Re: [PATCH v2 00/10] gpio: improve support for shared GPIOs

["Péter Ujfalusi" <peter.ujfalusi@linux.intel.com>]

On 22/10/2025 16:10, Bartosz Golaszewski wrote:
> Problem statement: GPIOs are implemented as a strictly exclusive
> resource in the kernel but there are lots of platforms on which single
> pin is shared by multiple devices which don't communicate so need some
> way of properly sharing access to a GPIO. What we have now is the
> GPIOD_FLAGS_BIT_NONEXCLUSIVE flag which was introduced as a hack and
> doesn't do any locking or arbitration of access - it literally just hand
> the same GPIO descriptor to all interested users.

I had few stabs on this in the past, all got somehow derailed, one
example was:
https://lkml.org/lkml/2019/10/30/311

> The proposed solution is composed of three major parts: the high-level,
> shared GPIO proxy driver that arbitrates access to the shared pin and
> exposes a regular GPIO chip interface to consumers, a low-level shared
> GPIOLIB module that scans firmware nodes and creates auxiliary devices
> that attach to the proxy driver and finally a set of core GPIOLIB
> changes that plug the former into the GPIO lookup path.
> 
> The changes are implemented in a way that allows to seamlessly compile
> out any code related to sharing GPIOs for systems that don't need it.
> 
> The practical use-case for this are the powerdown GPIOs shared by
> speakers on Qualcomm db845c platform, however I have also extensively
> tested it using gpio-virtuser on arm64 qemu with various DT
> configurations.
> 
> I'm Cc'ing some people that may help with reviewing/be interested in
> this: OF maintainers (because the main target are OF systems initially),
> Mark Brown because most users of GPIOD_FLAGS_BIT_NONEXCLUSIVE live
> in audio or regulator drivers and one of the goals of this series is
> dropping the hand-crafted GPIO enable counting via struct
> regulator_enable_gpio in regulator core), Andy and Mika because I'd like
> to also cover ACPI (even though I don't know about any ACPI platform that
> would need this at the moment, I think it makes sense to make the
> solution complete), Dmitry (same thing but for software nodes), Mani
> (because you have a somewhat related use-case for the PERST# signal and
> I'd like to hear your input on whether this is something you can use or
> maybe it needs a separate, implicit gpio-perst driver similar to what
> Krzysztof did for reset-gpios) and Greg (because I mentioned this to you
> last week in person and I also use the auxiliary bus for the proxy
> devices).
> 
> Merging strategy: patches 1-6 should go through the GPIO tree and then
> ARM-SoC, ASoC and regulator trees can pull these changes from an
> immutable branch and apply the remaining patches.
> 
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> ---
> Changes in v2:
> - Fix a memory leak in error path in gpiolib-shared
> - Drop the gpio-wcd934x fix that already went upstream
> - Free resources used during scanning by GPIOs that turned out to be
>   unique
> - Rework the OF property scanning
> - Add patches making the regulator subsystem aware of shared GPIOs
>   managed by GPIOLIB
> - Link to v1: https://lore.kernel.org/r/20250924-gpio-shared-v1-0-775e7efeb1a3@linaro.org
> 
> ---
> Bartosz Golaszewski (10):
>       string: provide strends()
>       gpiolib: define GPIOD_FLAG_SHARED
>       gpiolib: implement low-level, shared GPIO support
>       gpio: shared-proxy: implement the shared GPIO proxy driver
>       gpiolib: support shared GPIOs in core subsystem code
>       gpio: provide gpiod_is_shared()
>       arm64: select HAVE_SHARED_GPIOS for ARCH_QCOM
>       ASoC: wsa881x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
>       ASoC: wsa883x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
>       regulator: make the subsystem aware of shared GPIOs
> 
>  arch/arm64/Kconfig.platforms     |   1 +
>  drivers/gpio/Kconfig             |  17 ++
>  drivers/gpio/Makefile            |   2 +
>  drivers/gpio/gpio-shared-proxy.c | 329 ++++++++++++++++++++++++
>  drivers/gpio/gpiolib-shared.c    | 530 +++++++++++++++++++++++++++++++++++++++
>  drivers/gpio/gpiolib-shared.h    |  71 ++++++
>  drivers/gpio/gpiolib.c           |  70 +++++-
>  drivers/gpio/gpiolib.h           |   2 +
>  drivers/regulator/core.c         |   8 +
>  include/linux/gpio/consumer.h    |   9 +
>  include/linux/string.h           |   2 +
>  lib/string.c                     |  19 ++
>  lib/tests/string_kunit.c         |  13 +
>  sound/soc/codecs/wsa881x.c       |   3 +-
>  sound/soc/codecs/wsa883x.c       |   7 +-
>  15 files changed, 1067 insertions(+), 16 deletions(-)
> ---
> base-commit: 304d18863e6e62a8f2d0350ce0a59596e2e42768
> change-id: 20250908-gpio-shared-67ec352884b6
> 
> Best regards,

-- 
Péter