[PATCH 3/8] tty: serial: fsl_lpuart: fix clearing of receive flag

From: Bhuvanchandra DV
Date: Thu Jun 09 2016 - 11:25:57 EST


From: Stefan Agner <stefan.agner@xxxxxxxxxxx>

Commit 8e4934c6d6c6 ("tty: serial: fsl_lpuart: clear receive flag
on FIFO flush") implemented clearing of the receive flag by reading
the status register only. It turned out that even though we flush
the FIFO afterwards, a explicit read of the data register is still
required.

This leads to a FIFO underrun. To avoid this, follow the advice in
the overrun "Operation section": Unconditionally clear RXUF after
using RXFLUSH.

Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
---
drivers/tty/serial/fsl_lpuart.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 75a2098..97c1fda 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -935,13 +935,16 @@ static void lpuart_setup_watermark(struct lpuart_port *sport)
writeb(val | UARTPFIFO_TXFE | UARTPFIFO_RXFE,
sport->port.membase + UARTPFIFO);

- /* explicitly clear RDRF */
- readb(sport->port.membase + UARTSR1);
-
/* flush Tx and Rx FIFO */
writeb(UARTCFIFO_TXFLUSH | UARTCFIFO_RXFLUSH,
sport->port.membase + UARTCFIFO);

+ /* explicitly clear RDRF */
+ if (readb(sport->port.membase + UARTSR1) & UARTSR1_RDRF) {
+ readb(sport->port.membase + UARTDR);
+ writeb(UARTSFIFO_RXUF, sport->port.membase + UARTSFIFO);
+ }
+
writeb(0, sport->port.membase + UARTTWFIFO);
writeb(1, sport->port.membase + UARTRWFIFO);

--
2.8.3