro.org> - 2016-09-18 11:40 +0200
              Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-09 13:10 +0200
                Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-10 00:00 +0200
                  Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-12 14:30 +0200
                    Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-12 15:30 +0200
                      Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-12 17:30 +0200
                        Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-13 10:10 +0200
                          Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-14 13:20 +0200
                            Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-14 16:20 +0200
                              Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-14 17:00 +0200
                                Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation NeilBrown <neilb@suse.com> - 2016-09-14 20:00 +0200
                                  Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Mark Brown <broonie@kernel.org> - 2016-09-14 20:10 +0200
                          Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the  usb gadget power negotation Pavel Machek <pavel@ucw.cz> - 2016-09-15 12:40 +0200

Page 1 of 2  [1] 2  Next page →

#1471658 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

Hi Felipe,

On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@linaro.org> wrote:
> Hi Felipe,
>
> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@linaro.org> wrote:
>> Currently the Linux kernel does not provide any standard integration of this
>> feature that integrates the USB subsystem with the system power regulation
>> provided by PMICs meaning that either vendors must add this in their kernels
>> or USB gadget devices based on Linux (such as mobile phones) may not behave
>> as they should. Thus provide a standard framework for doing this in kernel.
>>
>> Now introduce one user with wm831x_power to support and test the usb charger,
>> which is pending testing. Moreover there may be other potential users will use
>> it in future.
>
> Could you please apply this patchset into your 'next' branch if you
> have no comments about it? Thank you.

Since there are no other comments about this patchset for a long time,
could you please apply this patchset? Thanks.

>
>>
>> CHanges since v15:
>>  - Add charger state checking to avoid sending out duplicate notifies to users.
>>  - Add one work to notify power users the current has been changed.
>>
>> Changes since v14:
>>  - Add kernel documentation for struct usb_cahrger.
>>  - Remove some redundant WARN() functions.
>>
>> Changes since v13:
>>  - Remove the charger checking in usb_gadget_vbus_draw() function.
>>  - Rename some functions in charger.c file.
>>  - Rebase on git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git tags/usb-for-v4.8
>>
>> Changes since v12:
>>  - Remove the class and device things.
>>  - Link usb charger to udc-core.ko.
>>  - Create one "charger" subdirectory which holds all charger-related attributes.
>>
>> Changes since v11:
>>  - Reviewed and tested by Li Jun.
>>
>> Changes since v10:
>>  - Introduce usb_charger_get_state() function to check charger state.
>>  - Remove the mutex lock in usb_charger_set_cur_limit_by_type() function
>>  in case will be issued in atomic context.
>>
>> Baolin Wang (4):
>>   usb: gadget: Introduce the usb charger framework
>>   usb: gadget: Support for the usb charger framework
>>   usb: gadget: Integrate with the usb gadget supporting for usb charger
>>   power: wm831x_power: Support USB charger current limit management
>>
>>  drivers/power/wm831x_power.c     |   69 ++++
>>  drivers/usb/gadget/Kconfig       |    8 +
>>  drivers/usb/gadget/udc/Makefile  |    1 +
>>  drivers/usb/gadget/udc/charger.c |  780 ++++++++++++++++++++++++++++++++++++++
>>  drivers/usb/gadget/udc/core.c    |   17 +
>>  include/linux/mfd/wm831x/pdata.h |    3 +
>>  include/linux/usb/charger.h      |  186 +++++++++
>>  include/linux/usb/gadget.h       |    3 +
>>  include/uapi/linux/usb/charger.h |   31 ++
>>  9 files changed, 1098 insertions(+)
>>  create mode 100644 drivers/usb/gadget/udc/charger.c
>>  create mode 100644 include/linux/usb/charger.h
>>  create mode 100644 include/uapi/linux/usb/charger.h
>>
>> --
>> 1.7.9.5
>>
>
>
>
> --
> Baolin.wang
> Best Regards



-- 
Baolin.wang
Best Regards

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#1477085 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Mon, Aug 29 2016, Baolin Wang wrote:

> Hi Felipe,
>
> On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@linaro.org> wrote:
>> Hi Felipe,
>>
>> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@linaro.org> wrote:
>>> Currently the Linux kernel does not provide any standard integration of this
>>> feature that integrates the USB subsystem with the system power regulation
>>> provided by PMICs meaning that either vendors must add this in their kernels
>>> or USB gadget devices based on Linux (such as mobile phones) may not behave
>>> as they should. Thus provide a standard framework for doing this in kernel.
>>>
>>> Now introduce one user with wm831x_power to support and test the usb charger,
>>> which is pending testing. Moreover there may be other potential users will use
>>> it in future.
>>
>> Could you please apply this patchset into your 'next' branch if you
>> have no comments about it? Thank you.
>
> Since there are no other comments about this patchset for a long time,
> could you please apply this patchset? Thanks.

Sorry, I should have replied earlier.  Tim Bird mentioned on the
ksummit-discuss list that there was a frustration with this not making
progress so I decided to contribute what I could now.

I think this patch set is attempting to address an important problem
that needs solving.  However I think it gets some key aspects wrong.
Maybe they can get fixed up after the patchset is upstream, maybe they
should be fixed first - I have no strong opinion on that.

My main complaints involve the detection and handling of the different
charger types - DCP, CDP, ACA etc.
The big-picture requirement here that the PHY will detect the physical
properties of the cable (e.g. resistance to ground on ID) and determine
the type of charger expected.  This information must be communicated to
the PMIC "power_supply" device so it can regulate the power being drawn
through the cable.

The first problem is that there are two different ways that the
distinction between DCP, CDP, ACA etc can be represented in Linux.  They
are cable types in the 'extcon' subsystem, and they are power_supply
types in the 'power_supply' subsystem.  This duplication is confusing.
It is not caused by your patch set, but I believe your patchset needs to
work with the duplication and I think it does so poorly.

In my mind, the power_supply should *not* know about this distinction at
all (except possibly as an advisor attribute simiarly to the current
battery technology attribute).  The other types it knows of are "AC",
"USB", and "BATTERY".  The contrast between these is quite different
From the contrast between DCP, CDP, ACA, which, from the perspective of
the power supply, are almost irrelevant.  Your patchset effectively
examines the power_supply_type of one power_supply, and communicates it
to another.  It isn't clear to me how the first power_supply gets the
information, or what the relationship between the two power_supplies is
meant to be.

It makes much more sense, to me, to utilized the knowledge of this
distinction that extcon provides.  A usb PHY can register an extcon,
declare the sorts of cables that it can detect, and tell the extcon as
cables appear or disappear.  The PMIC power_supply can then register with
that extcon for events and can find out when a cable is attached, and
what sort of cable.
Your usb-charging framework would be well placed to help the
power_supply to find the correct extcon, and possibly even to handle the
registration for events.

Your framework does currently register with extcon, but only listens for
EXTCON_USB cables.  I don't think that cable type is (reliably) reported
when a DCP (for example) is plugged in.

Here there is another problem that is not of your making, but still
needs fixing.  Extcon declares a number of cable types like:

/* USB external connector */
#define EXTCON_USB              1
#define EXTCON_USB_HOST         2

/* Charging external connector */
#define EXTCON_CHG_USB_SDP      5       /* Standard Downstream Port */
#define EXTCON_CHG_USB_DCP      6       /* Dedicated Charging Port */
#define EXTCON_CHG_USB_CDP      7       /* Charging Downstream Port */
#define EXTCON_CHG_USB_ACA      8       /* Accessory Charger Adapter */
#define EXTCON_CHG_USB_FAST     9
#define EXTCON_CHG_USB_SLOW     10

However it doesn't define what those mean, so we are left to guess.
They each correspond to bits in a bitmap, so a cable can have multiple types.
I think the best interpretation is that:

 EXTCON_USB means that the cable carries USB data from a host.
 EXTCON_USB_HOST means that that cable carries USB data to a host.
 EXTCON_CHG_* means that power is available as described in the
 standards.
 (what EXTCON_CHG_USB_FAST and EXTCON_CHG_USB_SLOW mean is not at all
 clear).

There is some support for this in the code, but it is not universally
acknowledged.  For a USB charging framework to be genuinely useful, it
must (I think) make sure this issue gets clarified, and the various
cable types used properly.

Once the cable/charger type has been determined, the PMIC power_supply
needs to use this information.  Your current patches make use of this
information in ways that are wrong in two respects.

Firstly, you have made the current limit associated with each cable type
configurable (__usb_charger_set_cur_limit_by_type).   This is nonsense.
The standard (e.g. BC-1.2) declares what the current limits are.  There
is no reason for those not to be hard coded.

Secondly, you treat each charger type as having a single "cur_limit" and
utilize that limit by telling the PMIC to draw that much current.
Again, this is inconsistent with the specification.
BC-1.2 defines, for each charger type, a minimum and maximum current
level.
The minimum should always be available.   Attempting to draw more than
that (but less that the max) might work or might cause the charger
to shut down, but you can be sure that the charger will respond to the
increased load by first reducing the voltage, and will not shut down
until the voltage has dropped below 2V.
If you try to draw more current than the maximum, then the charger might
shut down before the voltage drops below 2V.

Given this understanding of the current available from the charger,
there are two approaches the PMIC might take.
1/ if the PMIC is able to exercise fine control over the current it
  draws, and if it can monitor the voltage on the charger, then it
  could gradually increase the power being requested until the voltage
  drops below some threshold (e.g. 4.75V), and then (probably) back off
  a little.  It should only increase at most up to the maximum, even if
  the voltage remains high.  It should probably start at zero rather
  than at the minimum.  This allows for lossage elsewhere.

