Re: [PATCH 5/5] tty: serial: uartlite: Prevent changing fixed parameters

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jul 23, 2021 at 06:31:51PM -0400, Sean Anderson wrote:
> This device does not support changing baud, parity, data bits, stop
> bits, or detecting breaks. Disable "changing" these settings to prevent
> their termios from diverging from the actual state of the uart. To inform
> users of these limitations, warn if the new termios change these
> parameters. We only do this once to avoid spamming the log. These
> warnings are inspired by those in the sifive driver.
> 
> Signed-off-by: Sean Anderson <sean.anderson@seco.com>
> ---
> 
>  drivers/tty/serial/uartlite.c | 52 +++++++++++++++++++++++++++++++++--
>  1 file changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c
> index 39c17ab206ca..0aed70039f46 100644
> --- a/drivers/tty/serial/uartlite.c
> +++ b/drivers/tty/serial/uartlite.c
> @@ -314,7 +314,54 @@ static void ulite_set_termios(struct uart_port *port, struct ktermios *termios,
>  			      struct ktermios *old)
>  {
>  	unsigned long flags;
> -	unsigned int baud;
> +	struct uartlite_data *pdata = port->private_data;
> +	tcflag_t old_cflag;
> +
> +	if (termios->c_iflag & BRKINT)
> +		dev_err_once(port->dev, "BREAK detection not supported\n");
> +	termios->c_iflag &= ~BRKINT;
> +
> +	if (termios->c_cflag & CSTOPB)
> +		dev_err_once(port->dev, "only one stop bit supported\n");
> +	termios->c_cflag &= ~CSTOPB;
> +
> +	old_cflag = termios->c_cflag;
> +	termios->c_cflag &= ~(PARENB | PARODD);
> +	if (pdata->parity == 'e')
> +		termios->c_cflag |= PARENB;
> +	else if (pdata->parity == 'o')
> +		termios->c_cflag |= PARENB | PARODD;
> +
> +	if (termios->c_cflag != old_cflag)
> +		dev_err_once(port->dev, "only '%c' parity supported\n",
> +			     pdata->parity);

Through all of this, you are warning that nothing is supported, yet you
are continuing on as if all of this worked just fine.

That feels odd, why is this needed at all?  If you really do not support
any changes here, why even fake it?

thanks,

greg k-h