[PATCH 1/2] gpio: core: fix const-correctness of gpio_chip_guard

[Marco Scardovi (scardracs)]

The DEFINE_CLASS macro for gpio_chip_guard currently expects a non-const
struct gpio_desc pointer. This prevents the guard from being used cleanly
in fast paths that receive a const descriptor, forcing developers to fall
back to open-coding the SRCU locks.

Update the macro to accept a const struct gpio_desc pointer. This is valid
because the actual targeted gpio_device pointer assignment does not drop
const qualifiers on the target structure.

Convert the open-coded SRCU locks in gpiod_get_raw_value_commit() and
gpiod_to_irq() to use the guard, removing their legacy FIXME comments.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Marco Scardovi <scardracs@xxxxxxxxxxx>
---
 drivers/gpio/gpiolib.c | 28 ++++++++--------------------
 drivers/gpio/gpiolib.h |  2 +-
 2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 69743d6deeaf..6b0c6e8abf7b 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3428,20 +3428,13 @@ 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);
-	if (!gc)
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
 		return -ENODEV;
 
-	value = gpio_chip_get_value(gc, desc);
+	value = gpio_chip_get_value(guard.gc, desc);
 	value = value < 0 ? value : !!value;
 	trace_gpio_value(desc_to_gpio(desc), 1, value);
 	return value;
@@ -4148,8 +4141,6 @@ 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;
 
@@ -4157,16 +4148,13 @@ 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);
-	if (!gc)
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
 		return -ENODEV;
 
 	offset = gpiod_hwgpio(desc);
-	if (gc->to_irq) {
-		ret = gc->to_irq(gc, offset);
+	if (guard.gc->to_irq) {
+		ret = guard.gc->to_irq(guard.gc, offset);
 		if (ret)
 			return ret;
 
@@ -4174,7 +4162,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 		return -ENXIO;
 	}
 #ifdef CONFIG_GPIOLIB_IRQCHIP
-	if (gc->irq.chip) {
+	if (guard.gc->irq.chip) {
 		/*
 		 * Avoid race condition with other code, which tries to lookup
 		 * an IRQ before the irqchip has been properly registered,
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index dc4cb61a9318..650a702741df 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -244,7 +244,7 @@ DEFINE_CLASS(gpio_chip_guard,
 
 		_guard;
 	     }),
-	     struct gpio_desc *desc)
+	     const struct gpio_desc *desc)
 
 int gpiod_request(struct gpio_desc *desc, const char *label);
 int gpiod_request_commit(struct gpio_desc *desc, const char *label);
-- 
2.54.0