gpio: Support for unified device properties interface

Some drivers need to deal with only firmware representation of its
GPIOs. An example would be a GPIO button array driver where each button
is described as a separate firmware node in device tree. Typically these
child nodes do not have physical representation in the Linux device
model.

In order to help device drivers to handle such firmware child nodes we
add dev[m]_get_named_gpiod_from_child() that takes a child firmware
node pointer as its second argument (the first one is the parent device
itself), finds the GPIO using whatever is the underlying firmware
method, and requests the GPIO properly.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/drivers/gpio/devres.c b/drivers/gpio/devres.c
index 954b9f6b0ef8..13dbd3dfc33a 100644
--- a/drivers/gpio/devres.c
+++ b/drivers/gpio/devres.c
@@ -109,6 +109,38 @@ struct gpio_desc *__must_check __devm_gpiod_get_index(struct device *dev,
 EXPORT_SYMBOL(__devm_gpiod_get_index);
 
 /**
+ * devm_get_gpiod_from_child - get a GPIO descriptor from a device's child node
+ * @dev:        GPIO consumer
+ * @child:      firmware node (child of @dev)
+ *
+ * GPIO descriptors returned from this function are automatically disposed on
+ * driver detach.
+ */
+struct gpio_desc *devm_get_gpiod_from_child(struct device *dev,
+                                            struct fwnode_handle *child)
+{
+        struct gpio_desc **dr;
+        struct gpio_desc *desc;
+
+        dr = devres_alloc(devm_gpiod_release, sizeof(struct gpio_desc *),
+                          GFP_KERNEL);
+        if (!dr)
+                return ERR_PTR(-ENOMEM);
+
+        desc = fwnode_get_named_gpiod(child, "gpios");
+        if (IS_ERR(desc)) {
+                devres_free(dr);
+                return desc;
+        }
+
+        *dr = desc;
+        devres_add(dev, dr);
+
+        return desc;
+}
+EXPORT_SYMBOL(devm_get_gpiod_from_child);
+
+/**
  * devm_gpiod_get_index_optional - Resource-managed gpiod_get_index_optional()
  * @dev: GPIO consumer
  * @con_id: function within the GPIO consumer