Re: Modem control lines for RTSCTS hardware flow control via rts-gpio and cts-gpio with IMX

[Sergey Organov <sorganov@gmail.com>]

Tim Harvey <tharvey@gateworks.com> writes:


[...]

> I have found the issue here which causes hardware flow control when
> using GPIO's with the imx UART driver to fail. The
> imx_uart_set_termios() function clears the UCR2_IRTS whenver hardware
> flow control is enabled which configures the transmitter to only send
> with the RTS pin is asserted. In the case of a GPIO being used instead
> of the dedicated internal RTS pin for the uart, this will keep the
> transmitter from ever transmitting. In the hardware flow control case
> where a GPIO is used UCR2_IRTS must be set to ignore the RTS pin. We
> can use the have_rtsgpio flag which is set when 'rts-gpios' property
> is used as a qualifier for this.
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index df8a0c8b8b29..d506cbd679dd 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1674,8 +1674,7 @@ imx_uart_set_termios(struct uart_port *port,
> struct ktermios *termios,
>                 if (ucr2 & UCR2_CTS)
>                         ucr2 |= UCR2_CTSC;
>         }
> -
> -       if (termios->c_cflag & CRTSCTS)
> +       if (!sport->have_rtsgpio && termios->c_cflag & CRTSCTS)
>                 ucr2 &= ~UCR2_IRTS;
>         if (termios->c_cflag & CSTOPB)
>                 ucr2 |= UCR2_STPB;
>
> If this makes sense, I'll send a patch.

To me it does make sense. Driver should stay away from UCR2_IRTS indeed
if software (GPIO) RTS/CTS management is in use.

-- Sergey Organov