serial: imx: check the DMA for imx_tx_empty

Assume the following situation:

  If the DMA is enabled, and the a TX DMA operation is working,
But we have not issued the TX DMA operation (or we have issued the
TX DMA operation with dma_async_issue_pending(), but the DMA has not
started to move the data from the memory to the TXFIFO).

At this time, we may get the wrong status of the transmitter when we
call the imx_tx_empty. In such situation, only check the USR2_TXDC
does not enough for us.

This patch checks the DMA's situation, and return 0 when the TX DMA is
working.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 708ba899258d71cef595f893a7bcca9d77bcb3d8..c6c3b160dac763955d44a788f203fd7a4b4dd42c 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -795,8 +795,15 @@ static irqreturn_t imx_int(int irq, void *dev_id)
 static unsigned int imx_tx_empty(struct uart_port *port)
 {
        struct imx_port *sport = (struct imx_port *)port;
+       unsigned int ret;
 
-       return (readl(sport->port.membase + USR2) & USR2_TXDC) ?  TIOCSER_TEMT : 0;
+       ret = (readl(sport->port.membase + USR2) & USR2_TXDC) ?  TIOCSER_TEMT : 0;
+
+       /* If the TX DMA is working, return 0. */
+       if (sport->dma_is_enabled && sport->dma_is_txing)
+               ret = 0;
+
+       return ret;
 }
 
 /*