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 <geert+renesas@xxxxxxxxx>
> ---
> 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
