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

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 <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20241018-gpio-notify-in-kernel-events-v5-8-c79135e58a1c@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index a54be597d21a..83690f72f7e5 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -155,6 +155,8 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 int gpiod_set_transitory(struct gpio_desc *desc, bool transitory);
 
 void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action);
+int gpiod_direction_output_nonotify(struct gpio_desc *desc, int value);
+int gpiod_direction_input_nonotify(struct gpio_desc *desc);
 
 struct gpio_desc_label {
 	struct rcu_head rh;
@@ -258,6 +260,7 @@ struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 					 const char *label,
 					 bool platform_lookup_allowed);
 
+int gpio_do_set_config(struct gpio_desc *desc, unsigned long config);
 int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
 		unsigned long lflags, enum gpiod_flags dflags);
 int gpio_set_debounce_timeout(struct gpio_desc *desc, unsigned int debounce);