From 5688ac95f171c7b1c94fd425504237274ce3ab5b Mon Sep 17 00:00:00 2001 From: Robin Gong Date: Fri, 11 Jul 2014 17:47:17 +0800 Subject: [PATCH] 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. (cherry picked from commit 9271c626e207f9a4578b4696e520253a3bd0ad32) Signed-off-by: Robin Gong Signed-off-by: Fugang Duan --- drivers/tty/serial/imx.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index cf573b1259b7..c272a367b3f4 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -935,8 +935,21 @@ 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) -- 2.39.2