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

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Date:	Fri, 29 Apr 2016 15:23:39 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Grigori Goronzy <greg@...wn.ath.cx>
Cc:	Johan Hovold <johan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 08/13] USB: ch341: add support for RTS/CTS flow control

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@...wn.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