drivers/of: Add the of_find_i2c_device_by_node function.

The of_find_i2c_device_by_node function allows you to follow a
reference in the device tree to an i2c device node and then locate
the linux device instantiated by the device tree. Example use: an I2S
bus driver finding the i2c_device instance for a codec described by
a device tree node.

This was waiting for Anton's i2c patches that were just added.
Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/of/of_i2c.c

@@ -66,4 +66,23 @@ void of_register_i2c_devices(struct i2c_adapter *adap,
 }
 EXPORT_SYMBOL(of_register_i2c_devices);
 
+static int of_dev_node_match(struct device *dev, void *data)
+{
+        return dev_archdata_get_node(&dev->archdata) == data;
+}
+
+/* must call put_device() when done with returned i2c_client device */
+struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
+{
+	struct device *dev;
+
+	dev = bus_find_device(&i2c_bus_type, NULL, node,
+					 of_dev_node_match);
+	if (!dev)
+		return NULL;
+
+	return to_i2c_client(dev);
+}
+EXPORT_SYMBOL(of_find_i2c_device_by_node);
+
 MODULE_LICENSE("GPL");

include/linux/of_i2c.h

@@ -17,4 +17,7 @@
 void of_register_i2c_devices(struct i2c_adapter *adap,
 			     struct device_node *adap_node);
 
+/* must call put_device() when done with returned i2c_client device */
+struct i2c_client *of_find_i2c_device_by_node(struct device_node *node);
+
 #endif /* __LINUX_OF_I2C_H */