[PATCH v2 07/11] gpio: Add revocable provider handle for struct gpio_chip

[Tzung-Bi Shih <tzungbi@kernel.org>]

The underlying chip can be removed asynchronously.  `gdev->srcu` is used
to ensure the synchronization before accessing `gdev->chip`.

Revocable encapsulates the details.  Add revocable provider handle for
the corresponding struct gpio_chip in struct gpio_device so that it can
start to hide the synchronization details.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
v2:
- Change usages accordingly after applying
  https://lore.kernel.org/all/20260129143733.45618-2-tzungbi@kernel.org.
  - Add __rcu for `chip_rp`.
  - Pass pointer of pointer to revocable_provider_revoke().
- Rebase accordingly after applying
  https://lore.kernel.org/all/20260203060210.972243-1-tzungbi@kernel.org.

v1: https://lore.kernel.org/all/20260116081036.352286-13-tzungbi@kernel.org

 drivers/gpio/gpiolib.c | 20 ++++++++++++++++++--
 drivers/gpio/gpiolib.h |  2 ++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 7885dcd1e49d..fdae10ec3a17 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -22,6 +22,7 @@
 #include <linux/nospec.h>
 #include <linux/of.h>
 #include <linux/pinctrl/consumer.h>
+#include <linux/revocable.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/srcu.h>
@@ -1110,6 +1111,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		goto err_put_device;
 	}
 
+	gdev->chip_rp = revocable_provider_alloc(gc);
+	if (!gdev->chip_rp) {
+		ret = -ENOMEM;
+		goto err_put_device;
+	}
+
 	gdev->can_sleep = gc->can_sleep;
 	rwlock_init(&gdev->line_state_lock);
 	RAW_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
@@ -1139,7 +1146,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			if (base < 0) {
 				ret = base;
 				base = 0;
-				goto err_put_device;
+				goto err_free_rp;
 			}
 
 			/*
@@ -1159,7 +1166,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		ret = gpiodev_add_to_list_unlocked(gdev);
 		if (ret) {
 			gpiochip_err(gc, "GPIO integer space overlap, cannot add chip\n");
-			goto err_put_device;
+			goto err_free_rp;
 		}
 	}
 
@@ -1256,6 +1263,14 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	scoped_guard(mutex, &gpio_devices_lock)
 		list_del_rcu(&gdev->list);
 	synchronize_srcu(&gpio_devices_srcu);
+err_free_rp:
+	/*
+	 * Unlike other allocated resources for `gdev` can be freed
+	 * in gpiodev_release().  Call revocable_provider_revoke()
+	 * here as it's designed to be called when the chip is gone
+	 * (i.e., gpiochip_remove()).
+	 */
+	revocable_provider_revoke(&gdev->chip_rp);
 err_put_device:
 	gpio_device_put(gdev);
 	goto err_print_message;
@@ -1302,6 +1317,7 @@ void gpiochip_remove(struct gpio_chip *gc)
 	/* Numb the device, cancelling all outstanding operations */
 	rcu_assign_pointer(gdev->chip, NULL);
 	synchronize_srcu(&gdev->srcu);
+	revocable_provider_revoke(&gdev->chip_rp);
 	gpio_device_teardown_shared(gdev);
 	gpiochip_irqchip_remove(gc);
 	acpi_gpiochip_remove(gc);
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 3abb90385829..cd136d5b52e9 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -52,6 +52,7 @@
  * @device_notifier: used to notify character device wait queues about the GPIO
  *                   device being unregistered
  * @srcu: protects the pointer to the underlying GPIO chip
+ * @chip_rp: revocable provider handle for the corresponding struct gpio_chip.
  * @pin_ranges: range of pins served by the GPIO driver
  *
  * This state container holds most of the runtime variable data
@@ -79,6 +80,7 @@ struct gpio_device {
 	struct workqueue_struct	*line_state_wq;
 	struct blocking_notifier_head device_notifier;
 	struct srcu_struct	srcu;
+	struct revocable_provider __rcu *chip_rp;
 
 #ifdef CONFIG_PINCTRL
 	/*
-- 
2.53.0.rc2.204.g2597b5adb4-goog