linux-kernel - Re: [PATCH RESEND 3/5] USB: serial: cp210x: Added comments to CRTSCT flag code.

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Date:	Mon, 25 Apr 2016 12:16:35 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
Cc:	johan@...nel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND 3/5] USB: serial: cp210x: Added comments to CRTSCT
 flag code.

On Sun, Apr 24, 2016 at 12:09:21PM -0500, Konstantin Shkolnyy wrote:
> Documented "magic numbers" used in the CRTSCT flag code in terms of
> register bit names from the chip specification.

Documenting these is long overdue. I even started adding defines just to
be able to review the first patch in the series.

> Signed-off-by: Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
> ---
>  drivers/usb/serial/cp210x.c | 38 ++++++++++++++++++++++++++++++++++----
>  1 file changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index ede5c52..b2321a7 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -790,7 +790,7 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
>  
>  	cp210x_read_reg_block(port, CP210X_GET_FLOW, modem_ctl,
>  			sizeof(modem_ctl));
> -	if (modem_ctl[0] & 0x08) {
> +	if (modem_ctl[0] & 0x08) { /* if SERIAL_CTS_HANDSHAKE */

But instead of adding comments like this one and below, please add
proper defines for the various flags and masks. That will make the code
mostly self-explanatory.

>  		dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__);
>  		cflag |= CRTSCTS;
>  	} else {
> @@ -952,17 +952,47 @@ static void cp210x_set_termios(struct tty_struct *tty,
>  			__func__, modem_ctl[0], modem_ctl[4], modem_ctl[7]);
>  
>  		if (cflag & CRTSCTS) {
> -			modem_ctl[0] &= ~0x7B;
> +			modem_ctl[0] &= ~0x7B; /* keep reserved D2 and D7 */
> +			/*
> +			 * D1-D0 SERIAL_DTR_MASK     =01b: DTR is held active
> +			 * D3 SERIAL_CTS_HANDSHAKE   =1: CTS is a handshake line
> +			 * D4 SERIAL_DSR_HANDSHAKE   =0
> +			 * D5 SERIAL_DCD_HANDSHAKE   =0
> +			 * D6 SERIAL_DSR_SENSITIVITY =0
> +			 */

> -		modem_ctl[7] = 0;
> +		modem_ctl[7] = 0; /* SERIAL_XOFF_CONTINUE = 0 */

And this would be better as a bit operation as well (as already
mentioned).

Thanks,
Johan