2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine
   control of the current requested, then it should request only the
   minimum available current.  Any more is not safe.

So your USB charging framework should communicate the MIN and MAX as
specified in the standard, and allow the PMIC to use that information as
appropriate.
A library routine to support the incremental increase in current drain
would probably be appreciated by PMIC driver writers.


A more details discussion of this problem-space can be found at
   https://lwn.net/Articles/693027/
and an analysis of the functionality currently available in the kernel
(which adds a number of specifics to the above) can be found at
   https://lwn.net/Articles/694062/

NeilBrown

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#1477133 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Hi,

NeilBrown <nfbrown@novell.com> writes:
> Firstly, you have made the current limit associated with each cable type
> configurable (__usb_charger_set_cur_limit_by_type).   This is nonsense.
> The standard (e.g. BC-1.2) declares what the current limits are.  There
> is no reason for those not to be hard coded.

I had raised the same concern WRT configuration current limits.

> Secondly, you treat each charger type as having a single "cur_limit" and
> utilize that limit by telling the PMIC to draw that much current.
> Again, this is inconsistent with the specification.
> BC-1.2 defines, for each charger type, a minimum and maximum current
> level.
> The minimum should always be available.   Attempting to draw more than
> that (but less that the max) might work or might cause the charger
> to shut down, but you can be sure that the charger will respond to the
> increased load by first reducing the voltage, and will not shut down
> until the voltage has dropped below 2V.
> If you try to draw more current than the maximum, then the charger might
> shut down before the voltage drops below 2V.

Very well put :-)

> Given this understanding of the current available from the charger,
> there are two approaches the PMIC might take.
> 1/ if the PMIC is able to exercise fine control over the current it
>   draws, and if it can monitor the voltage on the charger, then it
>   could gradually increase the power being requested until the voltage
>   drops below some threshold (e.g. 4.75V), and then (probably) back off
>   a little.  It should only increase at most up to the maximum, even if
>   the voltage remains high.  It should probably start at zero rather
>   than at the minimum.  This allows for lossage elsewhere.

That's what most charging control SW I've seen in the past ends up
doing. Correct

> 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine
>    control of the current requested, then it should request only the
>    minimum available current.  Any more is not safe.

correct

-- 
balbi

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#1478822

Hi Neil,

On 6 September 2016 at 13:40, NeilBrown <nfbrown@novell.com> wrote:
> On Mon, Aug 29 2016, Baolin Wang wrote:
>
>> Hi Felipe,
>>
>> On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@linaro.org> wrote:
>>> Hi Felipe,
>>>
>>> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@linaro.org> wrote:
>>>> Currently the Linux kernel does not provide any standard integration of this
>>>> feature that integrates the USB subsystem with the system power regulation
>>>> provided by PMICs meaning that either vendors must add this in their kernels
>>>> or USB gadget devices based on Linux (such as mobile phones) may not behave
>>>> as they should. Thus provide a standard framework for doing this in kernel.
>>>>
>>>> Now introduce one user with wm831x_power to support and test the usb charger,
>>>> which is pending testing. Moreover there may be other potential users will use
>>>> it in future.
>>>
>>> Could you please apply this patchset into your 'next' branch if you
>>> have no comments about it? Thank you.
>>
>> Since there are no other comments about this patchset for a long time,
>> could you please apply this patchset? Thanks.
>

Sorry for the late reply.

> Sorry, I should have replied earlier.  Tim Bird mentioned on the
> ksummit-discuss list that there was a frustration with this not making
> progress so I decided to contribute what I could now.
>
> I think this patch set is attempting to address an important problem
> that needs solving.  However I think it gets some key aspects wrong.
> Maybe they can get fixed up after the patchset is upstream, maybe they
> should be fixed first - I have no strong opinion on that.
>
> My main complaints involve the detection and handling of the different
> charger types - DCP, CDP, ACA etc.
> The big-picture requirement here that the PHY will detect the physical
> properties of the cable (e.g. resistance to ground on ID) and determine
> the type of charger expected.  This information must be communicated to
> the PMIC "power_supply" device so it can regulate the power being drawn
> through the cable.
>
> The first problem is that there are two different ways that the
> distinction between DCP, CDP, ACA etc can be represented in Linux.  They
> are cable types in the 'extcon' subsystem, and they are power_supply
> types in the 'power_supply' subsystem.  This duplication is confusing.
> It is not caused by your patch set, but I believe your patchset needs to
> work with the duplication and I think it does so poorly.

Now the usb charger will not get charger type from 'extcon' subsystem,
we get the charger type from 'power_supply' and calllback
'get_charger_type' for users.

>
> In my mind, the power_supply should *not* know about this distinction at
> all (except possibly as an advisor attribute simiarly to the current
> battery technology attribute).  The other types it knows of are "AC",
> "USB", and "BATTERY".  The contrast between these is quite different
> From the contrast between DCP, CDP, ACA, which, from the perspective of
> the power supply, are almost irrelevant.  Your patchset effectively
> examines the power_supply_type of one power_supply, and communicates it
> to another.  It isn't clear to me how the first power_supply gets the
> information, or what the relationship between the two power_supplies is
> meant to be.

We just get the charger type from the power supply which can get the
charger type from register or something else, and the usb charger did
nothing for this power supply. In some platform, the charger type is
get in power supply driver, thus we should link this power supply to
get the charger type when USB cable is plugin. If you don't get
charger type from power supply driver, then it does not need to link
this power supply phandle.

>
> It makes much more sense, to me, to utilized the knowledge of this
> distinction that extcon provides.  A usb PHY can register an extcon,
> declare the sorts of cables that it can detect, and tell the extcon as
> cables appear or disappear.  The PMIC power_supply can then register with
> that extcon for events and can find out when a cable is attached, and
> what sort of cable.
> Your usb-charging framework would be well placed to help the
> power_supply to find the correct extcon, and possibly even to handle the
> registration for events.
>
> Your framework does currently register with extcon, but only listens for
> EXTCON_USB cables.  I don't think that cable type is (reliably) reported
> when a DCP (for example) is plugged in.

Here we just listen the plugin/out events from extcon, if one cable
plugin it will report to usb charger.

>
> Here there is another problem that is not of your making, but still
> needs fixing.  Extcon declares a number of cable types like:
>
> /* USB external connector */
> #define EXTCON_USB              1
> #define EXTCON_USB_HOST         2
>
> /* Charging external connector */
> #define EXTCON_CHG_USB_SDP      5       /* Standard Downstream Port */
> #define EXTCON_CHG_USB_DCP      6       /* Dedicated Charging Port */
> #define EXTCON_CHG_USB_CDP      7       /* Charging Downstream Port */
> #define EXTCON_CHG_USB_ACA      8       /* Accessory Charger Adapter */
> #define EXTCON_CHG_USB_FAST     9
> #define EXTCON_CHG_USB_SLOW     10
>
> However it doesn't define what those mean, so we are left to guess.
> They each correspond to bits in a bitmap, so a cable can have multiple types.
> I think the best interpretation is that:
>
>  EXTCON_USB means that the cable carries USB data from a host.
>  EXTCON_USB_HOST means that that cable carries USB data to a host.
>  EXTCON_CHG_* means that power is available as described in the
>  standards.
>  (what EXTCON_CHG_USB_FAST and EXTCON_CHG_USB_SLOW mean is not at all
>  clear).
>
> There is some support for this in the code, but it is not universally
> acknowledged.  For a USB charging framework to be genuinely useful, it
> must (I think) make sure this issue gets clarified, and the various
> cable types used properly.

Here I agree with you, now the usb charger does not listen the charger
type from extcon which need to be fixed.

>
> Once the cable/charger type has been determined, the PMIC power_supply
> needs to use this information.  Your current patches make use of this
> information in ways that are wrong in two respects.
>
> Firstly, you have made the current limit associated with each cable type
> configurable (__usb_charger_set_cur_limit_by_type).   This is nonsense.
> The standard (e.g. BC-1.2) declares what the current limits are.  There
> is no reason for those not to be hard coded.

Yes, but you must think about some special cases on some platforms.
Users may need to change the current in some situations, thus we
should export one API for users to change the current. (I think you
misunderstand the current limit here, that is the current for power
driver  to draw).

>
> Secondly, you treat each charger type as having a single "cur_limit" and
> utilize that limit by telling the PMIC to draw that much current.

This "cur_limit" is set by user or USB configuration what they want,
usb charger just tells the power driver how much current need to draw.

> Again, this is inconsistent with the specification.
> BC-1.2 defines, for each charger type, a minimum and maximum current
> level.
> The minimum should always be available.   Attempting to draw more than
> that (but less that the max) might work or might cause the charger
> to shut down, but you can be sure that the charger will respond to the
> increased load by first reducing the voltage, and will not shut down
> until the voltage has dropped below 2V.
> If you try to draw more current than the maximum, then the charger might
> shut down before the voltage drops below 2V.
>
> Given this understanding of the current available from the charger,
> there are two approaches the PMIC might take.
> 1/ if the PMIC is able to exercise fine control over the current it
>   draws, and if it can monitor the voltage on the charger, then it
>   could gradually increase the power being requested until the voltage
>   drops below some threshold (e.g. 4.75V), and then (probably) back off
>   a little.  It should only increase at most up to the maximum, even if
>   the voltage remains high.  It should probably start at zero rather
>   than at the minimum.  This allows for lossage elsewhere.
>
> 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine
>    control of the current requested, then it should request only the
>    minimum available current.  Any more is not safe.

