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 570df9d..e33d38c 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;
                }