| Message ID | 20240305015706.1050769-1-sherry.sun@nxp.com |
|---|---|
| State | New |
| Headers | show |
| Series | [V2] tty: serial: fsl_lpuart: avoid idle preamble pending if CTS is enabled | expand |
Hi Sherry, thanks for re-spin! On Tue, 2024-03-05 at 09:57 +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. > > Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support") > Signed-off-by: Sherry Sun <sherry.sun@nxp.com> Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com> > --- > Changes in V2: > 1. Move the "restore control register" comment message to the appropriate place. > 2. Add Fixes tag. > --- > drivers/tty/serial/fsl_lpuart.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c > index 5ddf110aedbe..bbcbc91482af 100644 > --- a/drivers/tty/serial/fsl_lpuart.c > +++ b/drivers/tty/serial/fsl_lpuart.c > @@ -2345,9 +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); > - lpuart32_write(&sport->port, ctrl, UARTCTRL); > + /* disable CTS before enabling UARTCTRL_TE to avoid pending idle preamble */ > + lpuart32_write(&sport->port, modem & ~UARTMODIR_TXCTSE, UARTMODIR); > /* restore control register */ > + lpuart32_write(&sport->port, ctrl, UARTCTRL); > + /* re-enable the CTS if needed */ > + lpuart32_write(&sport->port, modem, UARTMODIR); > > if ((ctrl & (UARTCTRL_PE | UARTCTRL_M)) == UARTCTRL_PE) > sport->is_cs7 = true;
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 5ddf110aedbe..bbcbc91482af 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -2345,9 +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); - lpuart32_write(&sport->port, ctrl, UARTCTRL); + /* disable CTS before enabling UARTCTRL_TE to avoid pending idle preamble */ + lpuart32_write(&sport->port, modem & ~UARTMODIR_TXCTSE, UARTMODIR); /* restore control register */ + lpuart32_write(&sport->port, ctrl, UARTCTRL); + /* re-enable the CTS if needed */ + lpuart32_write(&sport->port, modem, UARTMODIR); if ((ctrl & (UARTCTRL_PE | UARTCTRL_M)) == UARTCTRL_PE) sport->is_cs7 = true;
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. Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support") Signed-off-by: Sherry Sun <sherry.sun@nxp.com> --- Changes in V2: 1. Move the "restore control register" comment message to the appropriate place. 2. Add Fixes tag. --- drivers/tty/serial/fsl_lpuart.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)