[lkml]   [2009]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    Patch in this message
    Subject[PATCH 8/9] atmel_serial: fix hang in set_termios when crtscts is enabled
    From: Haavard Skinnemoen <>

    After enabling hardware flow control, any subsequent termios call may hang
    waiting for the transmitter to drain. This appears to be caused by a
    busy-loop in set_termios() waiting for the transmitter to become empty,
    which may take a very long time (or hang indefinitely) if the device at
    the other end is blocking us.

    A quick look through the tty and serial_core code indicates that any
    necessary flushing (which is optional) has already been done at this
    point, so there's no need for the driver to flush the transmitter on its

    Fix it by removing the busy-loop altogether.

    Tested-by: Eirik Aanonsen <>
    Signed-off-by: Haavard Skinnemoen <>
    Signed-off-by: Andrew Morton <>
    Signed-off-by: Alan Cox <>

    drivers/serial/atmel_serial.c | 8 +++++---
    1 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
    index b3497d7..338b15c 100644
    --- a/drivers/serial/atmel_serial.c
    +++ b/drivers/serial/atmel_serial.c
    @@ -1104,11 +1104,13 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
    /* update the per-port timeout */
    uart_update_timeout(port, termios->c_cflag, baud);

    - /* save/disable interrupts and drain transmitter */
    + /*
    + * save/disable interrupts. The tty layer will ensure that the
    + * transmitter is empty if requested by the caller, so there's
    + * no need to wait for it here.
    + */
    imr = UART_GET_IMR(port);
    UART_PUT_IDR(port, -1);
    - while (!(UART_GET_CSR(port) & ATMEL_US_TXEMPTY))
    - cpu_relax();

    /* disable receiver and transmitter */

     \ /
      Last update: 2009-06-16 17:07    [W:0.021 / U:0.912 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site