Re: [PATCH v4 08/13] USB: ch341: add support for RTS/CTS flow control

Johan Hovold
2016-04-29T13:23:41Z

On Fri, Apr 15, 2016 at 11:14:11PM +0200, Grigori Goronzy wrote:

No commit message?

> v2: use correct flag variable.
> v3: fix compilation
>
> Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
> ---
> drivers/usb/serial/ch341.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
> index e475677..7ca21a1 100644
> --- a/drivers/usb/serial/ch341.c
> +++ b/drivers/usb/serial/ch341.c
> @@ -68,6 +68,7 @@
> #define CH341_REQ_READ_REG 0x95
> #define CH341_REG_BREAK1 0x05
> #define CH341_REG_LCR 0x18
> +#define CH341_REG_RTSCTS 0x27
> #define CH341_NBREAK_BITS_REG1 0x01
>
> #define CH341_LCR_ENABLE_RX 0x80
> @@ -399,6 +400,16 @@ static void ch341_set_termios(struct tty_struct *tty,
>
> ch341_set_handshake(port->serial->dev, priv->line_control);
>
> + if (C_CRTSCTS(tty)) {
> + r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG,
> + CH341_REG_RTSCTS | ((uint16_t)CH341_REG_RTSCTS << 8),

(u16)

> + 0x0101);

You should also coordinate this with B0 handling (e.g. disable
hard-flow control and make sure that RTS is deasserted on ->B0
transitions).

> + if (r < 0) {
> + dev_err(&port->dev, "%s - USB control write error (%d)\n",
> + __func__, r);

Please spell out what went wrong

"failed to enable flow control: %d\n"

> + tty->termios.c_cflag &= ~CRTSCTS;
> + }
> + }

What about disabling flow control?

> }
>
> static void ch341_break_ctl(struct tty_struct *tty, int break_state)

Thanks,
Johan