[PATCH v6 5/5] samples: rpmsg: add MTU size info

[Tanmay Shah <tanmay.shah@amd.com>]

RPMsg MTU size can be variable now and no longer hardcoded to 512 bytes.
Add log to the sample driver that prints current MTU size of the rpmsg
buffer.

Changes in v4:
  - check msg size is < MTU size

Changes in v3:
  - Check for error when retrieving MTU size
  - %s/mtu/MTU/

Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
---
 samples/rpmsg/rpmsg_client_sample.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/samples/rpmsg/rpmsg_client_sample.c b/samples/rpmsg/rpmsg_client_sample.c
index ae5081662283..4c43436aadb6 100644
--- a/samples/rpmsg/rpmsg_client_sample.c
+++ b/samples/rpmsg/rpmsg_client_sample.c
@@ -52,6 +52,7 @@ static int rpmsg_sample_probe(struct rpmsg_device *rpdev)
 {
 	int ret;
 	struct instance_data *idata;
+	ssize_t mtu, msg_len;
 
 	dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x!\n",
 					rpdev->src, rpdev->dst);
@@ -62,8 +63,25 @@ static int rpmsg_sample_probe(struct rpmsg_device *rpdev)
 
 	dev_set_drvdata(&rpdev->dev, idata);
 
+	mtu = rpmsg_get_mtu(rpdev->ept);
+	if (mtu < 0) {
+		dev_warn(&rpdev->dev, "invalid rpmsg MTU size = %ld\n", mtu);
+		return mtu;
+	}
+
+	dev_info(&rpdev->dev, "rpmsg MTU size = %ld\n", mtu);
+
+	msg_len = strlen(MSG);
+	/* make sure our message fits in a single rpmsg buffer */
+	if (msg_len > mtu) {
+		dev_err(&rpdev->dev,
+			"message size %zu exceeds rpmsg MTU size %ld\n",
+			strlen(MSG), mtu);
+		return -EMSGSIZE;
+	}
+
 	/* send a message to our remote processor */
-	ret = rpmsg_send(rpdev->ept, MSG, strlen(MSG));
+	ret = rpmsg_send(rpdev->ept, MSG, msg_len);
 	if (ret) {
 		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
 		return ret;
-- 
2.43.0