Re: [PATCH v2 2/2] pinctrl: meson: restore non-sleeping GPIO access

On Thu, Jun 25, 2026 at 1:58 PM Viacheslav Bocharov <[email protected]> wrote:

> Commit 28f240683871 ("pinctrl: meson: mark the GPIO controller as
> sleeping") set gpio_chip.can_sleep = true to work around
> gpio-shared-proxy holding a spinlock across a sleeping pinctrl config
> path. That locking bug is now fixed in the shared-proxy itself ("gpio:
> shared-proxy: always serialize with a sleeping mutex"), so the
> controller-wide workaround is no longer needed; the meson GPIO
> controller does not sleep.
>
> meson_gpio_get/set/direction_* access MMIO through regmap. The
> regmap_mmio bus uses fast I/O (spinlock) locking, so these value
> callbacks do not contain sleeping operations. Since gpio_chip.can_sleep
> describes the get/set value path, restore can_sleep = false.
>
> Marking the controller sleeping also broke atomic value consumers such
> as w1-gpio (1-Wire bitbang): w1_io.c runs its read time slot under
> local_irq_save() and uses the non-cansleep gpiod_set_value() /
> gpiod_get_value(), which with can_sleep=true trigger WARN_ON(can_sleep)
> in gpiolib on every transferred bit (from w1_gpio_write_bit() /
> w1_gpio_read_bit() via w1_reset_bus() and w1_search()). The printk and
> stack dump inside the IRQs-off, microsecond-scale time slot destroy the
> bit timing, so reset/presence detection and ROM search fail: the bus
> master registers but w1_master_slave_count stays at 0 and no devices
> are found. Verified on an Amlogic A113X board (DS18B20 on GPIOA_14):
> with can_sleep restored to false the warnings are gone and the sensor
> is detected and read again.
>
> This must not be applied or backported without the shared-proxy locking
> fix above; otherwise the original Khadas VIM3 splat returns on boards
> that genuinely share a meson GPIO.
>
> Fixes: 28f240683871 ("pinctrl: meson: mark the GPIO controller as sleeping")
> Link: https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Viacheslav Bocharov <[email protected]>

Acked-by: Linus Walleij <[email protected]>

Yours,
Linus Walleij

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