[PATCH/RFC v2 2/6] base: devcon: add a new API to find the graph

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

This patch adds a new API "device_connection_find_by_graph()" to
find device connection by using graph.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
---
 Documentation/driver-api/device_connection.rst |  4 +--
 drivers/base/devcon.c                          | 43 ++++++++++++++++++++++++++
 include/linux/device.h                         |  2 ++
 3 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/Documentation/driver-api/device_connection.rst b/Documentation/driver-api/device_connection.rst
index affbc556..2e2d26f 100644
--- a/Documentation/driver-api/device_connection.rst
+++ b/Documentation/driver-api/device_connection.rst
@@ -19,7 +19,7 @@ Device connections alone do not create a dependency between the two devices.
 They are only descriptions which are not tied to either of the devices directly.
 A dependency between the two devices exists only if one of the two endpoint
 devices requests a reference to the other. The descriptions themselves can be
-defined in firmware (not yet supported) or they can be built-in.
+defined in firmware or they can be built-in.
 
 Usage
 -----
@@ -40,4 +40,4 @@ API
 ---
 
 .. kernel-doc:: drivers/base/devcon.c
-   : functions: device_connection_find_match device_connection_find device_connection_add device_connection_remove
+   : functions: device_connection_find_match device_connection_find device_connection_add device_connection_remove device_connection_find_by_graph
diff --git a/drivers/base/devcon.c b/drivers/base/devcon.c
index d427e80..5a0da33 100644
--- a/drivers/base/devcon.c
+++ b/drivers/base/devcon.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/device.h>
+#include <linux/property.h>
 
 static DEFINE_MUTEX(devcon_lock);
 static LIST_HEAD(devcon_list);
@@ -134,3 +135,45 @@ void device_connection_remove(struct device_connection *con)
 	mutex_unlock(&devcon_lock);
 }
 EXPORT_SYMBOL_GPL(device_connection_remove);
+
+static int generic_graph_match(struct device *dev, void *fwnode)
+{
+	return dev->fwnode == fwnode;
+}
+
+/**
+ * device_connection_find_by_graph - Find two devices connected together
+ * @dev: Device to find connected device
+ * @port: identifier of the @dev port node
+ * @endpoint: identifier of the @dev endpoint node
+ *
+ * Find a connection with @port and @endpoint by using graph between @dev and
+ * another device. On success returns handle to the device that is connected
+ * to @dev, with the reference count for the found device incremented. Returns
+ * NULL if no matching connection was found, or ERR_PTR(-EPROBE_DEFER) when
+ * a connection was found but the other device has not been enumerated yet.
+ */
+struct device *device_connection_find_by_graph(struct device *dev, u32 port,
+					       u32 endpoint)
+{
+	struct bus_type *bus;
+	struct fwnode_handle *remote;
+	struct device *conn;
+
+	remote = fwnode_graph_get_remote_node(dev_fwnode(dev), port, endpoint);
+	if (!remote)
+		return NULL;
+
+	for (bus = generic_match_buses[0]; bus; bus++) {
+		conn = bus_find_device(bus, NULL, remote, generic_graph_match);
+		if (conn)
+			return conn;
+	}
+
+	/*
+	 * We only get called if a connection was found, tell the caller to
+	 * wait for the other device to show up.
+	 */
+	return ERR_PTR(-EPROBE_DEFER);
+}
+EXPORT_SYMBOL_GPL(device_connection_find_by_graph);
diff --git a/include/linux/device.h b/include/linux/device.h
index 0059b99..58f8544 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -751,6 +751,8 @@ void *device_connection_find_match(struct device *dev, const char *con_id,
 
 void device_connection_add(struct device_connection *con);
 void device_connection_remove(struct device_connection *con);
+struct device *device_connection_find_by_graph(struct device *dev, u32 port,
+					       u32 endpoint);
 
 /**
  * enum device_link_state - Device link states.
-- 
1.9.1