[PATCH v3 4/6] rpmsg: char: Add possibility to create and reuse default endpoint

[Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>]

This patch prepares the introduction of a rpmsg channel device for the
char device. The rpmsg channel device will require a default endpoint to
communicate to the remote processor.

Add the use_default_ept field in rpmsg_eptdev structure. This boolean
determines the behavior on rpmsg_eptdev_open and rpmsg_eptdev_release call.

- If use_default_ept == false:
  Use the legacy behavior by creating a new endpoint each time
  rpmsg_eptdev_open is called and release it when rpmsg_eptdev_release
  is called on /dev/rpmsgX device open/close.

- if use_default_ept == true:
  create a endpoint only on first rpmsg_eptdev_open call (if no default
  endpoint already exists) and associate it to the default endpoint.
  The endpoint is released when the rpmsg device is removed.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

---
Update from V2

This patch is a merge of two patches proposed in V2
 rpmsg: char: Introduce __rpmsg_chrdev_create_eptdev function
 rpmsg: char: No dynamic endpoint management for the default one

With the introduction of the use_default_ept to determine the behaviour
on  rpmsg_eptdev_open/release.
---
 drivers/rpmsg/rpmsg_char.c | 46 +++++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 3b07a050b75e..5c6a7da6e4d7 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -38,6 +38,8 @@ static DEFINE_IDA(rpmsg_minor_ida);
  * @queue_lock:	synchronization of @queue operations
  * @queue:	incoming message queue
  * @readq:	wait object for incoming queue
+ * @use_default_ept: specify if the endpoint has to be created at each device opening or
+ *                   if the default endpoint should be reused.
  */
 struct rpmsg_eptdev {
 	struct device dev;
@@ -52,6 +54,8 @@ struct rpmsg_eptdev {
 	spinlock_t queue_lock;
 	struct sk_buff_head queue;
 	wait_queue_head_t readq;
+
+	bool use_default_ept;
 };
 
 int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
@@ -109,11 +113,29 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
 
 	get_device(dev);
 
-	ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
-	if (!ept) {
-		dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
-		put_device(dev);
-		return -EINVAL;
+	/*
+	 * If the rpmsg device default endpoint is used, create it only the first time then reuse
+	 * it. Else a new endpoint is created on open that will be destroyed on release.
+	 */
+	if (eptdev->use_default_ept && rpdev->ept) {
+		ept = rpdev->ept;
+	} else {
+		ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
+		if (!ept) {
+			dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
+			put_device(dev);
+			return -EINVAL;
+		}
+
+		if (eptdev->use_default_ept) {
+			/*
+			 * Assign the new endpoint as default endpoint and update the channel
+			 * info source to reflect the allocation in the rpmsg class.
+			 */
+			rpdev->ept = ept;
+			rpdev->src = ept->addr;
+			eptdev->chinfo.src = rpdev->src;
+		}
 	}
 
 	eptdev->ept = ept;
@@ -130,7 +152,8 @@ static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
 	/* Close the endpoint, if it's not already destroyed by the parent */
 	mutex_lock(&eptdev->ept_lock);
 	if (eptdev->ept) {
-		rpmsg_destroy_ept(eptdev->ept);
+		if (!eptdev->use_default_ept)
+			rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
 	}
 	mutex_unlock(&eptdev->ept_lock);
@@ -316,8 +339,8 @@ static void rpmsg_eptdev_release_device(struct device *dev)
 	kfree(eptdev);
 }
 
-int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
-			       struct rpmsg_channel_info chinfo)
+static int __rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
+					struct rpmsg_channel_info chinfo, bool use_default_ept)
 {
 	struct rpmsg_eptdev *eptdev;
 	struct device *dev;
@@ -330,6 +353,7 @@ int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent
 	dev = &eptdev->dev;
 	eptdev->rpdev = rpdev;
 	eptdev->chinfo = chinfo;
+	eptdev->use_default_ept = use_default_ept;
 
 	mutex_init(&eptdev->ept_lock);
 	spin_lock_init(&eptdev->queue_lock);
@@ -381,6 +405,12 @@ int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent
 
 	return ret;
 }
+
+int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
+			       struct rpmsg_channel_info chinfo)
+{
+	return __rpmsg_chrdev_eptdev_create(rpdev, parent, chinfo, false);
+}
 EXPORT_SYMBOL(rpmsg_chrdev_eptdev_create);
 
 static int rpmsg_chrdev_init(void)
-- 
2.17.1