Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1291230 > unrolled thread

Re: [PATCH 1/3] Device tree binding documentation for gpio-switch

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [PATCH 1/3] Device tree binding documentation for gpio-switch Linus Walleij <linus.walleij@linaro.org> - 2015-12-14 15:30 +0100
    Re: [PATCH 1/3] Device tree binding documentation for gpio-switch Rob Herring <robh+dt@kernel.org> - 2015-12-14 16:50 +0100
      Re: [PATCH 1/3] Device tree binding documentation for gpio-switch Markus Pargmann <mpa@pengutronix.de> - 2015-12-15 10:20 +0100

#1291230 — Re: [PATCH 1/3] Device tree binding documentation for gpio-switch

On Fri, Dec 11, 2015 at 3:06 PM, Rob Herring <robh+dt@kernel.org> wrote:
> On Fri, Dec 11, 2015 at 6:39 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
>> On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch
>> <martyn.welch@collabora.co.uk> wrote:
>>
>>> This patch adds documentation for the gpio-switch binding. This binding
>>> provides a mechanism to bind named links to gpio, with the primary
>>> purpose of enabling standardised access to switches that might be standard
>>> across a group of devices but implemented differently on each device.
>>>
>>> Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
>>
>> As mentioned in the comment to the second patch, this solves the
>> following generic problem:
>>
>> Expose a GPIO line to userspace using a specific name
>>
>> That means basically naming GPIO lines and marking them as
>> "not used by the operating system".
>>
>> This is something that has been proposed before, and postponed
>> because the kernel lacks the right infrastructure.
>
> That doesn't necessarily mean we can't define a binding.

Yeah that's true. just saying that the other stuff was not merged
for this reason, but then we can have a look at Markus' bindings
in parallell, Markus can you repost them to this audience? Only
the bindings I mean.

>> Markus Pargmann also did a series that add initial values to
>> hogs, which is the inverse usecase of this, where you want to
>> *output* something by default, then maybe also make it available
>> to userspace.
>>
>> So what we need to see here is a patch series that does all of these
>> things:
>>
>> - Name lines
>>
>> - Sets them to initial values
>>
>> - Mark them as read-only
>>
>> - Mark them as "not used by the operating system" so that they
>>   can be default-exported to userspace.
>
> No! This should not be a DT property.
>
> Whether I want to control a GPIO in the kernel or userspace is not
> known and can change over time. It could simply depend on kernel
> config. There is also the case that a GPIO has no connection or kernel
> driver until some time later when a DT overlay for an expansion board
> is applied.

That's correct. So from a DT point of view, what really matters is
to give things a name, and the hogs and initvals syntax already
has a structure for this that is in use
(from Documentation/devicetree/bindings/gpio/gpio.txt):

        qe_pio_a: gpio-controller@1400 {
                compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
                reg = <0x1400 0x18>;
                gpio-controller;
                #gpio-cells = <2>;

                line_b {
                        gpio-hog;
                        gpios = <6 0>;
                        output-low;
                        line-name = "foo-bar-gpio";
                };
        };

Markus use this also for initial values. That could easily be used in
a budget version like this:

                line_b {
                        /* Just naming */
                        gpios = <6 0>;
                        line-name = "foo-bar-gpio";
                };

That could grow kind of big though. Or maybe not? How many
GPIO lines are actually properly named in a typical system?

The problem is that naming is usually imposed by consumers (they
are the ones who know how the line is used).

And then I do not mean naming it after the pin on the capsule
where it comes out as per the datasheet, but
naming it after the actual use.

Naming it after the hardware specs is something the operating
system can do, in Linux' case by the array char *names; inside the
struct gpio_chip and should not be part of the bindings IMO.

I would rather imagine this is something used in a top-level board
file naming it: "header-2-22" for the 22nd pin on some second header
on my BeagleBone Black or something like that. And those may not
be so vast in numbers so they could be named using this pattern.

Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1291304

On Mon, Dec 14, 2015 at 8:28 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Fri, Dec 11, 2015 at 3:06 PM, Rob Herring <robh+dt@kernel.org> wrote:
>> On Fri, Dec 11, 2015 at 6:39 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
>>> On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch
>>> <martyn.welch@collabora.co.uk> wrote:

[...]

