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

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

quoted

quoted

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@linaro.org>
Tested-by: Sam Protsenko <semen.protsenko@linaro.org>

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

Best regards,
Krzysztof


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel