linux-kernel - Re: [PATCH v5 3/3] USB: serial: cp210x: New access functions for large registers

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Message-ID: <20160229103601.GE26559@localhost>
Date:	Mon, 29 Feb 2016 11:36:01 +0100
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 v5 3/3] USB: serial: cp210x: New access functions for
 large registers

On Sun, Feb 28, 2016 at 03:51:56PM -0600, Konstantin Shkolnyy wrote:
> cp210x_get_config and cp210x_set_config are cumbersome to use. This change
> switches large register access to use new block functions. The old
> functions are removed because now they become unused.
> 
> Signed-off-by: Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
> ---

> @@ -886,8 +788,9 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
>  		break;
>  	}
>  
> -	cp210x_get_config(port, CP210X_GET_FLOW, modem_ctl, 16);
> -	if (modem_ctl[0] & 0x0008) {
> +	cp210x_read_reg_block(port, CP210X_GET_FLOW, modem_ctl,
> +			sizeof(modem_ctl));
> +	if (modem_ctl[0] & 8) {

I changed this to 0x08 as it's a bitmask.

>  		dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__);
>  		cflag |= CRTSCTS;
>  	} else {
> @@ -956,7 +859,7 @@ static void cp210x_set_termios(struct tty_struct *tty,
>  	struct device *dev = &port->dev;
>  	unsigned int cflag, old_cflag;
>  	u16 bits;
> -	unsigned int modem_ctl[4];
> +	u8 modem_ctl[16];
>  
>  	cflag = tty->termios.c_cflag;
>  	old_cflag = old_termios->c_cflag;
> @@ -1040,27 +943,35 @@ static void cp210x_set_termios(struct tty_struct *tty,
>  	}
>  
>  	if ((cflag & CRTSCTS) != (old_cflag & CRTSCTS)) {
> -		cp210x_get_config(port, CP210X_GET_FLOW, modem_ctl, 16);
> -		dev_dbg(dev, "%s - read modem controls = 0x%.4x 0x%.4x 0x%.4x 0x%.4x\n",
> -			__func__, modem_ctl[0], modem_ctl[1],
> -			modem_ctl[2], modem_ctl[3]);
> +
> +		/* Only bytes 0, 4 and 7 out of first 8 have functional bits */
> +
> +		cp210x_read_reg_block(port, CP210X_GET_FLOW, modem_ctl,
> +				sizeof(modem_ctl));
> +		dev_dbg(dev, "%s - read modem controls = %02x .. .. .. %02x .. .. %02x\n",
> +			__func__, modem_ctl[0], modem_ctl[4], modem_ctl[7]);

And here you're actually now leaving out XON/XOFF limits in the last 8
bytes. It would have been better to just dump the whole array and make
any such changes explicitly in a separate patch, but I left this in this
time.

>  		if (cflag & CRTSCTS) {
>  			modem_ctl[0] &= ~0x7B;
>  			modem_ctl[0] |= 0x09;
> -			modem_ctl[1] = 0x80;
> +			modem_ctl[4] = 0x80;
> +			/* FIXME - why clear reserved bits just read? */
> +			modem_ctl[5] = 0;
> +			modem_ctl[6] = 0;
> +			modem_ctl[7] = 0;
>  			dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__);
>  		} else {
>  			modem_ctl[0] &= ~0x7B;
>  			modem_ctl[0] |= 0x01;
> -			modem_ctl[1] |= 0x40;
> +			/* FIXME - OR here instead of assignment looks wrong */
> +			modem_ctl[4] |= 0x40;

These indeed looks like bugs, but I agree that fixing the accessor
functions first made sense.

Looking forward to the follow-up fixes. :)

All three patches now applied.

Thanks for sticking to this.

Johan