>>> Markus Pargmann also did a series that add initial values to
>>> hogs, which is the inverse usecase of this, where you want to
>>> *output* something by default, then maybe also make it available
>>> to userspace.
>>>
>>> So what we need to see here is a patch series that does all of these
>>> things:
>>>
>>> - Name lines
>>>
>>> - Sets them to initial values
>>>
>>> - Mark them as read-only
>>>
>>> - Mark them as "not used by the operating system" so that they
>>>   can be default-exported to userspace.
>>
>> No! This should not be a DT property.
>>
>> Whether I want to control a GPIO in the kernel or userspace is not
>> known and can change over time. It could simply depend on kernel
>> config. There is also the case that a GPIO has no connection or kernel
>> driver until some time later when a DT overlay for an expansion board
>> is applied.
>
> That's correct. So from a DT point of view, what really matters is
> to give things a name, and the hogs and initvals syntax already
> has a structure for this that is in use
> (from Documentation/devicetree/bindings/gpio/gpio.txt):
>
>         qe_pio_a: gpio-controller@1400 {
>                 compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
>                 reg = <0x1400 0x18>;
>                 gpio-controller;
>                 #gpio-cells = <2>;
>
>                 line_b {
>                         gpio-hog;
>                         gpios = <6 0>;
>                         output-low;
>                         line-name = "foo-bar-gpio";
>                 };
>         };
>
> Markus use this also for initial values. That could easily be used in
> a budget version like this:
>
>                 line_b {
>                         /* Just naming */
>                         gpios = <6 0>;
>                         line-name = "foo-bar-gpio";
>                 };
>
> That could grow kind of big though. Or maybe not? How many
> GPIO lines are actually properly named in a typical system?

We should limit it to GPIOs with no connection to another node. For
example, I don't want to see a SD card detect in the list as that
should be in the SD host node. However, that is hard to enforce and
can change over time. Removing it would break userspace potentially.
Of course if the kernel starts own a signal that userspace used, then
that potentially breaks userspace regardless of the DT changing. OTOH,
using GPIOs in userspace is kind of use at your own risk.

The only real differences between this and Martyn's proposal are the
location of the nodes and having a compatible string. A compatible
string may be good to have. It indicates type of signal, but not
specific use. Similar to how gpio-key compatible defines the function,
but not what key code, or gpio-led does not say what color LED. A
compatible here could cover switches, mode/id/revision strapping
signals, jumpers, presence detect, etc.

> The problem is that naming is usually imposed by consumers (they
> are the ones who know how the line is used).
>
> And then I do not mean naming it after the pin on the capsule
> where it comes out as per the datasheet, but
> naming it after the actual use.

Right. We need a way to query "I need the GPIO that does X" which
works across boards.

> Naming it after the hardware specs is something the operating
> system can do, in Linux' case by the array char *names; inside the
> struct gpio_chip and should not be part of the bindings IMO.

Agreed. That just came up with STM32 gpio bindings[1].

> I would rather imagine this is something used in a top-level board
> file naming it: "header-2-22" for the 22nd pin on some second header
> on my BeagleBone Black or something like that. And those may not
> be so vast in numbers so they could be named using this pattern.

Exactly. This is one of the cases I care about. However, this is not
really a function, but it is SOC independent at least.

We also have to consider how to handle add-on boards. We probably need
a connector node which can remap connector signals to host signals in
order to have overlays independent of the host board DT. For GPIOs
this is probably a gpio-map property similar to interrupt-map. The
complicated part will be connectors that require pinmux setup of the
host.

Rob

[1] https://lkml.org/lkml/2015/12/11/600
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1291958

