serial: 8250: don't change the fifo trigger level when using dma

DMA engines usually expect the fifo trigger level to be
aligned with the burst size. It should not be changed even
with small baud rates. This will fix an issue with
Designware DMA engine where the data can not be transferred
over UART with lower baud rates then 2400.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 570df9d2a5d2f46afc72a23d1e373f2c5aa4f3ba..e33d38cb170f97e4055a0a17eb0f4e7bc0b45d0e 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -2322,7 +2322,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 
        if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
                fcr = uart_config[port->type].fcr;
-               if (baud < 2400 || fifo_bug) {
+               if ((baud < 2400 && !up->dma) || fifo_bug) {
                        fcr &= ~UART_FCR_TRIGGER_MASK;
                        fcr |= UART_FCR_TRIGGER_1;
                }