gpio: provide gpiod_is_shared()

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>
Link: https://lore.kernel.org/r/20251112-gpio-shared-v4-6-b51f97b1abd8@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
index 1fcbf53b6eca4600c91706687fec462cb755dd12..fa1d16635ea7814d02725c3aa6185afc47c7423b 100644 (file)
--- 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 1e4c991797126d0d91233bbe7c3ae3831bf77d6c..678d07dc768c15de0235716e014e87dc2a7beaeb 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3990,6 +3990,26 @@ 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 09ac92ed0853f2ff0013d1b16a5dd082c9fd162e..abd870fb4a3be85c2efc59a55e78225e451aad84 100644 (file)
--- 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 (file)
--- 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;