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

Hi,

On Monday 14 December 2015 09:45:48 Rob Herring wrote:
> On Mon, Dec 14, 2015 at 8:28 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Fri, Dec 11, 2015 at 3:06 PM, Rob Herring <robh+dt@kernel.org> wrote:
> >> On Fri, Dec 11, 2015 at 6:39 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> >>> On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch
> >>> <martyn.welch@collabora.co.uk> wrote:
> 
> [...]
> 
> >>> Markus Pargmann also did a series that add initial values to
> >>> hogs, which is the inverse usecase of this, where you want to
> >>> *output* something by default, then maybe also make it available
> >>> to userspace.
> >>>
> >>> So what we need to see here is a patch series that does all of these
> >>> things:
> >>>
> >>> - Name lines
> >>>
> >>> - Sets them to initial values
> >>>
> >>> - Mark them as read-only
> >>>
> >>> - Mark them as "not used by the operating system" so that they
> >>>   can be default-exported to userspace.
> >>
> >> No! This should not be a DT property.
> >>
> >> Whether I want to control a GPIO in the kernel or userspace is not
> >> known and can change over time. It could simply depend on kernel
> >> config. There is also the case that a GPIO has no connection or kernel
> >> driver until some time later when a DT overlay for an expansion board
> >> is applied.
> >
> > That's correct. So from a DT point of view, what really matters is
> > to give things a name, and the hogs and initvals syntax already
> > has a structure for this that is in use
> > (from Documentation/devicetree/bindings/gpio/gpio.txt):
> >
> >         qe_pio_a: gpio-controller@1400 {
> >                 compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
> >                 reg = <0x1400 0x18>;
> >                 gpio-controller;
> >                 #gpio-cells = <2>;
> >
> >                 line_b {
> >                         gpio-hog;
> >                         gpios = <6 0>;
> >                         output-low;
> >                         line-name = "foo-bar-gpio";
> >                 };
> >         };
> >
> > Markus use this also for initial values. That could easily be used in
> > a budget version like this:
> >
> >                 line_b {
> >                         /* Just naming */
> >                         gpios = <6 0>;
> >                         line-name = "foo-bar-gpio";
> >                 };
> >
> > That could grow kind of big though. Or maybe not? How many
> > GPIO lines are actually properly named in a typical system?
> 
> We should limit it to GPIOs with no connection to another node. For
> example, I don't want to see a SD card detect in the list as that
> should be in the SD host node. However, that is hard to enforce and
> can change over time. Removing it would break userspace potentially.
> Of course if the kernel starts own a signal that userspace used, then
> that potentially breaks userspace regardless of the DT changing. OTOH,
> using GPIOs in userspace is kind of use at your own risk.

I see this a bit differently. I would really like to see the each GPIO having
two different names:
- GPIO label: This is the name of the GPIO line in the schematic for example
- GPIO use (this is the current semantic of the GPIO name): The use of a GPIO,
  e.g. 'sd-card-detect', 'LED', ...

I think it would be good to describe all GPIO labels in gpiochip subnodes as
gpio-hogging introduced it. This would offer a use-independent naming. The use
of the function could be defined in the device node that is using this gpio.

As an example perhaps something like this:

	&gpiochip {
		some_interrupt {
			gpios = <4 0>;
			line-name = "some_interrupt_line";
		};

		line_b {
			gpios = <6 0>;
			line-name = "line-b";
		};
	};

	randomswitch {
		compatible = "gpio-switch";
		gpios = <&gpiochip 4 0>;
		use = "action-trigger";
		read-only;
	};

Also this does seem kind of inconsistent with gpio-hogging and the proposed
gpio-initval. gpio-hogging is defined in subnodes of the gpio chip while
gpio-switches are not. As "gpio-switch" is not really any kind of device it
would perhaps make sense to keep this consistent with gpio-hogging as well and
define it in the same subnodes?
I would be happy about any consistent way.

> 
> The only real differences between this and Martyn's proposal are the
> location of the nodes and having a compatible string. A compatible
> string may be good to have. It indicates type of signal, but not
> specific use. Similar to how gpio-key compatible defines the function,
> but not what key code, or gpio-led does not say what color LED. A
> compatible here could cover switches, mode/id/revision strapping
> signals, jumpers, presence detect, etc.
> 
> > The problem is that naming is usually imposed by consumers (they
> > are the ones who know how the line is used).
> >
> > And then I do not mean naming it after the pin on the capsule
> > where it comes out as per the datasheet, but
> > naming it after the actual use.
> 
> Right. We need a way to query "I need the GPIO that does X" which
> works across boards.
> 
> > Naming it after the hardware specs is something the operating
> > system can do, in Linux' case by the array char *names; inside the
> > struct gpio_chip and should not be part of the bindings IMO.
> 
> Agreed. That just came up with STM32 gpio bindings[1].
> 
> > I would rather imagine this is something used in a top-level board
> > file naming it: "header-2-22" for the 22nd pin on some second header
> > on my BeagleBone Black or something like that. And those may not
> > be so vast in numbers so they could be named using this pattern.
> 
> Exactly. This is one of the cases I care about. However, this is not
> really a function, but it is SOC independent at least.
> 
> We also have to consider how to handle add-on boards. We probably need
> a connector node which can remap connector signals to host signals in
> order to have overlays independent of the host board DT. For GPIOs
> this is probably a gpio-map property similar to interrupt-map. The
> complicated part will be connectors that require pinmux setup of the
> host.

Also what about hotplugging gpio-chips? Is there any mechanism to let the
'gpio-switch' know that the GPIO is not there anymore?

Best Regards,

Markus

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web