Make sense.

>
> So your USB charging framework should communicate the MIN and MAX as
> specified in the standard, and allow the PMIC to use that information as
> appropriate.
> A library routine to support the incremental increase in current drain
> would probably be appreciated by PMIC driver writers.

I should say again, the current is set by user or USB configuration
what they want, USB charger just tells the power driver how much
current need to draw. But we can add some checking if the setting
current is in the right range.

Thanks for your comments.

>
>
> A more details discussion of this problem-space can be found at
>    https://lwn.net/Articles/693027/
> and an analysis of the functionality currently available in the kernel
> (which adds a number of specifics to the above) can be found at
>    https://lwn.net/Articles/694062/
>
> NeilBrown
>
>



-- 
Baolin.wang
Best Regards

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#1478866 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Thu, Sep 08 2016, Baolin Wang wrote:

> Hi Neil,
>
> On 6 September 2016 at 13:40, NeilBrown <nfbrown@novell.com> wrote:
>> On Mon, Aug 29 2016, Baolin Wang wrote:
>>
>>> Hi Felipe,
>>>
>>> On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@linaro.org> wrote:
>>>> Hi Felipe,
>>>>
>>>> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@linaro.org> wrote:
>>>>> Currently the Linux kernel does not provide any standard integration of this
>>>>> feature that integrates the USB subsystem with the system power regulation
>>>>> provided by PMICs meaning that either vendors must add this in their kernels
>>>>> or USB gadget devices based on Linux (such as mobile phones) may not behave
>>>>> as they should. Thus provide a standard framework for doing this in kernel.
>>>>>
>>>>> Now introduce one user with wm831x_power to support and test the usb charger,
>>>>> which is pending testing. Moreover there may be other potential users will use
>>>>> it in future.
>>>>
>>>> Could you please apply this patchset into your 'next' branch if you
>>>> have no comments about it? Thank you.
>>>
>>> Since there are no other comments about this patchset for a long time,
>>> could you please apply this patchset? Thanks.
>>
>
> Sorry for the late reply.
>
>> Sorry, I should have replied earlier.  Tim Bird mentioned on the
>> ksummit-discuss list that there was a frustration with this not making
>> progress so I decided to contribute what I could now.
>>
>> I think this patch set is attempting to address an important problem
>> that needs solving.  However I think it gets some key aspects wrong.
>> Maybe they can get fixed up after the patchset is upstream, maybe they
>> should be fixed first - I have no strong opinion on that.
>>
>> My main complaints involve the detection and handling of the different
>> charger types - DCP, CDP, ACA etc.
>> The big-picture requirement here that the PHY will detect the physical
>> properties of the cable (e.g. resistance to ground on ID) and determine
>> the type of charger expected.  This information must be communicated to
>> the PMIC "power_supply" device so it can regulate the power being drawn
>> through the cable.
>>
>> The first problem is that there are two different ways that the
>> distinction between DCP, CDP, ACA etc can be represented in Linux.  They
>> are cable types in the 'extcon' subsystem, and they are power_supply
>> types in the 'power_supply' subsystem.  This duplication is confusing.
>> It is not caused by your patch set, but I believe your patchset needs to
>> work with the duplication and I think it does so poorly.
>
> Now the usb charger will not get charger type from 'extcon' subsystem,
> we get the charger type from 'power_supply' and calllback
> 'get_charger_type' for users.

I understand this.  I think it is wrong because, in general, the
power_supply doesn't know what the charger_type is (it might know it is
USB, but most don't know which sort of USB).  The PHY knows that, not
the power_supply.


>
>>
>> In my mind, the power_supply should *not* know about this distinction at
>> all (except possibly as an advisor attribute simiarly to the current
>> battery technology attribute).  The other types it knows of are "AC",
>> "USB", and "BATTERY".  The contrast between these is quite different
>> From the contrast between DCP, CDP, ACA, which, from the perspective of
>> the power supply, are almost irrelevant.  Your patchset effectively
>> examines the power_supply_type of one power_supply, and communicates it
>> to another.  It isn't clear to me how the first power_supply gets the
>> information, or what the relationship between the two power_supplies is
>> meant to be.
>
> We just get the charger type from the power supply which can get the
> charger type from register or something else,

But that register would be part of the PHY, not part of the charger.
Having the power_supply driver reading the PHY register might work for
some hardware, but is not a general solution.


>                                                and the usb charger did
> nothing for this power supply. In some platform, the charger type is
> get in power supply driver, thus we should link this power supply to
> get the charger type when USB cable is plugin. If you don't get
> charger type from power supply driver, then it does not need to link
> this power supply phandle.
>
>>
>> It makes much more sense, to me, to utilized the knowledge of this
>> distinction that extcon provides.  A usb PHY can register an extcon,
>> declare the sorts of cables that it can detect, and tell the extcon as
>> cables appear or disappear.  The PMIC power_supply can then register with
>> that extcon for events and can find out when a cable is attached, and
>> what sort of cable.
>> Your usb-charging framework would be well placed to help the
>> power_supply to find the correct extcon, and possibly even to handle the
>> registration for events.
>>
>> Your framework does currently register with extcon, but only listens for
>> EXTCON_USB cables.  I don't think that cable type is (reliably) reported
>> when a DCP (for example) is plugged in.
>
> Here we just listen the plugin/out events from extcon, if one cable
> plugin it will report to usb charger.

As far as I can tell there are no generic "plugin/out events from extcon".
There are only events for a specific cable being plugged or unplugged.
So you need to listed for each different type of cable that you are
interested in.

If it detects a "EXTCON_CHG_USB_ACA plugged" event, then it makes sense
to use that event to tell the power supply that the current profile for
an ACA is available.


>
>>
>> Here there is another problem that is not of your making, but still
>> needs fixing.  Extcon declares a number of cable types like:
>>
>> /* USB external connector */
>> #define EXTCON_USB              1
>> #define EXTCON_USB_HOST         2
>>
>> /* Charging external connector */
>> #define EXTCON_CHG_USB_SDP      5       /* Standard Downstream Port */
>> #define EXTCON_CHG_USB_DCP      6       /* Dedicated Charging Port */
>> #define EXTCON_CHG_USB_CDP      7       /* Charging Downstream Port */
>> #define EXTCON_CHG_USB_ACA      8       /* Accessory Charger Adapter */
>> #define EXTCON_CHG_USB_FAST     9
>> #define EXTCON_CHG_USB_SLOW     10
>>
>> However it doesn't define what those mean, so we are left to guess.
>> They each correspond to bits in a bitmap, so a cable can have multiple types.
>> I think the best interpretation is that:
>>
>>  EXTCON_USB means that the cable carries USB data from a host.
>>  EXTCON_USB_HOST means that that cable carries USB data to a host.
>>  EXTCON_CHG_* means that power is available as described in the
>>  standards.
>>  (what EXTCON_CHG_USB_FAST and EXTCON_CHG_USB_SLOW mean is not at all
>>  clear).
>>
>> There is some support for this in the code, but it is not universally
>> acknowledged.  For a USB charging framework to be genuinely useful, it
>> must (I think) make sure this issue gets clarified, and the various
>> cable types used properly.
>
> Here I agree with you, now the usb charger does not listen the charger
> type from extcon which need to be fixed.
>
>>
>> Once the cable/charger type has been determined, the PMIC power_supply
>> needs to use this information.  Your current patches make use of this
>> information in ways that are wrong in two respects.
>>
>> Firstly, you have made the current limit associated with each cable type
>> configurable (__usb_charger_set_cur_limit_by_type).   This is nonsense.
>> The standard (e.g. BC-1.2) declares what the current limits are.  There
>> is no reason for those not to be hard coded.
>
> Yes, but you must think about some special cases on some platforms.
> Users may need to change the current in some situations, thus we
> should export one API for users to change the current. (I think you
> misunderstand the current limit here, that is the current for power
> driver  to draw).

Can you be specific about these "special cases" please?
I cannot think of any.

And what sort of "user" might use that API?  I don't think having an app
on your phone that allows you to set the max-current would be a good
idea, so you must be thinking of some other sort of user.

>
>>
>> Secondly, you treat each charger type as having a single "cur_limit" and
>> utilize that limit by telling the PMIC to draw that much current.
>
> This "cur_limit" is set by user or USB configuration what they want,
> usb charger just tells the power driver how much current need to draw.

You don't tell the power driver "how much current it needs to draw".
You tell it "how much current it is safe to draw".

A power driver cannot draw current that isn't available, and it cannot
draw current that the system as a whole has no use for.
The task of the power driver is to make sure the system doesn't draw
more power than is available, else the voltage will drop and the power
supply might shut off.

