linux-kernel - Re: [PATCH] USB: serial: cp210x: Workaround for cp2108 failure due to GET_LINE

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Date:	Mon, 19 Oct 2015 11:14:12 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
Cc:	johan@...nel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: cp210x: Workaround for cp2108 failure due
 to GET_LINE_CTL bug

On Thu, 2015-10-15 at 17:06 -0500, Konstantin Shkolnyy wrote:
> cp2108 GET_LINE_CTL returns the 16-bit value with the 2 bytes swapped.
> However, SET_LINE_CTL functions properly. When the driver tries to modify
> the register, it reads it, modifies some bits and writes back. Because the
> read bytes were swapped, this often results in an invalid value to be written.
> In turn, this causes cp2108 respond with a stall. The stall sometimes doesn't
> clear properly and cp2108 starts responding to following valid commands also
> with stalls, effectively failing.

Just a remark.
>  
> @@ -865,18 +888,53 @@ static void cp210x_break_ctl(struct tty_struct *tty, int break_state)
>  
>  static int cp210x_startup(struct usb_serial *serial)
>  {
> +	struct usb_serial_port *port;
>  	struct usb_host_interface *cur_altsetting;
>  	struct cp210x_serial_private *spriv;
> +	unsigned int  line_ctl;
> +	int           err;
> +
> +	/* We always expect a single port only */
> +	if (serial->num_ports != 1) {
> +		dev_err(&serial->dev->dev, "%s - expected 1 port, found %d\n",
> +			__func__, serial->num_ports);
> +		return -EINVAL;
> +	}

Why do you introduce this new check? It has no obvious connect with the
subject of this fix.

	Regards
		Oliver


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