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

[Bartosz Golaszewski <brgl@bgdev.pl>]

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.

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,
-- 
Bartosz Golaszewski <bartosz.golaszewski@linaro.org>