>
>> Again, this is inconsistent with the specification.
>> BC-1.2 defines, for each charger type, a minimum and maximum current
>> level.
>> The minimum should always be available.   Attempting to draw more than
>> that (but less that the max) might work or might cause the charger
>> to shut down, but you can be sure that the charger will respond to the
>> increased load by first reducing the voltage, and will not shut down
>> until the voltage has dropped below 2V.
>> If you try to draw more current than the maximum, then the charger might
>> shut down before the voltage drops below 2V.
>>
>> Given this understanding of the current available from the charger,
>> there are two approaches the PMIC might take.
>> 1/ if the PMIC is able to exercise fine control over the current it
>>   draws, and if it can monitor the voltage on the charger, then it
>>   could gradually increase the power being requested until the voltage
>>   drops below some threshold (e.g. 4.75V), and then (probably) back off
>>   a little.  It should only increase at most up to the maximum, even if
>>   the voltage remains high.  It should probably start at zero rather
>>   than at the minimum.  This allows for lossage elsewhere.
>>
>> 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine
>>    control of the current requested, then it should request only the
>>    minimum available current.  Any more is not safe.
>
> Make sense.
>
>>
>> So your USB charging framework should communicate the MIN and MAX as
>> specified in the standard, and allow the PMIC to use that information as
>> appropriate.
>> A library routine to support the incremental increase in current drain
>> would probably be appreciated by PMIC driver writers.
>
> I should say again, the current is set by user or USB configuration
> what they want, USB charger just tells the power driver how much
> current need to draw. But we can add some checking if the setting
> current is in the right range.

The USB configuration tells the Host how much power it needs.  If the
host enables the configuration, that implicitly say that much power is
available, so the power_driver can safely request it.  I'm mostly happy
wit that aspect of your patch set.

For a dedicated charger there is no USB configuration.  The electrical
properties of the cable provide some information about how the charger
will behave, but they only guarantee a minimum.  If you want to use more
than the minimum, you have to do so carefully and watch the voltage level.
You cannot sensible let the user tell you how much current the charger
can provide, because they'll probably get it wrong and the charger will
just shut down.

Thanks,
NeilBrown


>
> Thanks for your comments.
>
>>
>>
>> A more details discussion of this problem-space can be found at
>>    https://lwn.net/Articles/693027/
>> and an analysis of the functionality currently available in the kernel
>> (which adds a number of specifics to the above) can be found at
>>    https://lwn.net/Articles/694062/
>>
>> NeilBrown
>>
>>
>
>
>
> -- 
> Baolin.wang
> Best Regards

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#1478903

On 8 September 2016 at 15:31, NeilBrown <neilb@suse.com> wrote:
> On Thu, Sep 08 2016, Baolin Wang wrote:
>
>> Hi Neil,
>>
>> On 6 September 2016 at 13:40, NeilBrown <nfbrown@novell.com> wrote:
>>> On Mon, Aug 29 2016, Baolin Wang wrote:
>>>
>>>> Hi Felipe,
>>>>
>>>> On 11 August 2016 at 11:14, Baolin Wang <baolin.wang@linaro.org> wrote:
>>>>> Hi Felipe,
>>>>>
>>>>> On 1 August 2016 at 15:09, Baolin Wang <baolin.wang@linaro.org> wrote:
>>>>>> Currently the Linux kernel does not provide any standard integration of this
>>>>>> feature that integrates the USB subsystem with the system power regulation
>>>>>> provided by PMICs meaning that either vendors must add this in their kernels
>>>>>> or USB gadget devices based on Linux (such as mobile phones) may not behave
>>>>>> as they should. Thus provide a standard framework for doing this in kernel.
>>>>>>
>>>>>> Now introduce one user with wm831x_power to support and test the usb charger,
>>>>>> which is pending testing. Moreover there may be other potential users will use
>>>>>> it in future.
>>>>>
>>>>> Could you please apply this patchset into your 'next' branch if you
>>>>> have no comments about it? Thank you.
>>>>
>>>> Since there are no other comments about this patchset for a long time,
>>>> could you please apply this patchset? Thanks.
>>>
>>
>> Sorry for the late reply.
>>
>>> Sorry, I should have replied earlier.  Tim Bird mentioned on the
>>> ksummit-discuss list that there was a frustration with this not making
>>> progress so I decided to contribute what I could now.
>>>
>>> I think this patch set is attempting to address an important problem
>>> that needs solving.  However I think it gets some key aspects wrong.
>>> Maybe they can get fixed up after the patchset is upstream, maybe they
>>> should be fixed first - I have no strong opinion on that.
>>>
>>> My main complaints involve the detection and handling of the different
>>> charger types - DCP, CDP, ACA etc.
>>> The big-picture requirement here that the PHY will detect the physical
>>> properties of the cable (e.g. resistance to ground on ID) and determine
>>> the type of charger expected.  This information must be communicated to
>>> the PMIC "power_supply" device so it can regulate the power being drawn
>>> through the cable.
>>>
>>> The first problem is that there are two different ways that the
>>> distinction between DCP, CDP, ACA etc can be represented in Linux.  They
>>> are cable types in the 'extcon' subsystem, and they are power_supply
>>> types in the 'power_supply' subsystem.  This duplication is confusing.
>>> It is not caused by your patch set, but I believe your patchset needs to
>>> work with the duplication and I think it does so poorly.
>>
>> Now the usb charger will not get charger type from 'extcon' subsystem,
>> we get the charger type from 'power_supply' and calllback
>> 'get_charger_type' for users.
>
> I understand this.  I think it is wrong because, in general, the
> power_supply doesn't know what the charger_type is (it might know it is
> USB, but most don't know which sort of USB).  The PHY knows that, not
> the power_supply.

I don't think so. Now many platforms will detect the charger type by
PMIC hardware, and we can get the charger type by PMIC hardware
register. Then power supply driver can access the PMIC register to get
the charger type. Here USB charger just considers if the accessing the
PMIC register to get charger type is implemented in power supply, it
is optional depending on what your platform designed.

>>
>>>
>>> In my mind, the power_supply should *not* know about this distinction at
>>> all (except possibly as an advisor attribute simiarly to the current
>>> battery technology attribute).  The other types it knows of are "AC",
>>> "USB", and "BATTERY".  The contrast between these is quite different
>>> From the contrast between DCP, CDP, ACA, which, from the perspective of
>>> the power supply, are almost irrelevant.  Your patchset effectively
>>> examines the power_supply_type of one power_supply, and communicates it
>>> to another.  It isn't clear to me how the first power_supply gets the
>>> information, or what the relationship between the two power_supplies is
>>> meant to be.
>>
>> We just get the charger type from the power supply which can get the
>> charger type from register or something else,
>
> But that register would be part of the PHY, not part of the charger.
> Having the power_supply driver reading the PHY register might work for
> some hardware, but is not a general solution.

Not only PHY. Like I said, the charger type detection can be done by
PMIC hardware, power supply can get the charger type by accessing PMIC
registers.

>>                                                and the usb charger did
>> nothing for this power supply. In some platform, the charger type is
>> get in power supply driver, thus we should link this power supply to
>> get the charger type when USB cable is plugin. If you don't get
>> charger type from power supply driver, then it does not need to link
>> this power supply phandle.
>>
>>>
>>> It makes much more sense, to me, to utilized the knowledge of this
>>> distinction that extcon provides.  A usb PHY can register an extcon,
>>> declare the sorts of cables that it can detect, and tell the extcon as
>>> cables appear or disappear.  The PMIC power_supply can then register with
>>> that extcon for events and can find out when a cable is attached, and
>>> what sort of cable.
>>> Your usb-charging framework would be well placed to help the
>>> power_supply to find the correct extcon, and possibly even to handle the
>>> registration for events.
>>>
>>> Your framework does currently register with extcon, but only listens for
>>> EXTCON_USB cables.  I don't think that cable type is (reliably) reported
>>> when a DCP (for example) is plugged in.
>>
>> Here we just listen the plugin/out events from extcon, if one cable
>> plugin it will report to usb charger.
>
> As far as I can tell there are no generic "plugin/out events from extcon".
> There are only events for a specific cable being plugged or unplugged.

Yeah, that is what I meaning. Now we just listen plugged or unplugged
events from extcon.

> So you need to listed for each different type of cable that you are
> interested in.
>
> If it detects a "EXTCON_CHG_USB_ACA plugged" event, then it makes sense
> to use that event to tell the power supply that the current profile for
> an ACA is available.

Yes, I understand. Now USB charger doses not listen for each different
type of cable, which need to add.

>>
>>>
>>> Here there is another problem that is not of your making, but still
>>> needs fixing.  Extcon declares a number of cable types like:
>>>
>>> /* USB external connector */
>>> #define EXTCON_USB              1
>>> #define EXTCON_USB_HOST         2
>>>
>>> /* Charging external connector */
>>> #define EXTCON_CHG_USB_SDP      5       /* Standard Downstream Port */
>>> #define EXTCON_CHG_USB_DCP      6       /* Dedicated Charging Port */
>>> #define EXTCON_CHG_USB_CDP      7       /* Charging Downstream Port */
>>> #define EXTCON_CHG_USB_ACA      8       /* Accessory Charger Adapter */
>>> #define EXTCON_CHG_USB_FAST     9
>>> #define EXTCON_CHG_USB_SLOW     10
>>>
>>> However it doesn't define what those mean, so we are left to guess.
>>> They each correspond to bits in a bitmap, so a cable can have multiple types.
>>> I think the best interpretation is that:
>>>
>>>  EXTCON_USB means that the cable carries USB data from a host.
>>>  EXTCON_USB_HOST means that that cable carries USB data to a host.
>>>  EXTCON_CHG_* means that power is available as described in the
>>>  standards.
>>>  (what EXTCON_CHG_USB_FAST and EXTCON_CHG_USB_SLOW mean is not at all
>>>  clear).
>>>
>>> There is some support for this in the code, but it is not universally
>>> acknowledged.  For a USB charging framework to be genuinely useful, it
>>> must (I think) make sure this issue gets clarified, and the various
>>> cable types used properly.
>>
>> Here I agree with you, now the usb charger does not listen the charger
>> type from extcon which need to be fixed.
>>
>>>
>>> Once the cable/charger type has been determined, the PMIC power_supply
>>> needs to use this information.  Your current patches make use of this
>>> information in ways that are wrong in two respects.
>>>
>>> Firstly, you have made the current limit associated with each cable type
>>> configurable (__usb_charger_set_cur_limit_by_type).   This is nonsense.
>>> The standard (e.g. BC-1.2) declares what the current limits are.  There
>>> is no reason for those not to be hard coded.
>>
>> Yes, but you must think about some special cases on some platforms.
>> Users may need to change the current in some situations, thus we
>> should export one API for users to change the current. (I think you
>> misunderstand the current limit here, that is the current for power
>> driver  to draw).
>
> Can you be specific about these "special cases" please?
> I cannot think of any.

