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.

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 d2087d0df4ab7bcd23d3736e341c0f57cd748af4..b5c33bccff0765eb940fedd5d678c47a05f1a25d 100644
--- a/drivers/gpio/gpiolib-shared.c
+++ b/drivers/gpio/gpiolib-shared.c
@@ -309,6 +309,24 @@ 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 03fd60e787fcf5846519fb2db9a701770ed15d6b..d689065471a1269ac0671b964c67670df5c95dd7 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3984,6 +3984,26 @@ 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 ae9aa145ca055c08dad55a537567a27de57f7066..8deed8a7d1128f01f0696af040d06f5fe140c7f8 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 00df68c514051434e6fa67dc2307c6a8ce4ce3df..a8acb7c0b5af5066fd05e533468fc28616c68d78 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);
@@ -520,6 +522,13 @@ 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;

-- 
2.48.1

On Wed, Oct 22, 2025 at 3:11 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> 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.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

On Tue, Nov 11, 2025 at 11:44 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Wed, Oct 22, 2025 at 3:11 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> > 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.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
>

I think you wanted to leave this under v3?

Bart

On Wed, Nov 12, 2025 at 9:06 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> On Tue, Nov 11, 2025 at 11:44 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> > On Wed, Oct 22, 2025 at 3:11 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >
> > > 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.
> > >
> > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> >
> > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> >
>
> I think you wanted to leave this under v3?

Yeah probably, a bit messy in my inbox!

Yours,
Linus Walleij