driver core: Add support for linking devices during device addition

The firmware corresponding to a device (dev.fwnode) might be able to
provide functional dependency information between a device and its
supplier and consumer devices.  Tracking this functional dependency
allows optimizing device probe order and informing a supplier when all
its consumers have probed (and thereby actively managing their
resources).

The existing device links feature allows tracking and using
supplier-consumer relationships. So, this patch adds the add_links()
fwnode callback to allow firmware to create device links for each
device as the device is added.

However, when consumer devices are added, they might not have a supplier
device to link to despite needing mandatory resources/functionality from
one or more suppliers. A waiting_for_suppliers list is created to track
such consumers and retry linking them when new devices get added.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20190904211126.47518-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index d8c6d231d577..6ae05b9ce359 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -66,6 +66,21 @@ struct fwnode_reference_args {
  *			       endpoint node.
  * @graph_get_port_parent: Return the parent node of a port node.
  * @graph_parse_endpoint: Parse endpoint for port and endpoint id.
+ * @add_links:	Called after the device corresponding to the fwnode is added
+ *		using device_add(). The function is expected to create device
+ *		links to all the suppliers of the device that are available at
+ *		the time this function is called.  The function must NOT stop
+ *		at the first failed device link if other unlinked supplier
+ *		devices are present in the system.  If some suppliers are not
+ *		yet available, this function will be called again when other
+ *		devices are added to allow creating device links to any newly
+ *		available suppliers.
+ *
+ *		Return 0 if device links have been successfully created to all
+ *		the suppliers of this device or if the supplier information is
+ *		not known. Return an error if and only if the supplier
+ *		information is known but some of the suppliers are not yet
+ *		available to create device links to.
  */
 struct fwnode_operations {
 	struct fwnode_handle *(*get)(struct fwnode_handle *fwnode);
@@ -103,6 +118,8 @@ struct fwnode_operations {
 	(*graph_get_port_parent)(struct fwnode_handle *fwnode);
 	int (*graph_parse_endpoint)(const struct fwnode_handle *fwnode,
 				    struct fwnode_endpoint *endpoint);
+	int (*add_links)(const struct fwnode_handle *fwnode,
+			 struct device *dev);
 };
 
 #define fwnode_has_op(fwnode, op)				\