Suppose the USB configuration requests 100mA, then we should set the
USB charger current is 100mA by __usb_charger_set_cur_limit_by_type()
funtion, then notify this to power driver.

>
> And what sort of "user" might use that API?  I don't think having an app
> on your phone that allows you to set the max-current would be a good
> idea, so you must be thinking of some other sort of user.
>
>>
>>>
>>> Secondly, you treat each charger type as having a single "cur_limit" and
>>> utilize that limit by telling the PMIC to draw that much current.
>>
>> This "cur_limit" is set by user or USB configuration what they want,
>> usb charger just tells the power driver how much current need to draw.
>
> You don't tell the power driver "how much current it needs to draw".
> You tell it "how much current it is safe to draw".
>
> A power driver cannot draw current that isn't available, and it cannot
> draw current that the system as a whole has no use for.
> The task of the power driver is to make sure the system doesn't draw
> more power than is available, else the voltage will drop and the power
> supply might shut off.

How much current in USB charger is set by USB configuration or power
users, but yes, we can check if the current is available in USB
charger. If user set one unavailable we can ignore that setting.

>
>>
>>> Again, this is inconsistent with the specification.
>>> BC-1.2 defines, for each charger type, a minimum and maximum current
>>> level.
>>> The minimum should always be available.   Attempting to draw more than
>>> that (but less that the max) might work or might cause the charger
>>> to shut down, but you can be sure that the charger will respond to the
>>> increased load by first reducing the voltage, and will not shut down
>>> until the voltage has dropped below 2V.
>>> If you try to draw more current than the maximum, then the charger might
>>> shut down before the voltage drops below 2V.
>>>
>>> Given this understanding of the current available from the charger,
>>> there are two approaches the PMIC might take.
>>> 1/ if the PMIC is able to exercise fine control over the current it
>>>   draws, and if it can monitor the voltage on the charger, then it
>>>   could gradually increase the power being requested until the voltage
>>>   drops below some threshold (e.g. 4.75V), and then (probably) back off
>>>   a little.  It should only increase at most up to the maximum, even if
>>>   the voltage remains high.  It should probably start at zero rather
>>>   than at the minimum.  This allows for lossage elsewhere.
>>>
>>> 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine
>>>    control of the current requested, then it should request only the
>>>    minimum available current.  Any more is not safe.
>>
>> Make sense.
>>
>>>
>>> So your USB charging framework should communicate the MIN and MAX as
>>> specified in the standard, and allow the PMIC to use that information as
>>> appropriate.
>>> A library routine to support the incremental increase in current drain
>>> would probably be appreciated by PMIC driver writers.
>>
>> I should say again, the current is set by user or USB configuration
>> what they want, USB charger just tells the power driver how much
>> current need to draw. But we can add some checking if the setting
>> current is in the right range.
>
> The USB configuration tells the Host how much power it needs.  If the
> host enables the configuration, that implicitly say that much power is
> available, so the power_driver can safely request it.  I'm mostly happy
> wit that aspect of your patch set.

OK.

>
> For a dedicated charger there is no USB configuration.  The electrical
> properties of the cable provide some information about how the charger
> will behave, but they only guarantee a minimum.  If you want to use more
> than the minimum, you have to do so carefully and watch the voltage level.
> You cannot sensible let the user tell you how much current the charger
> can provide, because they'll probably get it wrong and the charger will
> just shut down.

Current validation is need in USB charger to guarantee the current is
available. If user set one unavailable current, we can ignore it or
change to the minimum, right? Thanks.

>
> Thanks,
> NeilBrown
>
>
>>
>> Thanks for your comments.
>>
>>>
>>>
>>> A more details discussion of this problem-space can be found at
>>>    https://lwn.net/Articles/693027/
>>> and an analysis of the functionality currently available in the kernel
>>> (which adds a number of specifics to the above) can be found at
>>>    https://lwn.net/Articles/694062/
>>>
>>> NeilBrown
>>>
>>>
>>
>>
>>
>> --
>> Baolin.wang
>> Best Regards



-- 
Baolin.wang
Best Regards

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#1479576 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

[Multipart message — attachments visible in raw view] — view raw

On Thu, Sep 08 2016, Baolin Wang wrote:

> On 8 September 2016 at 15:31, NeilBrown <neilb@suse.com> wrote:
>> On Thu, Sep 08 2016, Baolin Wang wrote:
>>>
>>> Now the usb charger will not get charger type from 'extcon' subsystem,
>>> we get the charger type from 'power_supply' and calllback
>>> 'get_charger_type' for users.
>>
>> I understand this.  I think it is wrong because, in general, the
>> power_supply doesn't know what the charger_type is (it might know it is
>> USB, but most don't know which sort of USB).  The PHY knows that, not
>> the power_supply.
>
> I don't think so. Now many platforms will detect the charger type by
> PMIC hardware, and we can get the charger type by PMIC hardware
> register. Then power supply driver can access the PMIC register to get
> the charger type. Here USB charger just considers if the accessing the
> PMIC register to get charger type is implemented in power supply, it
> is optional depending on what your platform designed.
>

In practice, the USB PHY and the Power manager will often be in the same
IC (the PMIC) so the driver for one could look at the registers for the
other.
But there is no guarantee that the hardware works like that.  It is
best to create a generally design.
Conceptually, the PHY is separate from the power manager and a solution
which recognises that will be more universal.

If the power manager can always just look at that phy registers to know
what sort of charger is connected, why does you framework need to work
with charger types at all?

>>>
>>> Yes, but you must think about some special cases on some platforms.
>>> Users may need to change the current in some situations, thus we
>>> should export one API for users to change the current. (I think you
>>> misunderstand the current limit here, that is the current for power
>>> driver  to draw).
>>
>> Can you be specific about these "special cases" please?
>> I cannot think of any.
>
> Suppose the USB configuration requests 100mA, then we should set the
> USB charger current is 100mA by __usb_charger_set_cur_limit_by_type()
> funtion, then notify this to power driver.

ahh.... I had missed something there.  It's a while since I looked
closely at these patches.

Only.... this usage of usb_charger_set_cur_limit_by_type() is really
nonsensical.

If the cable is detected as being DCP or CDP or ACA (or ACA/DOCK) then
the number negotiated with the USB configuration is not relevant and
should be ignored.  There is a guaranteed minimum which is at least the
maximum that *can* be negotiated.

It is only when the cable appears to be a SDP (standard downstream
port) that the usb-config negotiation is relevant.  That is because the
minimum guaranteed for SDP is only 100mA.

NeilBrown

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#1479692

On 9 September 2016 at 07:13, NeilBrown <neilb@suse.com> wrote:
> On Thu, Sep 08 2016, Baolin Wang wrote:
>
>> On 8 September 2016 at 15:31, NeilBrown <neilb@suse.com> wrote:
>>> On Thu, Sep 08 2016, Baolin Wang wrote:
>>>>
>>>> Now the usb charger will not get charger type from 'extcon' subsystem,
>>>> we get the charger type from 'power_supply' and calllback
>>>> 'get_charger_type' for users.
>>>
>>> I understand this.  I think it is wrong because, in general, the
>>> power_supply doesn't know what the charger_type is (it might know it is
>>> USB, but most don't know which sort of USB).  The PHY knows that, not
>>> the power_supply.
>>
>> I don't think so. Now many platforms will detect the charger type by
>> PMIC hardware, and we can get the charger type by PMIC hardware
>> register. Then power supply driver can access the PMIC register to get
>> the charger type. Here USB charger just considers if the accessing the
>> PMIC register to get charger type is implemented in power supply, it
>> is optional depending on what your platform designed.
>>
>
> In practice, the USB PHY and the Power manager will often be in the same
> IC (the PMIC) so the driver for one could look at the registers for the
> other.
> But there is no guarantee that the hardware works like that.  It is
> best to create a generally design.

Yes, we hope to create one generally design, so we need to consider
this situation: the power supply getting the charger type by accessing
PMIC registers. The registers which save the charger type are not
always belong to the USB PHY, may be just some registers on PMIC.

