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

From: Linus Walleij <linusw@kernel.org>
To: Viacheslav Bocharov <v@baodeep.com>
Cc: Bartosz Golaszewski <brgl@kernel.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	 Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	 Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	 Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	 Diederik de Haas <diederik@cknow-tech.com>,
	linux-gpio@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	linux-amlogic@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] pinctrl: meson: restore non-sleeping GPIO access
Date: Wed, 1 Jul 2026 00:31:34 +0200	[thread overview]
Message-ID: <CAD++jLmprP3Ur_BFB9K_we3wdRkZ7dqX3vX-4mPOZZD7WujxJA@mail.gmail.com> (raw)
In-Reply-To: <20260625115718.1678991-3-v@baodeep.com>

On Thu, Jun 25, 2026 at 1:58 PM Viacheslav Bocharov <v@baodeep.com> 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/20260105150509.56537-1-bartosz.golaszewski@oss.qualcomm.com/
> Signed-off-by: Viacheslav Bocharov <v@baodeep.com>

Acked-by: Linus Walleij <linusw@kernel.org>

Yours,
Linus Walleij

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