modem: cmux: Add DLCI receive buffer overrun LOG WRN

DLCI receive buffer may overrun if data is not processed fast
enough. This error was not reported before this patch, resulting
in unexplained missing bytes.

Signed-off-by: Bjarki Arge Andreasen <[email protected]>

Author: bjarki-andreasen

subsys/modem/modem_cmux.c

@@ -546,15 +546,19 @@ static void modem_cmux_on_dlci_frame_ua(struct modem_cmux_dlci *dlci)
 static void modem_cmux_on_dlci_frame_uih(struct modem_cmux_dlci *dlci)
 {
 	struct modem_cmux *cmux = dlci->cmux;
+	uint32_t written;
 
 	if (dlci->state != MODEM_CMUX_DLCI_STATE_OPEN) {
 		LOG_DBG("Unexpected UIH frame");
 		return;
 	}
 
 	k_mutex_lock(&dlci->receive_rb_lock, K_FOREVER);
-	ring_buf_put(&dlci->receive_rb, cmux->frame.data, cmux->frame.data_len);
+	written = ring_buf_put(&dlci->receive_rb, cmux->frame.data, cmux->frame.data_len);
 	k_mutex_unlock(&dlci->receive_rb_lock);
+	if (written != cmux->frame.data_len) {
+		LOG_WRN("DLCI %u receive buffer overrun", dlci->dlci_address);
+	}
 	modem_pipe_notify_receive_ready(&dlci->pipe);
 }