[PATCH v2] rpmsg: virtio: set dst address on first message received

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

When a rpmsg channel has been created locally with a destination address
set to RPMSG_ADDR_ANY, a name service announcement message is sent to
the remote side. Then the destination address is never updated, making it
impossible to send messages to the remote.

An example of kernel trace observed:
rpmsg_tty virtio0.rpmsg-tty.29.-1: invalid addr (src 0x1d, dst 0xffffffff)

Implement same strategy than the open-amp library:
On the reception of the first message, if the destination address is
RPMSG_ADDR_ANY, then set it to address of the remote endpoint that
send the message.

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

---
Update from V1:
- fix rpmsg address conversion from fvirtio to cpu format,
  reported-by the kernel test robot <lkp@intel.com>.

Remarks:

- This issue has been detected during validation of the rpmsg_char
  restructuring series on going[1].
  Tested on the rpmsg_next branch[2]

- An alternative (or a complement?) could be to add a NS bind/unbind in
  the NS announcement channel (in rpmsg_ns.c).
  This would allow the local and/or the remote processor to inform the
  remote side the the service announced in bound.

[1] https://lkml.org/lkml/2022/1/24/293
[2] https://git.kernel.org/pub/scm/linux/kernel/git/remoteproc/linux.git/log/?h=for-next

---
 drivers/rpmsg/virtio_rpmsg_bus.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
index 3ede25b1f2e4..152b54b83782 100644
--- a/drivers/rpmsg/virtio_rpmsg_bus.c
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -708,6 +708,7 @@ static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept)
 static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
 			     struct rpmsg_hdr *msg, unsigned int len)
 {
+	struct rpmsg_device *rpdev;
 	struct rpmsg_endpoint *ept;
 	struct scatterlist sg;
 	bool little_endian = virtio_is_little_endian(vrp->vdev);
@@ -746,6 +747,15 @@ static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
 	mutex_unlock(&vrp->endpoints_lock);
 
 	if (ept) {
+		rpdev = ept->rpdev;
+		if (rpdev->ept == ept && rpdev->dst == RPMSG_ADDR_ANY) {
+			/*
+			 * First message received from the remote side on the default endpoint,
+			 * update channel destination address.
+			 */
+			rpdev->dst = __rpmsg32_to_cpu(little_endian, msg->src);
+		}
+
 		/* make sure ept->cb doesn't go away while we use it */
 		mutex_lock(&ept->cb_lock);
 
-- 
2.25.1