[PATCH v2 3/4] rpmsg: char: Add possibility to use default endpoint of the rpmsg device.

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

Current implementation create/destroy a new endpoint on each
rpmsg_eptdev_open/rpmsg_eptdev_release calls.

For a rpmsg device created by the NS announcement mechanism we need to
use a unique static endpoint that is the default rpmsg device endpoint
associated to the channel.

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

- If static_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 static_ept == true:
  use the rpmsg device default endpoint for the communication.
- Address the update of _rpmsg_chrdev_eptdev_create in e separate patch for readability.

Add protection in rpmsg_eptdev_ioctl to prevent to destroy a default endpoint.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
---
update vs V1:
- remove the management of the default endpoint creation from rpmsg_eptdev_open.

---
 drivers/rpmsg/rpmsg_char.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 50b7d4b00175..a75dce1e29d8 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -45,6 +45,8 @@ static DEFINE_IDA(rpmsg_minor_ida);
  * @queue_lock:	synchronization of @queue operations
  * @queue:	incoming message queue
  * @readq:	wait object for incoming queue
+ * @static_ept: specify if the endpoint has to be created at each device opening or
+ *              if the default endpoint should be used.
  */
 struct rpmsg_eptdev {
 	struct device dev;
@@ -59,6 +61,8 @@ struct rpmsg_eptdev {
 	spinlock_t queue_lock;
 	struct sk_buff_head queue;
 	wait_queue_head_t readq;
+
+	bool static_ept;
 };
 
 int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
@@ -116,7 +120,15 @@ 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 the static_ept is set to true, the rpmsg device default endpoint is used.
+	 * Else a new endpoint is created on open that will be destroyed on release.
+	 */
+	if (eptdev->static_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);
@@ -137,7 +149,8 @@ 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->static_ept)
+			rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
 	}
 	mutex_unlock(&eptdev->ept_lock);
@@ -264,6 +277,10 @@ static long rpmsg_eptdev_ioctl(struct file *fp, unsigned int cmd,
 	if (cmd != RPMSG_DESTROY_EPT_IOCTL)
 		return -EINVAL;
 
+	/* Don't allow to destroy a default endpoint. */
+	if (!eptdev->rpdev || eptdev->ept == eptdev->rpdev->ept)
+		return -EPERM;
+
 	return rpmsg_chrdev_eptdev_destroy(&eptdev->dev, NULL);
 }
 
-- 
2.17.1