rpmsg: char: Add possibility to use default endpoint of the rpmsg device

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 a default endpoint is created.
In this case we have to reuse the default rpmsg device endpoint associated to
the channel instead of creating a new one.

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 default_ept field in rpmsg_eptdev structure.This pointer
determines the behavior on rpmsg_eptdev_open and rpmsg_eptdev_release call.

- If default_ept == NULL:
  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 default_ept is set:
  use the rpmsg device default endpoint for the communication.

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

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220124102524.295783-10-arnaud.pouliquen@foss.st.com

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index bf7311d64e429d49b68f7d26018bf2239ceed0ee..8430d568fdd0a8c8f37ac9828d0c20ccd51218ec 100644 (file)
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -50,6 +50,8 @@ static DEFINE_IDA(rpmsg_minor_ida);
  * @queue_lock:        synchronization of @queue operations
  * @queue:     incoming message queue
  * @readq:     wait object for incoming queue
+ * @default_ept: set to channel default endpoint if the default endpoint should be re-used
+ *              on device open to prevent endpoint address update.
  */
 struct rpmsg_eptdev {
        struct device dev;
@@ -60,10 +62,12 @@ struct rpmsg_eptdev {
 
        struct mutex ept_lock;
        struct rpmsg_endpoint *ept;
+       struct rpmsg_endpoint *default_ept;
 
        spinlock_t queue_lock;
        struct sk_buff_head queue;
        wait_queue_head_t readq;
+
 };
 
 int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
@@ -121,7 +125,15 @@ 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 default_ept is set, the rpmsg device default endpoint is used.
+        * Else a new endpoint is created on open that will be destroyed on release.
+        */
+       if (eptdev->default_ept)
+               ept = eptdev->default_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);
@@ -142,7 +154,8 @@ 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->default_ept)
+                       rpmsg_destroy_ept(eptdev->ept);
                eptdev->ept = NULL;
        }
        mutex_unlock(&eptdev->ept_lock);
@@ -272,6 +285,10 @@ 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->default_ept)
+               return -EINVAL;
+
        return rpmsg_chrdev_eptdev_destroy(&eptdev->dev, NULL);
 }