[PATCH v3 0/2] gpio: fix sleeping-in-atomic in shared-proxy; restore meson non-sleeping

gpio-shared-proxy chooses its descriptor lock (mutex vs spinlock) from
the underlying chip's can_sleep, but under that lock it calls config and
direction ops that reach sleeping pinctrl paths. On a controller with
non-sleeping MMIO value ops the lock is a spinlock, so a sleeping call
runs from atomic context:

  BUG: sleeping function called from invalid context
    ... pinctrl_gpio_set_config <- gpiochip_generic_config
    <- gpio_shared_proxy_set_config (voting spinlock held)
    <- ... <- mmc_pwrseq_simple_probe

This was reported on Khadas VIM3 and worked around for Amlogic by
commit 28f240683871 ("pinctrl: meson: mark the GPIO controller as
sleeping"), which marked the whole meson controller sleeping. That
workaround broke atomic value-path consumers: w1-gpio (1-Wire bitbang)
no longer detects devices, because its IRQ-disabled read slot calls the
non-cansleep gpiod_*_value() and now hits WARN_ON(can_sleep) per bit.

Patch 1 fixes the proxy locking generically (always a sleeping mutex).
Patch 2 then restores meson can_sleep=false, fixing 1-Wire.

Patch 1 has a trade-off: a proxied GPIO becomes sleeping, so consumers
gating on gpiod_cansleep() change behaviour. No current device needs
atomic (non-cansleep) value access on a shared GPIO -- every report
(Khadas VIM3, ODROID-M1, my test on JetHub D1+) is a shared reset line
(eMMC/SDIO pwrseq or PCIe reset) driven through the cansleep accessors,
which is what the proxy exists to vote on; bit-banging that needs atomic
access cannot work through voting anyway. An alternative that keeps
atomic value access (split locking) is possible but adds a second lock
and new race windows, so this series takes the simpler mutex-only
approach.

The two are a unit: patch 2 must not be applied without patch 1,
otherwise the original VIM3 splat returns on boards that share a meson
GPIO -- please keep the order. I have not Cc'd stable; I will request
stable backports separately once both patches have landed.

Changes since v2:
- gpio: shared-proxy: drop the set_func callback from
  gpio_shared_proxy_set_unlocked() and call gpiod_set_value_cansleep()
  directly. The shared direction_output path drives the already-output
  line through the value setter instead of re-issuing
  gpiod_direction_output() (equivalent, minus a redundant per-edge
  re-assert of drive config/bias). No change to the voting/value
  behaviour.

Changes since v1:
- gpio: shared-proxy: open-code the descriptor mutex; drop the
  gpio_shared_desc_lock guard and the gpio_shared_lockdep_assert()
  helper, move the mutex rationale to the can_sleep assignment.

v1: https://lore.kernel.org/linux-gpio/[email protected]/
v2: https://lore.kernel.org/linux-gpio/[email protected]/

Viacheslav Bocharov (2):
  gpio: shared-proxy: always serialize with a sleeping mutex
  pinctrl: meson: restore non-sleeping GPIO access

 drivers/gpio/gpio-shared-proxy.c      | 76 ++++++++++-----------------
 drivers/gpio/gpiolib-shared.c         |  9 +---
 drivers/gpio/gpiolib-shared.h         | 28 +---------
 drivers/pinctrl/meson/pinctrl-meson.c |  2 +-
 4 files changed, 33 insertions(+), 82 deletions(-)


base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
-- 
2.54.0

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