Now in mainline kernel, there are 3 methods can get the charger type
which need to integrate with USB charger framework:
1. power supply
2. extcon (need to add as you suggested)
3. others (by 'get_charger_type' callback of USB charger)

> Conceptually, the PHY is separate from the power manager and a solution
> which recognises that will be more universal.
>
> If the power manager can always just look at that phy registers to know
> what sort of charger is connected, why does you framework need to work
> with charger types at all?
>
>>>>
>>>> Yes, but you must think about some special cases on some platforms.
>>>> Users may need to change the current in some situations, thus we
>>>> should export one API for users to change the current. (I think you
>>>> misunderstand the current limit here, that is the current for power
>>>> driver  to draw).
>>>
>>> Can you be specific about these "special cases" please?
>>> I cannot think of any.
>>
>> Suppose the USB configuration requests 100mA, then we should set the
>> USB charger current is 100mA by __usb_charger_set_cur_limit_by_type()
>> funtion, then notify this to power driver.
>
> ahh.... I had missed something there.  It's a while since I looked
> closely at these patches.
>
> Only.... this usage of usb_charger_set_cur_limit_by_type() is really
> nonsensical.
>
> If the cable is detected as being DCP or CDP or ACA (or ACA/DOCK) then
> the number negotiated with the USB configuration is not relevant and
> should be ignored.  There is a guaranteed minimum which is at least the
> maximum that *can* be negotiated.

Yes. If it is not relevant, we will no't set the current from USB
configuration. Just when your charger type is SDP and the USB
enumeration is done, we can get the USB configuration from host to set
current.

>
> It is only when the cable appears to be a SDP (standard downstream
> port) that the usb-config negotiation is relevant.  That is because the
> minimum guaranteed for SDP is only 100mA.
>
> NeilBrown



-- 
Baolin.wang
Best Regards

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#1480360 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Fri, Sep 09 2016, Baolin Wang wrote:

>>
>> In practice, the USB PHY and the Power manager will often be in the same
>> IC (the PMIC) so the driver for one could look at the registers for the
>> other.
>> But there is no guarantee that the hardware works like that.  It is
>> best to create a generally design.
>
> Yes, we hope to create one generally design, so we need to consider
> this situation: the power supply getting the charger type by accessing
> PMIC registers. The registers which save the charger type are not
> always belong to the USB PHY, may be just some registers on PMIC.

If the power_supply can directly detect the type of charger, then it
doesn't need any usb-charger-infrastructure to tell it.  It can handle
current selection entirely internally.
Surely the only interesting case for a framework to address is the one
where the power_supply cannot directly detect the charger type.

>
> Now in mainline kernel, there are 3 methods can get the charger type
> which need to integrate with USB charger framework:
> 1. power supply
> 2. extcon (need to add as you suggested)
> 3. others (by 'get_charger_type' callback of USB charger)

There is no "get_charger_type" now in the mainline kernel.

>>>
>>> Suppose the USB configuration requests 100mA, then we should set the
>>> USB charger current is 100mA by __usb_charger_set_cur_limit_by_type()
>>> funtion, then notify this to power driver.
>>
>> ahh.... I had missed something there.  It's a while since I looked
>> closely at these patches.
>>
>> Only.... this usage of usb_charger_set_cur_limit_by_type() is really
>> nonsensical.
>>
>> If the cable is detected as being DCP or CDP or ACA (or ACA/DOCK) then
>> the number negotiated with the USB configuration is not relevant and
>> should be ignored.  There is a guaranteed minimum which is at least the
>> maximum that *can* be negotiated.
>
> Yes. If it is not relevant, we will no't set the current from USB
> configuration. Just when your charger type is SDP and the USB
> enumeration is done, we can get the USB configuration from host to set
> current.

But you do!
The mA number from the USB configuration is passed to usb_gadget_vbus_draw.
Your patch passes that to usb_charger_set_cur_limit_by_type()
which calls __usb_charger_set_cur_limit_by_type() which will set the
cur_limit for whichever type uchger->type currently is.

So when it is not relevant, your code *does* set some current limit.

NeilBrown

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#1485751

Hi Neil,

Sorry for late reply due yo my holiday.

On 10 September 2016 at 05:19, NeilBrown <neilb@suse.com> wrote:
> On Fri, Sep 09 2016, Baolin Wang wrote:
>
>>>
>>> In practice, the USB PHY and the Power manager will often be in the same
>>> IC (the PMIC) so the driver for one could look at the registers for the
>>> other.
>>> But there is no guarantee that the hardware works like that.  It is
>>> best to create a generally design.
>>
>> Yes, we hope to create one generally design, so we need to consider
>> this situation: the power supply getting the charger type by accessing
>> PMIC registers. The registers which save the charger type are not
>> always belong to the USB PHY, may be just some registers on PMIC.
>
> If the power_supply can directly detect the type of charger, then it
> doesn't need any usb-charger-infrastructure to tell it.  It can handle
> current selection entirely internally.
> Surely the only interesting case for a framework to address is the one
> where the power_supply cannot directly detect the charger type.

But power supply also need one plugged or unplugged event to set
current from USB charger framework. Another hand, considering one
generic framework, since power supply support API (e.g.:
power_supply_get_property()) to get charger type for others, we should
integrate power supply into USB charger framework.

>
>>
>> Now in mainline kernel, there are 3 methods can get the charger type
>> which need to integrate with USB charger framework:
>> 1. power supply
>> 2. extcon (need to add as you suggested)
>> 3. others (by 'get_charger_type' callback of USB charger)
>
> There is no "get_charger_type" now in the mainline kernel.

We want to create one generic framework, thus we should consider some
users want to implement the function to get charger type by accessing
PMIC registers or else.

>
>>>>
>>>> Suppose the USB configuration requests 100mA, then we should set the
>>>> USB charger current is 100mA by __usb_charger_set_cur_limit_by_type()
>>>> funtion, then notify this to power driver.
>>>
>>> ahh.... I had missed something there.  It's a while since I looked
>>> closely at these patches.
>>>
>>> Only.... this usage of usb_charger_set_cur_limit_by_type() is really
>>> nonsensical.
>>>
>>> If the cable is detected as being DCP or CDP or ACA (or ACA/DOCK) then
>>> the number negotiated with the USB configuration is not relevant and
>>> should be ignored.  There is a guaranteed minimum which is at least the
>>> maximum that *can* be negotiated.
>>
>> Yes. If it is not relevant, we will no't set the current from USB
>> configuration. Just when your charger type is SDP and the USB
>> enumeration is done, we can get the USB configuration from host to set
>> current.
>
> But you do!
> The mA number from the USB configuration is passed to usb_gadget_vbus_draw.
> Your patch passes that to usb_charger_set_cur_limit_by_type()
> which calls __usb_charger_set_cur_limit_by_type() which will set the
> cur_limit for whichever type uchger->type currently is.
>
> So when it is not relevant, your code *does* set some current limit.

Suppose the charger type is DCP(it is not relevant to the mA number
from the USB configuration ), it will not do the USB enumeration, then
no USB configuration from host to set current.

-- 
Baolin.wang
Best Regards

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#1479868

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On Fri, Sep 09, 2016 at 09:13:31AM +1000, NeilBrown wrote:

> Conceptually, the PHY is separate from the power manager and a solution
> which recognises that will be more universal.

The wm831x driver in the patch series is an example of such hardware -
it is purely a power manager, it has no USB PHY hardware at all.  It's a
current limiter intended to sit in line with the USB power lines to
ensure the system doesn't go over the maximum current draw (and also
integrates with the power source selection logic the chip has to pick
the best available power source for the system).

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#1480377 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Fri, Sep 09 2016, Mark Brown wrote:

> [ Unknown signature status ]
> On Fri, Sep 09, 2016 at 09:13:31AM +1000, NeilBrown wrote:
>
>> Conceptually, the PHY is separate from the power manager and a solution
>> which recognises that will be more universal.
>
> The wm831x driver in the patch series is an example of such hardware -
> it is purely a power manager, it has no USB PHY hardware at all.  It's a
> current limiter intended to sit in line with the USB power lines to
> ensure the system doesn't go over the maximum current draw (and also
> integrates with the power source selection logic the chip has to pick
> the best available power source for the system).

It might be instructive to look at exactly what happens with this
device.
The "probe" routine calls

 +			usb_charger_find_by_name(wm831x_pdata->usb_gadget);

Presumably wm831x_pdata is initialised by a board file?
I strongly suspect it is initialized to  "usb-charger.0" because the
names given to usb chargers are "usb-charger.%d" in discovery order.
I don't see this being at all useful if there is ever more than one
usb-charger.
Do you?

The probe function then registers for charger notifications.  When they
arrive, wm831x_usb_limit_change() will set the highest supported limit
which is less than the notified "limit".  So presumably that "limit"
must be the minimum guaranteed by the charger type.

Let's see when the notification is called...
->uchgr_nh is sent a notification from usb_charger_notify_others()
with (in the "charger is present" case) the value of
   __usb_charger_get_cur_limit(uchger)
which just pulls values out of the cur_limit structure, based on the
type, reported by
		usb_charger_get_type_by_others(uchger);
(The default values in this structure are not the minimums guaranteed
by the charger types, they are generally higher.  So this could easily
result in the charger shutting down).

usb_charger_get_type_by_others()  has two ways to get the charger
type, which it then caches in uchger->type until the charger is removed.

