Re: [PATCH] USB: serial: cp210x: map B0 to B9600

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Nov 25, 2022 at 08:58:25PM -0700, Alex Henrie wrote:
> When a baud rate of 0 is requested, both the 8250 driver and the FTDI
> driver reset the baud rate to the default of 9600 (see the comment above
> the uart_get_baud_rate function). Some old versions of the NXP blhost
> utility depend on this behavior. However, the CP210x driver resets the
> baud rate to the minimum supported rate of 300. Special-case B0 so that
> it returns the baud rate to the more sensible default of 9600.
> 
> Signed-off-by: Alex Henrie <alexh@vpitech.com>
> ---
>  drivers/usb/serial/cp210x.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index 3bcec419f463..2c910550dca8 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -1051,9 +1051,14 @@ static void cp210x_change_speed(struct tty_struct *tty,
>  	 * This maps the requested rate to the actual rate, a valid rate on
>  	 * cp2102 or cp2103, or to an arbitrary rate in [1M, max_speed].
>  	 *
> -	 * NOTE: B0 is not implemented.
> +	 * NOTE: B0 is not implemented, apart from returning the baud rate to
> +	 * the default of B9600.
>  	 */
> -	baud = clamp(tty->termios.c_ospeed, priv->min_speed, priv->max_speed);
> +	if (tty->termios.c_ospeed) {
> +		baud = clamp(tty->termios.c_ospeed, priv->min_speed, priv->max_speed);
> +	} else {
> +		baud = 9600;
> +	}

No need for { } here (checkpatch.pl should have warned about this.)

thanks,

greg k-h