linux-kernel - Re: [PATCH 0/4] Fix Samsung pinctrl driver static allocation of GPIO base warning

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Message-ID: <82e30bd1-b7b4-4d95-9f13-008398082ca0@linaro.org>
Date:   Mon, 9 Oct 2023 11:42:07 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sam Protsenko <semen.protsenko@...aro.org>
Cc:     Mateusz Majewski <m.majewski2@...sung.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tomasz Figa <tomasz.figa@...il.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 0/4] Fix Samsung pinctrl driver static allocation of GPIO
 base warning

On 08/10/2023 20:45, Sam Protsenko wrote:

>>>
>>> Thank you for handling this! Those deprecation warnings have been
>>> bugging me for some time :) While testing this series on my E850-96
>>> board (Exynos850 based), I noticed some changes in
>>> /sys/kernel/debug/gpio file, like these:
>>>
>>> 8<------------------------------------------------------------------------------------------>8
>>> -gpiochip0: GPIOs 0-7, parent: platform/11850000.pinctrl, gpa0:
>>> - gpio-7   (                    |Volume Up           ) in  hi IRQ ACTIVE LOW
>>> +gpiochip0: GPIOs 512-519, parent: platform/11850000.pinctrl, gpa0:
>>> + gpio-519 (                    |Volume Up           ) in  hi IRQ ACTIVE LOW
>>>
>>> -gpiochip1: GPIOs 8-15, parent: platform/11850000.pinctrl, gpa1:
>>> - gpio-8   (                    |Volume Down         ) in  hi IRQ ACTIVE LOW
>>> +gpiochip1: GPIOs 520-527, parent: platform/11850000.pinctrl, gpa1:
>>> + gpio-520 (                    |Volume Down         ) in  hi IRQ ACTIVE LOW
>>>
>>> -gpiochip2: GPIOs 16-23, parent: platform/11850000.pinctrl, gpa2:
>>> +gpiochip2: GPIOs 528-535, parent: platform/11850000.pinctrl, gpa2:
>>>
>>> ...
>>> 8<------------------------------------------------------------------------------------------>8
>>>
>>> So basically it looks like all line numbers were offset by 512. Can
>>> you please comment on this? Is it an intentional change, and why it's
>>> happening?
>>>
>>> Despite of that change, everything seems to be working fine. But I
>>> kinda liked the numeration starting from 0 better :)
>>
>> Could it be the reason of dynamic allocation?
>>
> 
> I just asked because I didn't know :) But ok, if you want me to do
> some digging... It seems like having GPIO_DYNAMIC_BASE=512 is not
> necessarily the reason of dynamic allocation, but instead just a way
> to keep 0-512 range for legacy GPIO drivers which might use that area
> to allocate GPIO numbers statically. It's mentioned here:
> 
>     /*
>      * At the end we want all GPIOs to be dynamically allocated from 0.
>      * However, some legacy drivers still perform fixed allocation.
>      * Until they are all fixed, leave 0-512 space for them.
>      */
>     #define GPIO_DYNAMIC_BASE    512
> 
> As mentioned in another comment in gpiochip_add_data_with_key(), that
> numberspace shouldn't matter and in the end should go away, as GPIO
> sysfs interface is pretty much deprecated at this point, and everybody
> should stick to GPIO descriptors.
> 
> Anyway, now that it's clear that the base number change was intended
> and shouldn't matter, for all patches in the series:
> 
> Reviewed-by: Sam Protsenko <semen.protsenko@...aro.org>
> Tested-by: Sam Protsenko <semen.protsenko@...aro.org>

If all the GPIOs changed due to switch to dynamic allocation, aren't we
breaking all user-space users?

Best regards,
Krzysztof