If there is a uchger->psy power supply, then the
  POWER_SUPPLY_PROP_CHARGE_TYPE
property is used...  Oh, that is weird.
The valid values for that property are:

enum {
        POWER_SUPPLY_CHARGE_TYPE_UNKNOWN = 0,
        POWER_SUPPLY_CHARGE_TYPE_NONE,
        POWER_SUPPLY_CHARGE_TYPE_TRICKLE,
        POWER_SUPPLY_CHARGE_TYPE_FAST,
};

but the code in usb_charger_get_type_by_others() compares it against:
 +		case POWER_SUPPLY_TYPE_USB:
 +		case POWER_SUPPLY_TYPE_USB_DCP:
 +		case POWER_SUPPLY_TYPE_USB_CDP:
 +		case POWER_SUPPLY_TYPE_USB_ACA:

Presumably that it just a bug and it was meant to request the
  POWER_SUPPLY_PROP_TYPE ??
I wonder how much testing was done on this code?

Anyway, assuming it is meant to request the TYPE, where is that set?
The new code doesn't set it at all.
Only three existing power supplies set any of
  POWER_SUPPLY_TYPE_USB_*
axp288_charger.c  gpio-charger.c isp1704_charger.c
As I wrote in https://lwn.net/Articles/694062/
axp288_charger.c is broken and cannot possibly work.
gpio-charger.c configures the type at boot-time so it cannot sensibly
detect a newly plugged in charger (how does that make any sense)
and isp1704_charger.c peeks in the usb registers (ULPI) to work out
the charger type.

None of these set the  POWER_SUPPLY_PROP_TYPE in a useful way, so why
would usb_charger_get_type_by_others() want to use that property?

Maybe it really does want to use POWER_SUPPLY_PROP_CHARGE_TYPE?
Quite a few chargers set that.  It would be a challenge to map names
like "TRICKLE" and "FAST" into mA values for a current limiter though.
My hardware knowledge is running out here.. I see wm8350_power.c reports
that property, but I don't know how that device fits into the picture.
With the patch, that driver would request that property from somewhere
else(?) and also report it.  That is kind-a strange.

The other possible source for the charger type is a call to
   uchger->get_charger_type()

There is no get_charger_type() function anywhere in the patchset.  No code
ever sets that field in the uchger.

So how can this wm831x driver actually find out what sort of charger is
connected and so set the power limit?  I just don't see this working *at*
*all*.

NeilBrown

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#1481208

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On Sat, Sep 10, 2016 at 07:57:26AM +1000, NeilBrown wrote:
> On Fri, Sep 09 2016, Mark Brown wrote:

> > The wm831x driver in the patch series is an example of such hardware -
> > it is purely a power manager, it has no USB PHY hardware at all.  It's a

> The "probe" routine calls

>  +			usb_charger_find_by_name(wm831x_pdata->usb_gadget);

> Presumably wm831x_pdata is initialised by a board file?

Yes.

> I strongly suspect it is initialized to  "usb-charger.0" because the
> names given to usb chargers are "usb-charger.%d" in discovery order.
> I don't see this being at all useful if there is ever more than one
> usb-charger.
> Do you?

It's no worse than any other board file situation - if someone has that
problem they get to fix it.

> So how can this wm831x driver actually find out what sort of charger is
> connected and so set the power limit?  I just don't see this working *at*
> *all*.

The whole point from the point of view of the wm831x driver is that it
just wants something to tell it how much current it's allowed to draw, I
appreciate that doesn't change your analysis of the bit in the middle
but the consumer driver bit seems fine here.

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#1481274 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Mon, Sep 12 2016, Mark Brown wrote:

> [ Unknown signature status ]
> On Sat, Sep 10, 2016 at 07:57:26AM +1000, NeilBrown wrote:
>> On Fri, Sep 09 2016, Mark Brown wrote:
>
>> > The wm831x driver in the patch series is an example of such hardware -
>> > it is purely a power manager, it has no USB PHY hardware at all.  It's a
>
>> The "probe" routine calls
>
>>  +			usb_charger_find_by_name(wm831x_pdata->usb_gadget);
>
>> Presumably wm831x_pdata is initialised by a board file?
>
> Yes.
>
>> I strongly suspect it is initialized to  "usb-charger.0" because the
>> names given to usb chargers are "usb-charger.%d" in discovery order.
>> I don't see this being at all useful if there is ever more than one
>> usb-charger.
>> Do you?
>
> It's no worse than any other board file situation - if someone has that
> problem they get to fix it.

My point is that the present design does not appear to scale beyond a
single USB power supply (as if there were two, they would be named in
discovery order, which is not reliably stable).

Your point is, I think, that when someone actually cares about that lack
of scaling, they can fix it.

I am perfectly happy with that approach.  However if the code doesn't
scale beyond one charger, it shouldn't pretend that it does.
i.e.
  Don't have "usb_charger_find_by_name()", just a global "usb_charger"
  (or similar).
  The first charger to register gets to be the "usb_charger".  The
  second one gets an error.
I could be quite happy with that sort of interface.

>
>> So how can this wm831x driver actually find out what sort of charger is
>> connected and so set the power limit?  I just don't see this working *at*
>> *all*.
>
> The whole point from the point of view of the wm831x driver is that it
> just wants something to tell it how much current it's allowed to draw, I
> appreciate that doesn't change your analysis of the bit in the middle
> but the consumer driver bit seems fine here.

Yes, the wm831x driver probably does the right thing.
Other drivers might want to know not only the minimum they are allowed
to draw, but also the maximum they should try even if they are carefully
monitoring the voltage.
So wm831x is doing the right thing with the wrong interface.  Maybe you
can describe that as "fine".

NeilBrown

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#1481424

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On Mon, Sep 12, 2016 at 03:27:18PM +0200, NeilBrown wrote:
> On Mon, Sep 12 2016, Mark Brown wrote:

> > It's no worse than any other board file situation - if someone has that
> > problem they get to fix it.

> My point is that the present design does not appear to scale beyond a
> single USB power supply (as if there were two, they would be named in
> discovery order, which is not reliably stable).

For the practical purposes of people making systems (as opposed to
upstream where this is likely to get most use) it pretty much is.
Though quite how many systems have multiple chargers is itself also a
question.

> Your point is, I think, that when someone actually cares about that lack
> of scaling, they can fix it.

Yes.

> I am perfectly happy with that approach.  However if the code doesn't
> scale beyond one charger, it shouldn't pretend that it does.
> i.e.
>   Don't have "usb_charger_find_by_name()", just a global "usb_charger"
>   (or similar).
>   The first charger to register gets to be the "usb_charger".  The
>   second one gets an error.
> I could be quite happy with that sort of interface.

Well, a fairly standard way of extending would be to allow the explicit
assignment of names to chargers so this'd avoid such churn.

> > The whole point from the point of view of the wm831x driver is that it
> > just wants something to tell it how much current it's allowed to draw, I
> > appreciate that doesn't change your analysis of the bit in the middle
> > but the consumer driver bit seems fine here.

> Yes, the wm831x driver probably does the right thing.
> Other drivers might want to know not only the minimum they are allowed
> to draw, but also the maximum they should try even if they are carefully
> monitoring the voltage.
> So wm831x is doing the right thing with the wrong interface.  Maybe you
> can describe that as "fine".

That's not actually 100% clear to me - for what the wm831x is doing it
probably *does* want the higher limit.  This is a system inflow limit
(as it should be for this), at least the charger will adapt to voltage
variations though other users in the system are much less likely to do
so.

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#1482227 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Mon, Sep 12 2016, Mark Brown wrote:

> [ Unknown signature status ]
> On Mon, Sep 12, 2016 at 03:27:18PM +0200, NeilBrown wrote:
>> On Mon, Sep 12 2016, Mark Brown wrote:
>
>> > It's no worse than any other board file situation - if someone has that
>> > problem they get to fix it.
>
>> My point is that the present design does not appear to scale beyond a
>> single USB power supply (as if there were two, they would be named in
>> discovery order, which is not reliably stable).
>
> For the practical purposes of people making systems (as opposed to
> upstream where this is likely to get most use) it pretty much is.
> Though quite how many systems have multiple chargers is itself also a
> question.
>
>> Your point is, I think, that when someone actually cares about that lack
>> of scaling, they can fix it.
>
> Yes.
>
>> I am perfectly happy with that approach.  However if the code doesn't
>> scale beyond one charger, it shouldn't pretend that it does.
>> i.e.
>>   Don't have "usb_charger_find_by_name()", just a global "usb_charger"
>>   (or similar).
>>   The first charger to register gets to be the "usb_charger".  The
>>   second one gets an error.
>> I could be quite happy with that sort of interface.
>
> Well, a fairly standard way of extending would be to allow the explicit
> assignment of names to chargers so this'd avoid such churn.

Sure, that might work.  I'm just against a design that obviously cannot
work.


>
>> > The whole point from the point of view of the wm831x driver is that it
>> > just wants something to tell it how much current it's allowed to draw, I
>> > appreciate that doesn't change your analysis of the bit in the middle
>> > but the consumer driver bit seems fine here.
>
>> Yes, the wm831x driver probably does the right thing.
>> Other drivers might want to know not only the minimum they are allowed
>> to draw, but also the maximum they should try even if they are carefully
>> monitoring the voltage.
>> So wm831x is doing the right thing with the wrong interface.  Maybe you
>> can describe that as "fine".
>
> That's not actually 100% clear to me - for what the wm831x is doing it
> probably *does* want the higher limit.  This is a system inflow limit
> (as it should be for this), at least the charger will adapt to voltage
> variations though other users in the system are much less likely to do
> so.

