rpmsg: Support drivers without primary endpoint

Some types of rpmsg drivers does not have a primary endpoint to tie
their existence upon, but wishes to create and destroy endpoints
dynamically, e.g. based on user interactions.

Allow rpmsg drivers to omit a driver callback to signal this case and
make the probe path not create a primary endpoint in this case.
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/rpmsg_core.c

@@ -347,9 +347,10 @@ static int rpmsg_dev_probe(struct device *dev)
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
 	struct rpmsg_driver *rpdrv = to_rpmsg_driver(rpdev->dev.driver);
 	struct rpmsg_channel_info chinfo = {};
-	struct rpmsg_endpoint *ept;
+	struct rpmsg_endpoint *ept = NULL;
 	int err;
 
+	if (rpdrv->callback) {
 		strncpy(chinfo.name, rpdev->id.name, RPMSG_NAME_SIZE);
 		chinfo.src = rpdev->src;
 		chinfo.dst = RPMSG_ADDR_ANY;
@@ -363,10 +364,12 @@ static int rpmsg_dev_probe(struct device *dev)
 
 		rpdev->ept = ept;
 		rpdev->src = ept->addr;
+	}
 
 	err = rpdrv->probe(rpdev);
 	if (err) {
 		dev_err(dev, "%s: failed: %d\n", __func__, err);
+		if (ept)
 			rpmsg_destroy_ept(ept);
 		goto out;
 	}
@@ -388,6 +391,7 @@ static int rpmsg_dev_remove(struct device *dev)
 
 	rpdrv->remove(rpdev);
 
+	if (rpdev->ept)
 		rpmsg_destroy_ept(rpdev->ept);
 
 	return err;