Re: [PATCH v5 00/15] pinctrl: introduce the concept of a GPIO pin function category

[Linus Walleij <linus.walleij@linaro.org>]

On Fri, Aug 15, 2025 at 11:09 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> Problem: when pinctrl core binds pins to a consumer device and the
> pinmux ops of the underlying driver are marked as strict, the pin in
> question can no longer be requested as a GPIO using the GPIO descriptor
> API. It will result in the following error:
>
> [    5.095688] sc8280xp-tlmm f100000.pinctrl: pin GPIO_25 already requested by regulator-edp-3p3; cannot claim for f100000.pinctrl:570
> [    5.107822] sc8280xp-tlmm f100000.pinctrl: error -EINVAL: pin-25 (f100000.pinctrl:570)
>
> This typically makes sense except when the pins are muxed to a function
> that actually says "GPIO". Of course, the function name is just a string
> so it has no meaning to the pinctrl subsystem.
>
> We have many Qualcomm SoCs (and I can imagine it's a common pattern in
> other platforms as well) where we mux a pin to "gpio" function using the
> `pinctrl-X` property in order to configure bias or drive-strength and
> then access it using the gpiod API. This makes it impossible to mark the
> pin controller module as "strict".
>
> This series proposes to introduce a concept of a sub-category of
> pinfunctions: GPIO functions where the above is not true and the pin
> muxed as a GPIO can still be accessed via the GPIO consumer API even for
> strict pinmuxers.
>
> To that end: we first clean up the drivers that use struct function_desc
> and make them use the smaller struct pinfunction instead - which is the
> correct structure for drivers to describe their pin functions with. We
> also rework pinmux core to not duplicate memory used to store the
> pinfunctions unless they're allocated dynamically.
>
> First: provide the kmemdup_const() helper which only duplicates memory
> if it's not in the .rodata section. Then rework all pinctrl drivers that
> instantiate objects of type struct function_desc as they should only be
> created by pinmux core. Next constify the return value of the accessor
> used to expose these structures to users and finally convert the
> pinfunction object within struct function_desc to a pointer and use
> kmemdup_const() to assign it. With this done proceed to add
> infrastructure for the GPIO pin function category and use it in Qualcomm
> drivers. At the very end: make the Qualcomm pinmuxer strict.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
(...)
> Bartosz Golaszewski (15):
>       devres: provide devm_kmemdup_const()
>       pinctrl: ingenic: use struct pinfunction instead of struct function_desc
>       pinctrl: airoha: replace struct function_desc with struct pinfunction
>       pinctrl: mediatek: mt7988: use PINCTRL_PIN_FUNCTION()
>       pinctrl: mediatek: moore: replace struct function_desc with struct pinfunction
>       pinctrl: imx: don't access the pin function radix tree directly
>       pinctrl: keembay: release allocated memory in detach path
>       pinctrl: keembay: use a dedicated structure for the pinfunction description
>       pinctrl: constify pinmux_generic_get_function()
>       pinctrl: make struct pinfunction a pointer in struct function_desc
>       pinctrl: qcom: use generic pin function helpers
>       pinctrl: allow to mark pin functions as requestable GPIOs

I applied these 12 patches as a starter so they can
stabilize in linux-next.

>       pinctrl: qcom: add infrastructure for marking pin functions as GPIOs
>       pinctrl: qcom: mark the `gpio` and `egpio` pins function as non-strict functions
>       pinctrl: qcom: make the pinmuxing strict

Neil reports of regressions on qcom platforms so I assume it's something
in the last three patches that's causing it and I hold these three off
until you have time to look at it (and focus at just the final qcom pieces).

Yours,
Linus Walleij