Interesting ... I hadn't considered that possibility.

As long as the current remains below the maximum, the charger will
reduce the voltage towards 2V as load increases.  Somewhere before it
gets there, the system will not be able to make use of the power as the
voltage will be too low to be usable. So that will naturally limit the
current being drawn.

Not having very much electrical engineering background, I cannot say for
sure what will happen, but it seems likely that once the voltage drops
much below 4.75V, the charger won't be operating at peak efficiency,
which would be a waste.
I can easily imagine that the hardware would switch off at some voltage
level, rather than just making do with what is there.
So I'm skeptical of this approach, but I'm open to being corrected by
someone more knowledgeable than I.

Looking at it from a different perspective, according to the patch set,
the limits that wm831x is able to impose are:

 +	0,
 +	2,
 +	100,
 +	500,
 +	900,
 +	1500,
 +	1800,
 +	550,

These are, from the battery charger spec, minimums rather than maximums.
e.g. a CDP provides at least 1500, and as much as 5000.  So it seems
that the wm831x was designed to be told the minimum guaranteed available.
But that is circumstantial evidence and might be misleading.

NeilBrown

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#1483191

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On Tue, Sep 13, 2016 at 10:00:28AM +0200, NeilBrown wrote:
> On Mon, Sep 12 2016, Mark Brown wrote:

> > That's not actually 100% clear to me - for what the wm831x is doing it
> > probably *does* want the higher limit.  This is a system inflow limit
> > (as it should be for this), at least the charger will adapt to voltage
> > variations though other users in the system are much less likely to do
> > so.

> Not having very much electrical engineering background, I cannot say for
> sure what will happen, but it seems likely that once the voltage drops
> much below 4.75V, the charger won't be operating at peak efficiency,
> which would be a waste.
> I can easily imagine that the hardware would switch off at some voltage
> level, rather than just making do with what is there.
> So I'm skeptical of this approach, but I'm open to being corrected by
> someone more knowledgeable than I.

Yes, the idea is that the charger will back off charging and stop
entirely if the rest of the system is consuming too much power to allow
it to continue effectively.  The same thing happens with wall power, if
a wall supply isn't able to power the charger (eg, because the rest of
the system is running flat out) it'll have to cope with that.

> Looking at it from a different perspective, according to the patch set,
> the limits that wm831x is able to impose are:

>  +	0,
>  +	2,
>  +	100,
>  +	500,
>  +	900,
>  +	1500,
>  +	1800,
>  +	550,

> These are, from the battery charger spec, minimums rather than maximums.
> e.g. a CDP provides at least 1500, and as much as 5000.  So it seems
> that the wm831x was designed to be told the minimum guaranteed available.
> But that is circumstantial evidence and might be misleading.

AIUI this is conservatisim in the system design - another way of reading
a spec with a range like this is that the consumer should aim for the
lower limit, the provider should aim for the upper limit and that way if
either of them has issues with tolerances things will still work out.
It predates wide availability of CDP so I wouldn't be surprised if that
bit were just an oversight.  Like I say this bit of hardware is totally
separate to the battery charger.

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#1483350 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Wed, Sep 14 2016, Mark Brown wrote:

> [ Unknown signature status ]
> On Tue, Sep 13, 2016 at 10:00:28AM +0200, NeilBrown wrote:
>> On Mon, Sep 12 2016, Mark Brown wrote:
>
>> > That's not actually 100% clear to me - for what the wm831x is doing it
>> > probably *does* want the higher limit.  This is a system inflow limit
>> > (as it should be for this), at least the charger will adapt to voltage
>> > variations though other users in the system are much less likely to do
>> > so.
>
>> Not having very much electrical engineering background, I cannot say for
>> sure what will happen, but it seems likely that once the voltage drops
>> much below 4.75V, the charger won't be operating at peak efficiency,
>> which would be a waste.
>> I can easily imagine that the hardware would switch off at some voltage
>> level, rather than just making do with what is there.
>> So I'm skeptical of this approach, but I'm open to being corrected by
>> someone more knowledgeable than I.
>
> Yes, the idea is that the charger will back off charging and stop
> entirely if the rest of the system is consuming too much power to allow
> it to continue effectively.  The same thing happens with wall power, if
> a wall supply isn't able to power the charger (eg, because the rest of
> the system is running flat out) it'll have to cope with that.

Maybe you are correct.  I don't find your argument convincing, but maybe
that is because I don't want to...
Some facts though:
 1/ I had a report once from someone whose device stopped charging
   because it was pulling more current than the charger could supply.
   The voltage dropped below the 3.5V (I think) that the battery
   charging hardware needed, so it switched off.  It wouldn't switch
   back on again until explicitly told too.  It would then overload the
   charger again and switch off.
   Changing the code to put a lower limit on the current allowed the
   battery to be charged.  So empirical evidence suggests that the
   lower number should be used.

 2/ I hoped that
      Battery Charging Specification
      Revision 1.2
      December 7, 2010

    would say something definite, but I cannot find it.
    However,  "note 1" to "Table 5-2 Currents" says:
     
        1) The maximum current is for safety reasons, as per USB 2.0 section 7.2.1.2.1.
     
    Which seems to say the maximum is just for safety, implying that the
    minimum is the important value.

 3/  Felipe Balbi <balbi@kernel.org>  appears to agree with my
   perspective.
      http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1224904.html
   does argument-by-authority work?


>
>> Looking at it from a different perspective, according to the patch set,
>> the limits that wm831x is able to impose are:
>
>>  +	0,
>>  +	2,
>>  +	100,
>>  +	500,
>>  +	900,
>>  +	1500,
>>  +	1800,
>>  +	550,
>
>> These are, from the battery charger spec, minimums rather than maximums.
>> e.g. a CDP provides at least 1500, and as much as 5000.  So it seems
>> that the wm831x was designed to be told the minimum guaranteed available.
>> But that is circumstantial evidence and might be misleading.
>
> AIUI this is conservatisim in the system design - another way of reading
> a spec with a range like this is that the consumer should aim for the
> lower limit, the provider should aim for the upper limit and that way if
> either of them has issues with tolerances things will still work out.
> It predates wide availability of CDP so I wouldn't be surprised if that
> bit were just an oversight.  Like I say this bit of hardware is totally
> separate to the battery charger.

Your last sentence is interesting .... I would reply "of course".
All the code we are talking about is only tangentially related to battery
charging.  It is about how much current can safely be pulled from a USB
port.  What that current is used for is a completely separate question.

NeilBrown

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#1483415

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On Wed, Sep 14, 2016 at 04:11:58PM +0200, NeilBrown wrote:
> On Wed, Sep 14 2016, Mark Brown wrote:

> > Yes, the idea is that the charger will back off charging and stop
> > entirely if the rest of the system is consuming too much power to allow
> > it to continue effectively.  The same thing happens with wall power, if
> > a wall supply isn't able to power the charger (eg, because the rest of
> > the system is running flat out) it'll have to cope with that.

> Maybe you are correct.  I don't find your argument convincing, but maybe
> that is because I don't want to...

There's a *huge* variation in how chargers are designed, some are
designed to be dumb and won't function without software while the wm831x
is more at the opposite end of the spectrum and will quite happily run
all the charging and power source selection logic with no software
intervention at all - the parameters it uses can be changed at runtime
but that's about it.  Software implementations are obviously more
flexible but hardware implementations can be more responsive to changes
in system state like drooping supplies and aren't vulnerable to things
like software lockups.

>  1/ I had a report once from someone whose device stopped charging
>  because it was pulling more current than the charger could supply.
>  The voltage dropped below the 3.5V (I think) that the battery
>  charging hardware needed, so it switched off.  It wouldn't switch
>  back on again until explicitly told too.  It would then overload the
>  charger again and switch off.

That's just one charger's algorithm though, other options are available.

>     Which seems to say the maximum is just for safety, implying that the
>     minimum is the important value.

This is what I was saying about a sensible reading being for the supply
and consumer side to directly target the maximum and minimum limits
respectively (though for the battery charger spec it's a bit different
as the range is so wide).

>  3/  Felipe Balbi <balbi@kernel.org>  appears to agree with my
>    perspective.
>       http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1224904.html
>    does argument-by-authority work?

TI do a lot of the more software managed chargers (which I suspect are
the main thing Felipe will have looked at) if that's what you're
referring to here?  The device is implementing pretty much the algorithm
you're describing in that e-mail so I'm a bit confused as to what you're
saying here.

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#1483513 — Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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On Wed, Sep 14 2016, Mark Brown wrote:

> TI do a lot of the more software managed chargers (which I suspect are
> the main thing Felipe will have looked at) if that's what you're
> referring to here?  The device is implementing pretty much the algorithm
> you're describing in that e-mail so I'm a bit confused as to what you're
> saying here.

Ah.... my mistake, sorry.
When earlier you said:
>                                                                 It's a
> current limiter intended to sit in line with the USB power lines to
> ensure the system doesn't go over the maximum current draw (and also
> integrates with the power source selection logic the chip has to pick
> the best available power source for the system).

I assumed that all it did was limit the current to number given.
If it also limits the current to ensure that voltage doesn't drop
unduly, then I agree with your assertion that it just needs to be told
the upper limit.
I hope you'll agree that other drivers might need to know the lower
limit, so reporting both to all drivers is sensible.

Thanks,
NeilBrown

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