Hi Sherry, thank you for the fix! On Mon, 2024-03-04 at 10:07 +0800, Sherry Sun wrote: > If the remote uart device is not connected or not enabled after booting > up, the CTS line is high by default. At this time, if we enable the flow > control when opening the device(for example, using “stty -F /dev/ttyLP4 > crtscts” command), there will be a pending idle preamble(first writing 0 > and then writing 1 to UARTCTRL_TE will queue an idle preamble) that > cannot be sent out, resulting in the uart port fail to close(waiting for > TX empty), so the user space stty will have to wait for a long time or > forever. > > This is an LPUART IP bug(idle preamble has higher priority than CTS), > here add a workaround patch to enable TX CTS after enabling UARTCTRL_TE, > so that the idle preamble does not get stuck due to CTS is deasserted. > > Signed-off-by: Sherry Sun <sherry.sun@xxxxxxx> > --- > drivers/tty/serial/fsl_lpuart.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c > index 5ddf110aedbe..dce1b5851de0 100644 > --- a/drivers/tty/serial/fsl_lpuart.c > +++ b/drivers/tty/serial/fsl_lpuart.c > @@ -2345,8 +2345,12 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios, > > lpuart32_write(&sport->port, bd, UARTBAUD); > lpuart32_serial_setbrg(sport, baud); > - lpuart32_write(&sport->port, modem, UARTMODIR); > + /* disable CTS before enabling UARTCTRL_TE to avoid pending idle preamble */ > + lpuart32_write(&sport->port, modem & ~UARTMODIR_TXCTSE, UARTMODIR); > lpuart32_write(&sport->port, ctrl, UARTCTRL); > + /* re-enable the CTS if needed */ > + lpuart32_write(&sport->port, modem, UARTMODIR); > + > /* restore control register */ The fix makes sense to me! I see only one issue with above comment, which commit 380c966c093e7 already have put quite sub-optimal (after the actual write), but your commit now shifts it even further making it completely dangling. Should it be before last UARTCTRL write? > > if ((ctrl & (UARTCTRL_PE | UARTCTRL_M)) == UARTCTRL_PE) -- Alexander Sverdlin Siemens AG www.siemens.com
