serial: imx: implement the flush_buffer hook

The current driver does not implement the flush_buffer hook for
uart_ops. When we enable the DMA for the driver, and test it with Bluetooth,
we may meet the following bug for TX:

    [1] User application may call the flush operation at any time.
        The uart_flush_buffer() calls the uart_circ_clear() to set
        the xmit->head and xmit->tail with 0.

    [2] The TX DMA callback can be called at any time too.
        The dma_tx_call() will update the xmit->tail.

    If [2] occurs just after the [1], we will get the wrong xmit->tail.

This patch implements the flush_buffer hook to fix this issue.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index c07d9bb39695..708ba899258d 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1303,6 +1303,16 @@ static void imx_shutdown(struct uart_port *port)
         clk_disable_unprepare(sport->clk_ipg);
 }
 
+static void imx_flush_buffer(struct uart_port *port)
+{
+        struct imx_port *sport = (struct imx_port *)port;
+
+        if (sport->dma_is_enabled) {
+                sport->tx_bytes = 0;
+                dmaengine_terminate_all(sport->dma_chan_tx);
+        }
+}
+
 static void
 imx_set_termios(struct uart_port *port, struct ktermios *termios,
                    struct ktermios *old)
@@ -1623,6 +1633,7 @@ static struct uart_ops imx_pops = {
         .break_ctl      = imx_break_ctl,
         .startup        = imx_startup,
         .shutdown       = imx_shutdown,
+        .flush_buffer   = imx_flush_buffer,
         .set_termios    = imx_set_termios,
         .type           = imx_type,
         .release_port   = imx_release_port,