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: 7b78b26757e0 ("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: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
index 076d8642675c2723c8938cbd22b1b51014c23871..17343fdc9758402b3cc7c8d61ee908591c977539 100644 (file)
--- a/drivers/gpio/gpiolib-shared.c
+++ b/drivers/gpio/gpiolib-shared.c
@@ -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,