linux-kernel - Re: [PATCH RFT 2/6] gpio: mmio: get chip label and GPIO base from device properties

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Message-ID: <CAMRc=MdEZkjoDR83JFg5OPP07_DkAfeZixN9C+uxhkqkxaKypg@mail.gmail.com>
Date: Wed, 25 Jun 2025 12:23:19 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Lee Jones <lee@...nel.org>, 
	Liviu Dudau <liviu.dudau@....com>, Sudeep Holla <sudeep.holla@....com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Aaro Koskinen <aaro.koskinen@....fi>, 
	Janusz Krzysztofik <jmkrzyszt@...il.com>, Tony Lindgren <tony@...mide.com>, 
	Russell King <linux@...linux.org.uk>, Alim Akhtar <alim.akhtar@...sung.com>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org, 
	patches@...nsource.cirrus.com, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH RFT 2/6] gpio: mmio: get chip label and GPIO base from
 device properties

On Wed, Jun 25, 2025 at 10:54 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 25/06/2025 09:35, Bartosz Golaszewski wrote:
> > On Tue, 24 Jun 2025 at 21:44, Linus Walleij <linus.walleij@...aro.org> wrote:
> >>
> >> On Tue, Jun 24, 2025 at 3:19 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >>
> >>> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >>>
> >>> Ahead of removing struct bgpio_pdata support from the gpio-mmio generic
> >>> module, let's add support for getting the relevant values from generic
> >>> device properties. "label" is a semi-standardized property in some GPIO
> >>> drivers so let's go with it. There's no standard "base" property, so
> >>> let's use the name "gpio-mmio,base" to tie it to this driver
> >>> specifically. The number of GPIOs will be retrieved using
> >>> gpiochip_get_ngpios() so there's no need to look it up in the software
> >>> node.
> >>>
> >>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >>
> >> This works for me.
> >> I wouldn't be stoked to see device trees abusing the "gpio-mmio,base"
> >> property all of a sudden just because it now exists as a device
> >> property though... I kind of wish we had a way to opt out of exposing
> >> this to all the sub-property paths. But it seems tiresome, so:
> >>
> >> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> >>
> >> Yours,
> >> Linus Walleij
> >
> > That's not a problem - this property is not in any DT bindings and as
> > such is not an allowed property in DT sources. For out-of-tree DTs? We
> > don't care about those.
> That's not true, we do care about implied ABI. Try changing/breaking
> this later, when users complain their out of tree DTS is affected, and
> explaining this all to Greg.
>

Wait, seriously? I thought that the upstream bindings are the source
of truth for device-tree sources...

> Rob was/is working on tools checking this for such implied ABI, I think.
> For of_xxx() calls it is obvious, for device_xxx() or fwnode_xxx() it is
> not, therefore please add a comment that this is not allowed to be used
> by Devicetree platforms (or that this is only for
> ACPI/platform_data/whatever). I don't have any other guideline/solution
> other than a comment.
>

Ok.

Bart