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The current voting mechanism in GPIO shared proxy assumes that "low" is
always the default value and users can only vote for driving the GPIO
"high" in which case it will remain high as long as there's at least one
user voting.
This makes it impossible to use the automatic sharing management for
certain use-cases such as the write-protect GPIOs of EEPROMs which are
requested "high" and driven "low" to enable writing. In this case, if
the WP GPIO is shared by multiple EEPROMs, and at least one of them
wants to enable writing, the pin must be set to "low".
Modify the voting heuristic to assume the value set by the first user on
request to be the "default" and subseqent calls to gpiod_set_value()
will constitute votes for a change of the value to the opposite. In the
wp-gpios case it will mean that the nvmem core requests the GPIO as
"out-high" for all EEPROMs sharing the pin, and when one of them wants
to write, the pin will be driven low, enabling it.
Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
Reported-by: Marek Vasut <marex@nabladev.com>
Closes: https://lore.kernel.org/all/20260511163518.51104-1-marex@nabladev.com/
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260630-gpio-shared-dynamic-voting-v3-1-8ecf0542953b@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux
Pull gpio fixes from Bartosz Golaszewski:
- check the return value of gpiochip_add_data() in gpio-mvebu and
gpio-htc-egpio
- avoid locking context issues with GPIO drivers using the shared GPIO
proxy by only allowing sleeping operations (atomic GPIO ops don't
really make sense in shared context anyway)
- with the above: restore non-sleeping GPIO access in pinctrl-meson
- fix return value on OOM in gpio-timberdale
- fix interrupt handling in gpio-mt7621
- support both A and B variants of NCT6126D in gpio-f7188x
* tag 'gpio-fixes-for-v7.2-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux:
pinctrl: meson: restore non-sleeping GPIO access
gpio: timberdale: Return -ENOMEM on dynamic memory allocation in probe
gpio: mt7621: be sure IRQ domain is created before exposing GPIO chips
gpio: mt7621: more robust management of IRQ domain teardown
gpio: mt7621: avoid corruption of shared interrupt trigger state
gpio: shared-proxy: always serialize with a sleeping mutex
gpio-f7188x: Add support for NCT6126D version B
gpio: htc-egpio: use managed gpiochip registration
gpio: mvebu: fail probe if gpiochip registration fails
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files)
Replace the #include of <linux/mod_devicetable.h> by the more specific
<linux/device-id/*.h> where applicable. For most cases the include
can be dropped completely, only a few drivers need one or two headers
added.
Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/1a3f2007c5c5dcf555c09a4035ce3ae8ef1b6c49.1782808461.git.u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König (The Capable Hub) <u.kleine-koenig@baylibre.com>
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The shared GPIO descriptor used either a mutex or a spinlock, chosen at
runtime from the underlying chip's can_sleep:
shared_desc->can_sleep = gpiod_cansleep(shared_desc->desc);
... if (can_sleep) mutex_lock(); else spin_lock_irqsave();
can_sleep describes only the value path (->get/->set). Under the same
lock, however, the proxy may call gpiod_set_config() and
gpiod_direction_*(), which can reach pinctrl paths that take a mutex
(e.g. gpiod_set_config() -> gpiochip_generic_config() ->
pinctrl_gpio_set_config()), independent of can_sleep. On a controller
with non-sleeping MMIO value ops the descriptor lock was a spinlock, so
the sleeping pinctrl call ran from atomic context. Reproduced on an
Amlogic A113X board with the workaround from commit 28f240683871
("pinctrl: meson: mark the GPIO controller as sleeping") reverted; the
original Khadas VIM3 report hit the same path:
BUG: sleeping function called from invalid context
__mutex_lock
pinctrl_get_device_gpio_range
pinctrl_gpio_set_config
gpiochip_generic_config
gpiod_set_config
gpio_shared_proxy_set_config <- voting spinlock held
...
mmc_pwrseq_simple_probe
The spinlock existed to take the value vote from atomic context, but the
vote and the (possibly sleeping) control operations share the same state
and lock, so this scheme cannot serialize config under a mutex and still
offer atomic value access. Always serialize the shared descriptor with a
mutex instead and mark the proxy a sleeping gpiochip, driving the
underlying GPIO through the cansleep value accessors: those are valid
for both sleeping and non-sleeping chips, so value access keeps working
on fast controllers, at the cost of no longer being atomic.
With every vote edge now driven through the cansleep value setter,
gpio_shared_proxy_set_unlocked() no longer needs a per-call setter: drop
its set_func callback and call gpiod_set_value_cansleep() directly. The
shared direction_output path reaches it only once the line is already an
output, so driving the value there is equivalent to re-issuing
gpiod_direction_output(), without the redundant per-edge re-assertion of
drive config and bias.
This is observable: consumers gating on gpiod_cansleep() take their
sleeping branch on a proxied GPIO (mmc-pwrseq-emmc skips its
emergency-restart reset handler; its normal reset is unaffected), and
consumers that reject sleeping GPIOs (pwm-gpio, ps2-gpio, ...) would
fail to probe. Such atomic users do not share a pin through the proxy,
whose purpose is voting on shared reset/enable lines. The same narrowing
already applies on Amlogic since that workaround, and rockchip
addressed the identical splat per-driver in commit 7ca497be0016 ("gpio:
rockchip: Stop calling pinctrl for set_direction"); fixing the proxy
addresses the locking error once, for every controller.
The lock type was added by commit a060b8c511ab ("gpiolib: implement
low-level, shared GPIO support"); the sleeping call under it arrived with
the proxy driver.
Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Closes: https://lore.kernel.org/all/00107523-7737-4b92-a785-14ce4e93b8cb@samsung.com/
Signed-off-by: Viacheslav Bocharov <v@baodeep.com>
Link: https://patch.msgid.link/20260630101545.800625-2-v@baodeep.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
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When the user of a shared GPIO managed by gpio-shared-proxy calls
gpiod_put() to release it, we never undo the potential "vote" for
driving the shared line "high". In the free() callback, check if this
proxy voted for "high" and - if so - decrease the number of votes and
potentially revert the value to low if this is the last user.
Cc: stable@vger.kernel.org
Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
Closes: https://sashiko.dev/#/patchset/20260513-gpio-shared-dynamic-voting-v1-1-8e1c49961b7d%40oss.qualcomm.com
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260522-gpio-shared-free-vote-v3-1-8a4fddc6bedb@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
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User-space must not fiddle with shared-proxy auxiliary devices. Disable
bind/unbind attributes in sysfs.
Link: https://lore.kernel.org/r/20251126191730.66277-1-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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Add a virtual GPIO proxy driver which arbitrates access to a single
shared GPIO by multiple users. It works together with the core shared
GPIO support from GPIOLIB and functions by acquiring a reference to a
shared GPIO descriptor exposed by gpiolib-shared and making sure that
the state of the GPIO stays consistent.
In general: if there's only one user at the moment: allow it to do
anything as if this was a normal GPIO (in essence: just propagate calls
to the underlying real hardware driver). If there are more users: don't
allow to change the direction set by the initial user, allow to change
configuration options but warn about possible conflicts and finally:
treat the output-high value as a reference counted, logical "GPIO
enabled" setting, meaning: the GPIO value is set to high when the first
user requests it to be high and back to low once the last user stops
"voting" for high.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20251112-gpio-shared-v4-4-b51f97b1abd8@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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