serial: bfin_sport_uart: shorten the SPORT TX waiting loop

The waiting loop to stop SPORT TX from TX interrupt is too long.  This may
block the SPORT RX interrupts and cause the RX FIFO to overflow. So, do
stop sport TX only after the last char in TX FIFO is moved into the shift
register.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/serial/bfin_sport_uart.c b/drivers/serial/bfin_sport_uart.c
index c88f8ad3ff82..6991c3605f9c 100644
--- a/drivers/serial/bfin_sport_uart.c
+++ b/drivers/serial/bfin_sport_uart.c
@@ -271,7 +271,13 @@ static void sport_uart_tx_chars(struct sport_uart_port *up)
         }
 
         if (uart_circ_empty(xmit) || uart_tx_stopped(&up->port)) {
-                sport_stop_tx(&up->port);
+                /* The waiting loop to stop SPORT TX from TX interrupt is
+                 * too long. This may block SPORT RX interrupts and cause
+                 * RX FIFO overflow. So, do stop sport TX only after the last
+                 * char in TX FIFO is moved into the shift register.
+                 */
+                if (SPORT_GET_STAT(up) & TXHRE)
+                        sport_stop_tx(&up->port);
                 return;
         }