[PATCH v2 08/11] gpio: cdev: 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:
- Change usages accordingly after applying
  https://lore.kernel.org/all/20260129143733.45618-4-tzungbi@kernel.org.
  - Preserve a local storage for `struct revocable`.
- Combine multiple patches (see "v1:").

v1:
- https://lore.kernel.org/all/20260116081036.352286-14-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-15-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-16-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-17-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-18-tzungbi@kernel.org

 drivers/gpio/gpiolib-cdev.c | 70 ++++++++++++++++++-------------------
 1 file changed, 34 insertions(+), 36 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index aaa5de814468..ca9c04765df4 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -22,6 +22,7 @@
 #include <linux/overflow.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/poll.h>
+#include <linux/revocable.h>
 #include <linux/seq_file.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
@@ -210,10 +211,10 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
 	DECLARE_BITMAP(vals, GPIOHANDLES_MAX);
 	unsigned int i;
 	int ret;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&lh->gdev->srcu);
-
-	if (!rcu_access_pointer(lh->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(lh->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	switch (cmd) {
@@ -1432,10 +1433,10 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
 {
 	struct linereq *lr = file->private_data;
 	void __user *ip = (void __user *)arg;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&lr->gdev->srcu);
-
-	if (!rcu_access_pointer(lr->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(lr->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	switch (cmd) {
@@ -1463,10 +1464,10 @@ static __poll_t linereq_poll(struct file *file,
 {
 	struct linereq *lr = file->private_data;
 	__poll_t events = 0;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&lr->gdev->srcu);
-
-	if (!rcu_access_pointer(lr->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(lr->gdev->chip_rp, gc);
+	if (!gc)
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &lr->wait, wait);
@@ -1485,10 +1486,10 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
 	struct gpio_v2_line_event le;
 	ssize_t bytes_read = 0;
 	int ret;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&lr->gdev->srcu);
-
-	if (!rcu_access_pointer(lr->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(lr->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	if (count < sizeof(le))
@@ -1781,10 +1782,10 @@ static __poll_t lineevent_poll(struct file *file,
 {
 	struct lineevent_state *le = file->private_data;
 	__poll_t events = 0;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->gdev->chip_rp, gc);
+	if (!gc)
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &le->wait, wait);
@@ -1819,10 +1820,10 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
 	ssize_t bytes_read = 0;
 	ssize_t ge_size;
 	int ret;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	/*
@@ -1901,10 +1902,10 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
 	struct lineevent_state *le = file->private_data;
 	void __user *ip = (void __user *)arg;
 	struct gpiohandle_data ghd;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	/*
@@ -2434,11 +2435,11 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	struct gpio_chardev_data *cdev = file->private_data;
 	struct gpio_device *gdev = cdev->gdev;
 	void __user *ip = (void __user *)arg;
-
-	guard(srcu)(&gdev->srcu);
+	struct gpio_chip *gc;
 
 	/* We fail any subsequent ioctl():s when the chip is gone */
-	if (!rcu_access_pointer(gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 	/* Fill in the struct and pass to userspace */
@@ -2497,12 +2498,9 @@ static void lineinfo_changed_func(struct work_struct *work)
 		 * Pin functions are in general much more static and while it's
 		 * not 100% bullet-proof, it's good enough for most cases.
 		 */
-		scoped_guard(srcu, &ctx->gdev->srcu) {
-			gc = srcu_dereference(ctx->gdev->chip, &ctx->gdev->srcu);
-			if (gc &&
-			    !pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset))
-				ctx->chg.info.flags |= GPIO_V2_LINE_FLAG_USED;
-		}
+		REVOCABLE_TRY_ACCESS_WITH(ctx->gdev->chip_rp, gc);
+		if (gc && !pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset))
+			ctx->chg.info.flags |= GPIO_V2_LINE_FLAG_USED;
 	}
 
 	ret = kfifo_in_spinlocked(&ctx->cdev->events, &ctx->chg, 1,
@@ -2583,10 +2581,10 @@ static __poll_t lineinfo_watch_poll(struct file *file,
 {
 	struct gpio_chardev_data *cdev = file->private_data;
 	__poll_t events = 0;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&cdev->gdev->srcu);
-
-	if (!rcu_access_pointer(cdev->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(cdev->gdev->chip_rp, gc);
+	if (!gc)
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &cdev->wait, pollt);
@@ -2606,10 +2604,10 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
 	ssize_t bytes_read = 0;
 	int ret;
 	size_t event_size;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&cdev->gdev->srcu);
-
-	if (!rcu_access_pointer(cdev->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(cdev->gdev->chip_rp, gc);
+	if (!gc)
 		return -ENODEV;
 
 #ifndef CONFIG_GPIO_CDEV_V1
-- 
2.53.0.rc2.204.g2597b5adb4-goog