linux-kernel - Re: [PATCH v3 2/5] tty: Simplify receive flow control char logic

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Message-ID: <YmK796AkXmoSb5fZ@kroah.com>
Date:   Fri, 22 Apr 2022 16:30:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v3 2/5] tty: Simplify receive flow control char logic

On Mon, Apr 11, 2022 at 12:48:56PM +0300, Ilpo Järvinen wrote:
> Add a helper to check if the character is a flow control one.
> Reorder return places, add else for the case where START_CHAR
> and STOP_CHAR are the same, w/o else both would match.
> 
> This seems cleanest approach once skipping due to lookahead
> is added by the next patch. Its downside is the duplicated
> START_CHAR and STOP_CHAR checks.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  drivers/tty/n_tty.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index c7edfc001fd0..90b3e06cbeb1 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -1220,20 +1220,25 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
>  		process_echoes(tty);
>  }
>  
> +static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
> +{
> +	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
> +}
> +
>  /* Returns true if c is consumed as flow-control character */
>  static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
>  {
> +	if (!n_tty_is_char_flow_ctrl(tty, c))
> +		return false;
> +
>  	if (c == START_CHAR(tty)) {
>  		start_tty(tty);
>  		process_echoes(tty);
> -		return true;
> -	}
> -	if (c == STOP_CHAR(tty)) {
> +	} else if (c == STOP_CHAR(tty)) {

The else is always true here now so why check it again?

Just return in the above if statement and then call stop_tty().

thanks,

greg k-h