Commit d578b318 authored by Bartosz Golaszewski's avatar Bartosz Golaszewski
Browse files

gpio: shared: fix a false-positive sharing detection with reset-gpios 

After scanning the devicetree, we remove all entries that have only one
reference, while creating GPIO shared proxies for the remaining, shared
entries. However: for the reset-gpio corner-case, we will have two
references for a "reset-gpios" pin that's not really shared. In this
case one will come from the actual consumer fwnode and the other from
the potential auxiliary reset-gpio device. This causes the GPIO core to
create unnecessary GPIO shared proxy devices for pins that are not
really shared.

Add a function that can detect this situation and remove entries that
have exactly two references but one of them is a reset-gpio.

Fixes: 7b78b267 ("gpio: shared: handle the reset-gpios corner case")
Link: https://lore.kernel.org/r/20260108-gpio-shared-false-positive-v1-1-5dbf8d1b2f7d@oss.qualcomm.com


Signed-off-by: default avatarBartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
parent 36f597bb

drivers/gpio/gpiolib-shared.c

+32 −2
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ struct gpio_shared_ref { 
	struct lock_class_key lock_key;

	struct auxiliary_device adev;

	struct gpiod_lookup_table *lookup;

	bool is_reset_gpio;

};



/* Represents a single GPIO pin. */
@@ -112,7 +113,8 @@ static int gpio_shared_setup_reset_proxy(struct gpio_shared_entry *entry, 
	struct gpio_shared_ref *ref;



	list_for_each_entry(ref, &entry->refs, list) {

		if (!ref->fwnode && ref->con_id && strcmp(ref->con_id, "reset") == 0)

		if (ref->is_reset_gpio)

			/* Already set-up. */

			return 0;

	}
@@ -120,6 +122,8 @@ static int gpio_shared_setup_reset_proxy(struct gpio_shared_entry *entry, 
	if (!ref)

		return -ENOMEM;



	ref->is_reset_gpio = true;



	list_add_tail(&ref->list, &entry->refs);



	pr_debug("Created a secondary shared GPIO reference for potential reset-gpio device for GPIO %u at %s\n",
@@ -714,12 +718,38 @@ static void __init gpio_shared_teardown(void) 
	}

}



static bool gpio_shared_entry_is_really_shared(struct gpio_shared_entry *entry)

{

	size_t num_nodes = list_count_nodes(&entry->refs);

	struct gpio_shared_ref *ref;



	if (num_nodes <= 1)

		return false;



	if (num_nodes > 2)

		return true;



	/* Exactly two references: */

	list_for_each_entry(ref, &entry->refs, list) {

		/*

		 * Corner-case: the second reference comes from the potential

		 * reset-gpio instance. However, this pin is not really shared

		 * as it would have three references in this case. Avoid

		 * creating unnecessary proxies.

		 */

		if (ref->is_reset_gpio)

			return false;

	}



	return true;

}



static void gpio_shared_free_exclusive(void)

{

	struct gpio_shared_entry *entry, *epos;



	list_for_each_entry_safe(entry, epos, &gpio_shared_list, list) {

		if (list_count_nodes(&entry->refs) > 1)

		if (gpio_shared_entry_is_really_shared(entry))

			continue;



		gpio_shared_drop_ref(list_first_entry(&entry->refs,