[PATCH v7 02/16] device property: Add fwnode_graph_get_next_port_endpoint()

Due to design constraints of the power sequencing API, the consumer
must first be sure that the other side is actually a provider, or it
will continually get -EPROBE_DEFER when requesting the power
sequencing descriptor.

In the upcoming USB power sequencing integration, the USB hub driver
first needs to check whether a graph connection exists, and whether
the other side of the connection is a supported connector type. The
USB port is tied to a "port" firmware node, and this new helper will
be used to get the endpoint under the known "port" firmware node.

Sashiko points out that the |prev| reference put is not done if |port|
is NULL. However it seems that the fwnode_*() and of_*() API design
implicitly makes the functions no-ops if the passed in node is NULL.
So this new addition follows the same pattern.

Cc: Sakari Ailus <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Bartosz Golaszewski <[email protected]>
Signed-off-by: Chen-Yu Tsai <[email protected]>
---
Changes since v2:
- Dropped unused |ep| variable
- Rewrote as do {} while()
- Dropped WARN() use
---
 drivers/base/property.c  | 25 +++++++++++++++++++++++++
 include/linux/property.h |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/drivers/base/property.c b/drivers/base/property.c
index 950defc0c55a..5d3993bd8fc4 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -1099,6 +1099,31 @@ int fwnode_irq_get_byname(const struct fwnode_handle *fwnode, const char *name)
 }
 EXPORT_SYMBOL(fwnode_irq_get_byname);
 
+/**
+ * fwnode_graph_get_next_port_endpoint - Get next endpoint firmware node in port
+ * @port: Pointer to the target port firmware node
+ * @prev: Previous endpoint node or %NULL to get the first
+ *
+ * The caller is responsible for calling fwnode_handle_put() on the returned
+ * fwnode pointer. Note that this function also puts a reference to @prev
+ * unconditionally.
+ *
+ * Return: an endpoint firmware node pointer or %NULL if no more endpoints
+ * are available.
+ */
+struct fwnode_handle *fwnode_graph_get_next_port_endpoint(const struct fwnode_handle *port,
+							  struct fwnode_handle *prev)
+{
+	do {
+		prev = fwnode_get_next_child_node(port, prev);
+		if (fwnode_name_eq(prev, "endpoint"))
+			break;
+	} while (prev);
+
+	return prev;
+}
+EXPORT_SYMBOL_GPL(fwnode_graph_get_next_port_endpoint);
+
 /**
  * fwnode_graph_get_next_endpoint - Get next endpoint firmware node
  * @fwnode: Pointer to the parent firmware node
diff --git a/include/linux/property.h b/include/linux/property.h
index 01ea010cb2f9..9a784a856773 100644
--- a/include/linux/property.h
+++ b/include/linux/property.h
@@ -507,6 +507,8 @@ void __iomem *fwnode_iomap(struct fwnode_handle *fwnode, int index);
 
 struct fwnode_handle *fwnode_graph_get_port_by_id(struct fwnode_handle *fwnode, u32 id,
 						  unsigned long flags);
+struct fwnode_handle *fwnode_graph_get_next_port_endpoint(
+	const struct fwnode_handle *port, struct fwnode_handle *prev);
 struct fwnode_handle *fwnode_graph_get_next_endpoint(
 	const struct fwnode_handle *fwnode, struct fwnode_handle *prev);
 struct fwnode_handle *
-- 
2.55.0.229.g6434b31f56-goog