From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Stefan Agner , Bhuvanchandra DV , Sasha Levin Subject: [PATCH 3.18 093/144] tty: serial: fsl_lpuart: fix clearing of receive flag Date: Thu, 8 Nov 2018 13:51:04 -0800 Message-Id: <20181108215103.075842925@linuxfoundation.org> In-Reply-To: <20181108215054.826084593@linuxfoundation.org> References: <20181108215054.826084593@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit List-ID: 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ [ 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