[PATCH 12/23] gpiolib: 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 in a neat way.  Add revocable
provider handle for the corresponding struct gpio_chip in struct
gpio_device so that we can start to hide the synchronization details.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
 drivers/gpio/gpiolib.c | 19 +++++++++++++++++++
 drivers/gpio/gpiolib.h |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index efe72b81e131..6226dc738281 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>
@@ -1105,6 +1106,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	if (ret)
 		goto err_cleanup_gdev_srcu;
 
+	gdev->chip_rp = revocable_provider_alloc(gc);
+	if (!gdev->chip_rp) {
+		ret = -ENOMEM;
+		goto err_cleanup_desc_srcu;
+	}
+
 	device_initialize(&gdev->dev);
 	/* From this point, the .release() function cleans up gdev->dev */
 	gdev->dev.type = &gpio_dev_type;
@@ -1258,9 +1265,20 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		list_del_rcu(&gdev->list);
 	synchronize_srcu(&gpio_devices_srcu);
 err_put_device:
+	/*
+	 * Error handling of the revocable provider is tricky.  Unlike other
+	 * allocated resources for `gdev` are freed in gpiodev_release().
+	 * We need to call revocable_provider_revoke() here as it's designed
+	 * to be called when the chip is gone (i.e. gpiochip_remove()).
+	 *
+	 * Note: must before gpio_device_put() as it frees `gdev`.
+	 */
+	revocable_provider_revoke(gdev->chip_rp);
 	gpio_device_put(gdev);
 	goto err_print_message;
 
+err_cleanup_desc_srcu:
+	cleanup_srcu_struct(&gdev->desc_srcu);
 err_cleanup_gdev_srcu:
 	cleanup_srcu_struct(&gdev->srcu);
 err_free_label:
@@ -1307,6 +1325,7 @@ 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 77f6f2936dc2..e61db3a75e84 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 *chip_rp;
 
 #ifdef CONFIG_PINCTRL
 	/*
-- 
2.52.0.457.g6b5491de43-goog