[PATCH v4 06/10] gpio: provide gpiod_is_shared()

Bartosz Golaszewski
2025-11-12T13:55:50Z

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Provide an interface allowing consumers to check if a GPIO descriptor
represents a GPIO that can potentially be shared by multiple consumers
at the same time. This is exposed to allow subsystems that already
work around the limitations of the current non-exclusive GPIO handling
in some ways, to gradually convert to relying on the new shared GPIO
feature of GPIOLIB.

Extend the gpiolib-shared module to mark the GPIO shared proxy
descriptors with a flag checked by the new interface.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
drivers/gpio/gpiolib-shared.c | 18 ++++++++++++++++++
drivers/gpio/gpiolib.c | 20 ++++++++++++++++++++
drivers/gpio/gpiolib.h | 1 +
include/linux/gpio/consumer.h | 9 +++++++++
4 files changed, 48 insertions(+)

diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
index 56b9b03cbb6dbcdf095a656fc36ff321770035da..c22eaf05eef23a7f5f111708c3db9412c4c30231 100644
--- a/drivers/gpio/gpiolib-shared.c
+++ b/drivers/gpio/gpiolib-shared.c
@@ -314,6 +314,24 @@ int gpio_device_setup_shared(struct gpio_device *gdev)

guard(mutex)(&gpio_shared_lock);

+ list_for_each_entry(entry, &gpio_shared_list, list) {
+ list_for_each_entry(ref, &entry->refs, list) {
+ if (gdev->dev.parent == &ref->adev.dev) {
+ /*
+ * This is a shared GPIO proxy. Mark its
+ * descriptor as such and return here.
+ */
+ __set_bit(GPIOD_FLAG_SHARED_PROXY,
+ &gdev->descs[0].flags);
+ return 0;
+ }
+ }
+ }
+
+ /*
+ * This is not a shared GPIO proxy but it still may be the device
+ * exposing shared pins. Find them and create the proxy devices.
+ */
list_for_each_entry(entry, &gpio_shared_list, list) {
if (!device_match_fwnode(&gdev->dev, entry->fwnode))
continue;
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index c59fe05c838e073b4bc99c4a7667cb1ff40c26b4..91e0c384f34ae5c0ed61ccd3a978685d4f72e867 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3997,6 +3997,26 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
}
EXPORT_SYMBOL_GPL(gpiod_set_consumer_name);

+/**
+ * gpiod_is_shared() - check if this GPIO can be shared by multiple consumers
+ * @desc: GPIO to inspect
+ *
+ * Returns:
+ * True if this GPIO can be shared by multiple consumers at once. False if it's
+ * a regular, exclusive GPIO.
+ *
+ * Note:
+ * This function returning true does not mean that this GPIO is currently being
+ * shared. It means the GPIO core has registered the fact that the firmware
+ * configuration indicates that it can be shared by multiple consumers and is
+ * in charge of arbitrating the access.
+ */
+bool gpiod_is_shared(const struct gpio_desc *desc)
+{
+ return test_bit(GPIOD_FLAG_SHARED_PROXY, &desc->flags);
+}
+EXPORT_SYMBOL_GPL(gpiod_is_shared);
+
/**
* gpiod_to_irq() - return the IRQ corresponding to a GPIO
* @desc: gpio whose IRQ will be returned (already requested)
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index c9de4bb10584206f4888c0f28468762a3680aae6..77f6f2936dc263a67b31a38799a841128a57603a 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -205,6 +205,7 @@ struct gpio_desc {
#define GPIOD_FLAG_EVENT_CLOCK_REALTIME 18 /* GPIO CDEV reports REALTIME timestamps in events */
#define GPIOD_FLAG_EVENT_CLOCK_HTE 19 /* GPIO CDEV reports hardware timestamps in events */
#define GPIOD_FLAG_SHARED 20 /* GPIO is shared by multiple consumers */
+#define GPIOD_FLAG_SHARED_PROXY 21 /* GPIO is a virtual proxy to a physically shared pin. */

/* Connection label */
struct gpio_desc_label __rcu *label;
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index 994d46874d560416175c9099e18180237839bd4c..cafeb7a40ad1c25aeb7deaf598410d5f2f004a82 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -167,6 +167,8 @@ int gpiod_cansleep(const struct gpio_desc *desc);
int gpiod_to_irq(const struct gpio_desc *desc);
int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name);

+bool gpiod_is_shared(const struct gpio_desc *desc);
+
/* Convert between the old gpio_ and new gpiod_ interfaces */
struct gpio_desc *gpio_to_desc(unsigned gpio);
int desc_to_gpio(const struct gpio_desc *desc);
@@ -522,6 +524,13 @@ static inline int gpiod_set_consumer_name(struct gpio_desc *desc,
return -EINVAL;
}

+static inline bool gpiod_is_shared(const struct gpio_desc *desc)
+{
+ /* GPIO can never have been requested */
+ WARN_ON(desc);
+ return false;
+}
+
static inline struct gpio_desc *gpio_to_desc(unsigned gpio)
{
return NULL;

--
2.51.0