ENGR00322581-03 tty: serial: imx: start rx_dma once RXFIFO is not empty

Start rx_dma once RXFIFO is not empty that can avoid dma request lost
and causes data delay issue.

Signed-off-by: Robin Gong <b38343@freescale.com>
Signed-off-by: Fugang Duan <B38611@freescale.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 81ee2f23d0a8..c73c05b33c49 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -936,8 +936,21 @@ static void dma_rx_callback(void *data)
                 tty_flip_buffer_push(port);
 
                 start_rx_dma(sport);
-        } else
+        } else if (readl(sport->port.membase + USR2) & USR2_RDR) {
+                /*
+                 * start rx_dma directly once data in RXFIFO, more efficient
+                 * than before:
+                 *      1. call imx_rx_dma_done to stop dma if no data received
+                 *      2. wait next  RDR interrupt to start dma transfer.
+                 */
+                start_rx_dma(sport);
+        } else {
+                /*
+                 * stop dma to prevent too many IDLE event trigged if no data
+                 * in RXFIFO
+                 */
                 imx_rx_dma_done(sport);
+        }
 }
 
 static int start_rx_dma(struct imx_port *sport)