[PATCH v9 1/5] driver core: Find an existing link between two devices

[Vivek Gautam]

The lists managing the device-links can be traversed to
find the link between two devices. The device_link_add() APIs
does traverse these lists to check if there's already a link
setup between the two devices.
So, add a new APIs, device_link_find(), to find an existing
device link between two devices - suppliers and consumers.

Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---

 * New patch added to this series.

 drivers/base/core.c    | 30 +++++++++++++++++++++++++++---
 include/linux/device.h |  2 ++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5847364f25d9..e8c9774e4ba2 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -144,6 +144,30 @@ static int device_reorder_to_tail(struct device *dev, void *not_used)
 	return 0;
 }
 
+/**
+ * device_link_find - find any existing link between two devices.
+ * @consumer: Consumer end of the link.
+ * @supplier: Supplier end of the link.
+ *
+ * Returns pointer to the existing link between a supplier and
+ * and consumer devices, or NULL if no link exists.
+ */
+struct device_link *device_link_find(struct device *consumer,
+				     struct device *supplier)
+{
+	struct device_link *link = NULL;
+
+	if (!consumer || !supplier)
+		return NULL;
+
+	list_for_each_entry(link, &supplier->links.consumers, s_node)
+		if (link->consumer == consumer)
+			break;
+
+	return link;
+}
+EXPORT_SYMBOL_GPL(device_link_find);
+
 /**
  * device_link_add - Create a link between two devices.
  * @consumer: Consumer end of the link.
@@ -195,9 +219,9 @@ struct device_link *device_link_add(struct device *consumer,
 		goto out;
 	}
 
-	list_for_each_entry(link, &supplier->links.consumers, s_node)
-		if (link->consumer == consumer)
-			goto out;
+	link = device_link_find(consumer, supplier);
+	if (link)
+		goto out;
 
 	link = kzalloc(sizeof(*link), GFP_KERNEL);
 	if (!link)
diff --git a/include/linux/device.h b/include/linux/device.h
index b093405ed525..13bc1884c3eb 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1278,6 +1278,8 @@ extern const char *dev_driver_string(const struct device *dev);
 struct device_link *device_link_add(struct device *consumer,
 				    struct device *supplier, u32 flags);
 void device_link_del(struct device_link *link);
+struct device_link *device_link_find(struct device *consumer,
+				     struct device *supplier);
 
 #ifdef CONFIG_PRINTK
 
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