linux.git/drivers/gpio/gpiolib-cdev.c, branch v6.16

gpiolib: don't allow setting values on input lines

2025-04-07T07:00:48+00:00

Some drivers as well as the character device and sysfs code check
whether the line actually is in output mode before allowing the user to
set a value.

However, GPIO value setters now return integer values and can indicate
failures. This allows us to move these checks into the core code.

Reviewed-by: Linus Walleij 
Link: https://lore.kernel.org/r/20250311-gpio-set-check-output-v1-1-d971bca9e6fa@linaro.org
Signed-off-by: Bartosz Golaszewski

gpio: cdev: use raw notifier for line state events

2025-03-13T08:20:12+00:00

We use a notifier to implement the mechanism of informing the user-space
about changes in GPIO line status. We register with the notifier when
the GPIO character device file is opened and unregister when the last
reference to the associated file descriptor is dropped.

Since commit fcc8b637c542 ("gpiolib: switch the line state notifier to
atomic") we use the atomic notifier variant. Atomic notifiers call
rcu_synchronize in atomic_notifier_chain_unregister() which caused a
significant performance regression in some circumstances, observed by
user-space when calling close() on the GPIO device file descriptor.

Replace the atomic notifier with the raw variant and provide
synchronization with a read-write spinlock.

Fixes: fcc8b637c542 ("gpiolib: switch the line state notifier to atomic")
Reported-by: David Jander 
Closes: https://lore.kernel.org/all/20250311110034.53959031@erd003.prtnl/
Tested-by: David Jander 
Tested-by: Kent Gibson 
Link: https://lore.kernel.org/r/20250311-gpiolib-line-state-raw-notifier-v2-1-138374581e1e@linaro.org
Signed-off-by: Bartosz Golaszewski

gpiolib: cdev: use !mem_is_zero() instead of memchr_inv(s, 0, n)

2024-11-12T08:46:17+00:00

Use the mem_is_zero() helper where possible.

Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20241110201706.16614-1-andy.shevchenko@gmail.com
Signed-off-by: Bartosz Golaszewski

gpio: cdev: don't report GPIOs requested as interrupts as used

2024-11-04T08:08:11+00:00

GPIOs used as shared irqs can still be requested by user-space (or
kernel drivers for that matter) yet we report them as used over the
chardev ABI. Drop the test for FLAG_USED_AS_IRQ from
gpio_desc_to_lineinfo().

Reviewed-by: Kent Gibson 
Reviewed-by: Linus Walleij 
Link: https://lore.kernel.org/r/20241031200842.22712-1-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski

gpiolib: avoid format string weakness in workqueue interface

2024-10-31T12:43:09+00:00

Using a string literal as a format string is a possible bug when the
string contains '%' characters:

drivers/gpio/gpiolib-cdev.c:2813:48: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
 2813 |         gdev->line_state_wq = alloc_ordered_workqueue(dev_name(&gdev->dev),
      |                                                       ^~~~~~~~~~~~~~~~~~~~
drivers/gpio/gpiolib-cdev.c:2813:48: note: treat the string as an argument to avoid this
 2813 |         gdev->line_state_wq = alloc_ordered_workqueue(dev_name(&gdev->dev),
      |                                                       ^
      |                                                       "%s",

Do as clang suggests and use a trivial "%s" format string.

Fixes: 7b9b77a8bba9 ("gpiolib: add a per-gpio_device line state notification workqueue")
Signed-off-by: Arnd Bergmann 
Link: https://lore.kernel.org/r/20241028142152.750650-1-arnd@kernel.org
Signed-off-by: Bartosz Golaszewski

gpiolib: cdev: remove redundant store of debounce_period_us

2024-10-22T07:15:30+00:00

debounce_setup() stores the debounce_period_us if the driver supports
debounce, but the debounce_period_us is also stored where debounce_setup()
is called, independent of whether the debounce is being perfomed by
hardware or software.

Remove the redundant storing of the debounce_period_us in
debounce_setup().

Signed-off-by: Kent Gibson 
Link: https://lore.kernel.org/r/20241020115238.170994-1-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski

gpiolib: notify user-space about in-kernel line state changes

2024-10-22T06:59:09+00:00

We currently only notify user-space about line config changes that are
made from user-space. Any kernel config changes are not signalled.

Let's improve the situation by emitting the events closer to the source.
To that end let's call the relevant notifier chain from the functions
setting direction, gpiod_set_config(), gpiod_set_consumer_name() and
gpiod_toggle_active_low(). This covers all the options that we can
inform the user-space about. We ignore events which don't have
corresponding flags exported to user-space on purpose - otherwise the
user would see a config-changed event but the associated line-info would
remain unchanged.

gpiod_direction_output/input() can be called from any context.
Fortunately, we now emit line state events using an atomic notifier
chain, so it's no longer an issue.

Let's also add non-notifying wrappers around the direction setters in
order to not emit superfluous reconfigure events when requesting the
lines as the initial config should be part of the request notification.

Use gpio_do_set_config() instead of gpiod_set_debounce() for configuring
debouncing via hardware from the character device code to avoid multiple
reconfigure events.

Reviewed-by: Kent Gibson 
Link: https://lore.kernel.org/r/20241018-gpio-notify-in-kernel-events-v5-8-c79135e58a1c@linaro.org
Signed-off-by: Bartosz Golaszewski

gpiolib: switch the line state notifier to atomic

2024-10-22T06:59:09+00:00

With everything else ready, we can now switch to using the atomic
notifier for line state events which will allow us to notify user-space
about direction changes from atomic context.

Reviewed-by: Kent Gibson 
Link: https://lore.kernel.org/r/20241018-gpio-notify-in-kernel-events-v5-7-c79135e58a1c@linaro.org
Signed-off-by: Bartosz Golaszewski

gpio: cdev: put emitting the line state events on a workqueue

2024-10-22T06:59:09+00:00

In order to allow line state notifications to be emitted from atomic
context (for instance: from gpiod_direction_input/output()), we must
stop calling any sleeping functions in lineinfo_changed_notify(). To
that end let's use the new workqueue.

Let's atomically allocate small structures containing the required data
and fill it with information immediately upon being notified about the
change except for the pinctrl state which will be retrieved later from
process context. We can pretty reliably do this as pin functions are
typically set once per boot.

Let's make sure to bump the reference count of GPIO device and the GPIO
character device file descriptor to keep both alive until the event was
queued.

Reviewed-by: Kent Gibson 
Link: https://lore.kernel.org/r/20241018-gpio-notify-in-kernel-events-v5-6-c79135e58a1c@linaro.org
Signed-off-by: Bartosz Golaszewski

gpiolib: add a per-gpio_device line state notification workqueue

2024-10-22T06:59:08+00:00

In order to prepare the line state notification mechanism for working in
atomic context as well, add a dedicated, high-priority, ordered
workqueue to GPIO device which will be used to queue the events fron any
context for them to be emitted always in process context.

Reviewed-by: Kent Gibson 
Link: https://lore.kernel.org/r/20241018-gpio-notify-in-kernel-events-v5-5-c79135e58a1c@linaro.org
Signed-off-by: Bartosz Golaszewski