[PATCH v2 10/11] gpio: Leverage revocable for accessing struct gpio_chip

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

Struct gpio_device now provides a revocable provider to the underlying
struct gpio_chip.  Leverage revocable for accessing the struct
gpio_chip.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
v2:
- Separate from v1(a) for excluding gpio_chip_guard and combine v1(b).

v1(a):
- https://lore.kernel.org/all/20260116081036.352286-23-tzungbi@kernel.org
v1(b):
- https://lore.kernel.org/all/20260116081036.352286-19-tzungbi@kernel.org

 drivers/gpio/gpiolib.c | 52 +++++++++++++++---------------------------
 1 file changed, 18 insertions(+), 34 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e62b00191d59..347ff456858f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -338,7 +338,10 @@ EXPORT_SYMBOL(gpio_device_get_label);
  */
 struct gpio_chip *gpio_device_get_chip(struct gpio_device *gdev)
 {
-	return rcu_dereference_check(gdev->chip, 1);
+	struct gpio_chip *gc;
+
+	REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
+	return gc;
 }
 EXPORT_SYMBOL_GPL(gpio_device_get_chip);
 
@@ -558,9 +561,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
 
 	list_for_each_entry_srcu(gdev, &gpio_devices, list,
 				 srcu_read_lock_held(&gpio_devices_srcu)) {
-		guard(srcu)(&gdev->srcu);
-
-		gc = srcu_dereference(gdev->chip, &gdev->srcu);
+		REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
 		if (!gc)
 			continue;
 
@@ -972,9 +973,7 @@ static void gpiochip_setup_devs(void)
 
 	list_for_each_entry_srcu(gdev, &gpio_devices, list,
 				 srcu_read_lock_held(&gpio_devices_srcu)) {
-		guard(srcu)(&gdev->srcu);
-
-		gc = srcu_dereference(gdev->chip, &gdev->srcu);
+		REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
 		if (!gc) {
 			dev_err(&gdev->dev, "Underlying GPIO chip is gone\n");
 			continue;
@@ -1379,11 +1378,11 @@ struct gpio_device *gpio_device_find(const void *data,
 		if (!device_is_registered(&gdev->dev))
 			continue;
 
-		guard(srcu)(&gdev->srcu);
-
-		gc = srcu_dereference(gdev->chip, &gdev->srcu);
+		REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
+		if (!gc)
+			continue;
 
-		if (gc && match(gc, data))
+		if (match(gc, data))
 			return gpio_device_get(gdev);
 	}
 
@@ -3325,16 +3324,10 @@ static int gpio_chip_get_value(struct gpio_chip *gc, const struct gpio_desc *des
 
 static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 {
-	struct gpio_device *gdev;
 	struct gpio_chip *gc;
 	int value;
 
-	/* FIXME Unable to use gpio_chip_guard due to const desc. */
-	gdev = desc->gdev;
-
-	guard(srcu)(&gdev->srcu);
-
-	gc = srcu_dereference(gdev->chip, &gdev->srcu);
+	REVOCABLE_TRY_ACCESS_WITH(desc->gdev->chip_rp, gc);
 	if (!gc)
 		return -ENODEV;
 
@@ -3375,9 +3368,10 @@ static int gpio_chip_get_multiple(struct gpio_chip *gc,
 /* The 'other' chip must be protected with its GPIO device's SRCU. */
 static bool gpio_device_chip_cmp(struct gpio_device *gdev, struct gpio_chip *gc)
 {
-	guard(srcu)(&gdev->srcu);
+	struct gpio_chip *chip;
 
-	return gc == srcu_dereference(gdev->chip, &gdev->srcu);
+	REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, chip);
+	return chip ? chip == gc : false;
 }
 
 int gpiod_get_array_value_complex(bool raw, bool can_sleep,
@@ -3400,9 +3394,7 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
 		if (!can_sleep)
 			WARN_ON(array_info->gdev->can_sleep);
 
-		guard(srcu)(&array_info->gdev->srcu);
-		gc = srcu_dereference(array_info->gdev->chip,
-				      &array_info->gdev->srcu);
+		REVOCABLE_TRY_ACCESS_WITH(array_info->gdev->chip_rp, gc);
 		if (!gc)
 			return -ENODEV;
 
@@ -3749,9 +3741,7 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
 				return -EPERM;
 		}
 
-		guard(srcu)(&array_info->gdev->srcu);
-		gc = srcu_dereference(array_info->gdev->chip,
-				      &array_info->gdev->srcu);
+		REVOCABLE_TRY_ACCESS_WITH(array_info->gdev->chip_rp, gc);
 		if (!gc)
 			return -ENODEV;
 
@@ -4049,7 +4039,6 @@ EXPORT_SYMBOL_GPL(gpiod_is_shared);
  */
 int gpiod_to_irq(const struct gpio_desc *desc)
 {
-	struct gpio_device *gdev;
 	struct gpio_chip *gc;
 	int offset;
 	int ret;
@@ -4058,10 +4047,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 	if (ret <= 0)
 		return -EINVAL;
 
-	gdev = desc->gdev;
-	/* FIXME Cannot use gpio_chip_guard due to const desc. */
-	guard(srcu)(&gdev->srcu);
-	gc = srcu_dereference(gdev->chip, &gdev->srcu);
+	REVOCABLE_TRY_ACCESS_WITH(desc->gdev->chip_rp, gc);
 	if (!gc)
 		return -ENODEV;
 
@@ -5440,9 +5426,7 @@ static int gpiolib_seq_show(struct seq_file *s, void *v)
 	if (priv->newline)
 		seq_putc(s, '\n');
 
-	guard(srcu)(&gdev->srcu);
-
-	gc = srcu_dereference(gdev->chip, &gdev->srcu);
+	REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
 	if (!gc) {
 		seq_printf(s, "%s: (dangling chip)\n", dev_name(&gdev->dev));
 		return 0;
-- 
2.53.0.rc2.204.g2597b5adb4-goog