driver core: Add fwnode_to_dev() to look up device from fwnode

It's often useful to look up a device that corresponds to a fwnode. So
add an API to do that irrespective of the bus on which the device has
been added to.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20190904211126.47518-2-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -2198,6 +2198,10 @@ int device_add(struct device *dev)
 					     BUS_NOTIFY_ADD_DEVICE, dev);
 
 	kobject_uevent(&dev->kobj, KOBJ_ADD);
+
+	if (dev->fwnode && !dev->fwnode->dev)
+		dev->fwnode->dev = dev;
+
 	bus_probe_device(dev);
 	if (parent)
 		klist_add_tail(&dev->p->knode_parent,
@@ -2342,6 +2346,9 @@ void device_del(struct device *dev)
 	kill_device(dev);
 	device_unlock(dev);
 
+	if (dev->fwnode && dev->fwnode->dev == dev)
+		dev->fwnode->dev = NULL;
+
 	/* Notify clients of device removal.  This call must come
 	 * before dpm_sysfs_remove().
 	 */

include/linux/fwnode.h

@@ -17,6 +17,7 @@ struct device;
 struct fwnode_handle {
 	struct fwnode_handle *secondary;
 	const struct fwnode_operations *ops;
+	struct device *dev;
 };
 
 /**
@@ -123,5 +124,6 @@ struct fwnode_operations {
 		if (fwnode_has_op(fwnode, op))				\
 			(fwnode)->ops->op(fwnode, ## __VA_ARGS__);	\
 	} while (false)
+#define get_dev_from_fwnode(fwnode)	get_device((fwnode)->dev)
 
 #endif