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

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Message-ID: <6c64751d-67f6-4c30-a312-af289d9f432e@kernel.org>
Date: Wed, 25 Jun 2025 10:53:53 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
 Linus Walleij <linus.walleij@...aro.org>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, 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 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.

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.

Best regards,
Krzysztof