Hi Geert, Thank you for the patch.
On Friday 02 Dec 2016 13:35:11 Geert Uytterhoeven wrote: > 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 <[email protected]> > --- > 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))); Won't we still loop forever if the remote side never asserts CTS ? > + } > > serial_port_out(port, SCSCR, 0x00); /* TE=0, RE=0, CKE1=0 */ -- Regards, Laurent Pinchart
