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[PATCH RFC 0/2] simplefb: Add regulator handling support

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  [PATCH RFC 0/2] simplefb: Add regulator handling support Chen-Yu Tsai <wens@csie.org> - 2015-10-12 19:10 +0200
    Re: [PATCH RFC 0/2] simplefb: Add regulator handling support Hans de Goede <hdegoede@redhat.com> - 2015-10-13 09:20 +0200
      Re: [PATCH RFC 0/2] simplefb: Add regulator handling support Mark Brown <broonie@kernel.org> - 2015-10-14 13:00 +0200
        Re: [PATCH RFC 0/2] simplefb: Add regulator handling support Hans de Goede <hdegoede@redhat.com> - 2015-10-14 13:40 +0200

#1244934 — [PATCH RFC 0/2] simplefb: Add regulator handling support

Hi everyone,

This series adds regulator claiming and enabling support for simplefb.

Sometimes the simplefb display output path consits of external conversion
chips and/or LCD drivers and backlights. These devices normally have
GPIOs to turn them on and/or bring them out of reset, and regulators
supplying power to them.

While the kernel does not touch unclaimed GPIOs, the regulator core
happily disables unused regulators. Thus we need simplefb to claim
and enable the regulators used throughout the display pipeline.

Now the DT bindings don't support a list of regulators directly, so
I'm working around it by having a "num-supplies" property to specify
the number of supply properties to check, and name the actual supplies
as "vinN-supply".

Hans, Maxime, AXP223 support for the A23/A33 Q8 tablets will need this
to keep the LCD on. The Primo81 needs this as well.


Patch 1 adds the regulator properties to the DT binding.

Patch 2 adds code to the simplefb driver to claim and enable regulators.


Regards
ChenYu


Chen-Yu Tsai (2):
  dt-bindings: simplefb: Support a list of regulator supply properties
  simplefb: Claim and enable regulators

 .../bindings/video/simple-framebuffer.txt          |  14 ++-
 drivers/video/fbdev/simplefb.c                     | 102 ++++++++++++++++++++-
 2 files changed, 111 insertions(+), 5 deletions(-)

-- 
2.5.3

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#1245405

Hi,

On 12-10-15 19:04, Chen-Yu Tsai wrote:
> Hi everyone,
>
> This series adds regulator claiming and enabling support for simplefb.
>
> Sometimes the simplefb display output path consits of external conversion
> chips and/or LCD drivers and backlights. These devices normally have
> GPIOs to turn them on and/or bring them out of reset, and regulators
> supplying power to them.
>
> While the kernel does not touch unclaimed GPIOs, the regulator core
> happily disables unused regulators. Thus we need simplefb to claim
> and enable the regulators used throughout the display pipeline.

Ack for doing something like this (adding regulator support) to simplefb,
it makes sense to have this.

> Now the DT bindings don't support a list of regulators directly, so
> I'm working around it by having a "num-supplies" property to specify
> the number of supply properties to check, and name the actual supplies
> as "vinN-supply".

Hmm, I can see the need for a "supplies" property with a list of regulators
in other use-cases (e.g. the generic mmc-pwrseq driver) too. Now as discussed
we can simply do vin0-supply - vinN-supply properties and be done with it,
but maybe we need to actually add support for a generic "supplies" property ?

And if not then maybe we need a few generic helper devm helper function which
takes a node, figures out how much vinN-supply properties there are and returns
a dynamically allocated array containing references to all the regulators, or
a PTR_ERR in case of err, at which point the caller is expected to fail the
probe so that any successfully acquired regulators are released.

Mark, what are your thoughts on this ?

Regards,

Hans
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#1246514

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On Tue, Oct 13, 2015 at 09:16:56AM +0200, Hans de Goede wrote:
> On 12-10-15 19:04, Chen-Yu Tsai wrote:

> >Now the DT bindings don't support a list of regulators directly, so
> >I'm working around it by having a "num-supplies" property to specify
> >the number of supply properties to check, and name the actual supplies
> >as "vinN-supply".

> Hmm, I can see the need for a "supplies" property with a list of regulators
> in other use-cases (e.g. the generic mmc-pwrseq driver) too. Now as discussed
> we can simply do vin0-supply - vinN-supply properties and be done with it,
> but maybe we need to actually add support for a generic "supplies" property ?

I really don't like having unnamed supplies, or supplies with names that
don't correspond to the schematic names for the physical supplies.  It
makes it harder to go between the DT and the schematic and encourages
bad practice on specific chip bindings which should be done properly
since it's harder to tell if the binding is done correctly.

