From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Sasha Levin To: stable@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Stefan Agner , Bhuvanchandra DV , Greg Kroah-Hartman , Sasha Levin Subject: [PATCH AUTOSEL 3.18 64/98] tty: serial: fsl_lpuart: fix clearing of receive flag Date: Thu, 25 Oct 2018 10:18:19 -0400 Message-Id: <20181025141853.214051-64-sashal@kernel.org> In-Reply-To: <20181025141853.214051-1-sashal@kernel.org> References: <20181025141853.214051-1-sashal@kernel.org> List-ID: From: Stefan Agner [ Upstream commit d68827c62a105eec547945daedf4d1d3e283717d ] 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 Signed-off-by: Bhuvanchandra DV Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- 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 af3047d8322a..92b7a5bf7c4d 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -910,13 +910,16 @@ 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); -- 2.17.1