Path: csiph.com!news.redatomik.org!aioe.org!bofh.it!news.nic.it!robomod From: Geert Uytterhoeven Newsgroups: linux.kernel Subject: [PATCH 2/2] serial: sh-sci: Fix hang in sci_reset() Date: Fri, 02 Dec 2016 13:40:02 +0100 Message-ID: References: X-Original-To: Greg Kroah-Hartman , Jiri Slaby X-Mailer: git-send-email 1.9.1 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 56 Organization: linux.* mail to news gateway X-Original-Cc: Yoshihiro Shimoda , Wolfram Sang , Christoph Baumann , linux-serial@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, Geert Uytterhoeven X-Original-Date: Fri, 2 Dec 2016 13:35:11 +0100 X-Original-Message-ID: <1480682111-9299-3-git-send-email-geert+renesas@glider.be> X-Original-References: <1480682111-9299-1-git-send-email-geert+renesas@glider.be> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1534888 When the .set_termios() callback resets the UART, it first waits until all characters in the transmit FIFO have been transmitted, to prevent a port configuration change from impacting these characters. However, if the previous user of the UART had dedicated RTS/CTS hardware flow control enabled, these characters may have been stuck in the FIFO due to CTS not being asserted. When the new user opens the port, .set_termios() is called while transmission is still disabled, leading to an infinite loop: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! This has been observed with SCIFA (on r8a7740/armadillo) and SCIFB (on r8a7791/koelsch). The issue does not seem to happen when using: - GPIO RTS/CTS hardware flow control, - No hardware flow control, - HSCIF (on r8a7791/koelsch). To fix this, wait for the draining of the transmit FIFO only if transmission is already enabled. Signed-off-by: Geert Uytterhoeven --- To reproduce: stty -echo < /dev/scifb0 stty crtscts < /dev/scifb0 echo hello > /dev/scifb0 # returns early (wrote to FIFO) echo hello > /dev/scifb0 # hangs drivers/tty/serial/sh-sci.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index c503db1900f003ed..db5de80c5399a7bd 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -2137,9 +2137,11 @@ static void sci_reset(struct uart_port *port) const struct plat_sci_reg *reg; unsigned int status; - do { - status = serial_port_in(port, SCxSR); - } while (!(status & SCxSR_TEND(port))); + if (serial_port_in(port, SCSCR) & SCSCR_TE) { + do { + status = serial_port_in(port, SCxSR); + } while (!(status & SCxSR_TEND(port))); + } serial_port_out(port, SCSCR, 0x00); /* TE=0, RE=0, CKE1=0 */ -- 1.9.1