Adding something with the pattern of parallel arrays of phandles and
names properties that got introduced after the regulator bindings were
done also means we need to go and update every single binding using
regulators to document the new properties which is going to be tedious
and require constant policing for a while.  I'm also not a big fan of
the pattern from a legibility point of view but that's a separate thing.

> And if not then maybe we need a few generic helper devm helper function which
> takes a node, figures out how much vinN-supply properties there are and returns
> a dynamically allocated array containing references to all the regulators, or
> a PTR_ERR in case of err, at which point the caller is expected to fail the
> probe so that any successfully acquired regulators are released.

I can see it for this sort of simplefb thing but I'm not sure how we'd
discourage drivers for specific hardware from also using the same helper
which then makes it easy to get sloppy board DTs which I'd expect to
lead to hassle down the road as drivers try to use their supplies and
find that actual DTs have things that don't correspond to reality in
them.  The nice thing about having drivers name the supplies they're
expecting is that it makes describing the board as it really is much
more the path of least resistance.

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#1246566

Hi,

On 14-10-15 12:55, Mark Brown wrote:
> On Tue, Oct 13, 2015 at 09:16:56AM +0200, Hans de Goede wrote:
>> On 12-10-15 19:04, Chen-Yu Tsai wrote:
>
>>> Now the DT bindings don't support a list of regulators directly, so
>>> I'm working around it by having a "num-supplies" property to specify
>>> the number of supply properties to check, and name the actual supplies
>>> as "vinN-supply".
>
>> Hmm, I can see the need for a "supplies" property with a list of regulators
>> in other use-cases (e.g. the generic mmc-pwrseq driver) too. Now as discussed
>> we can simply do vin0-supply - vinN-supply properties and be done with it,
>> but maybe we need to actually add support for a generic "supplies" property ?
>
> I really don't like having unnamed supplies, or supplies with names that
> don't correspond to the schematic names for the physical supplies.  It
> makes it harder to go between the DT and the schematic and encourages
> bad practice on specific chip bindings which should be done properly
> since it's harder to tell if the binding is done correctly.

Ok.

> Adding something with the pattern of parallel arrays of phandles and
> names properties that got introduced after the regulator bindings were
> done also means we need to go and update every single binding using
> regulators to document the new properties which is going to be tedious
> and require constant policing for a while.  I'm also not a big fan of
> the pattern from a legibility point of view but that's a separate thing.

Oh no, I was not suggesting to have this replace how we currently do
things, I was merely suggesting allowing to have a supplies list property
for bindings where a list of (unnamed) supplies makes sense like simplefb.

I fully agree that we do not want to see matching a supplies-names prop,
if names are needed the old name-supply schema should be used just like
it is today.

>> And if not then maybe we need a few generic helper devm helper function which
>> takes a node, figures out how much vinN-supply properties there are and returns
>> a dynamically allocated array containing references to all the regulators, or
>> a PTR_ERR in case of err, at which point the caller is expected to fail the
>> probe so that any successfully acquired regulators are released.
>
> I can see it for this sort of simplefb thing but I'm not sure how we'd
> discourage drivers for specific hardware from also using the same helper
> which then makes it easy to get sloppy board DTs which I'd expect to
> lead to hassle down the road as drivers try to use their supplies and
> find that actual DTs have things that don't correspond to reality in
> them.  The nice thing about having drivers name the supplies they're
> expecting is that it makes describing the board as it really is much
> more the path of least resistance.

Ok, so as said I see some value in this for generic drivers like
simplefb, mmc-pwrseq, but also the generic ahci-platform, ohci-platform
and ehci-platform drivers, where often it is possible to use the generic
driver (together with a soc specific phy driver) without needing to
introduce new compatibles, as all we need is to specify a phy(s),
bunch of clocks, resets, etc. It would be good IMHO if we could specify
e.g. this is a generic ehci block, which needs this list of supplies
to be enabled (note typically the supplies are tied to the phy, so
maybe not the best example).

I like your idea in your other mail where you suggest to actually
use foo-supply and bar-supply names in the simplefb node, and then have
some code simple iterate over all the properties and check for *-supply
properties, so that the proper, schematic matching names can be used.

But surely if we go this way having a helper for this so that others
can re-use that likely not entirely trivial code is a good idea ?

One user which comes to mind immediately here is the generic mmc-pwrseq
driver.

I agree that we need to be careful to not use a helper like this too
much, but I do believe it will make sense to have it in some rare cases.
We can put a big warning in both the header declaring it and above
the implementation to use it scarcely.

Regards,

Hans
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