linux-kernel - Re: [PATCH v2 1/3] tty: Add functions for handling flow control chars

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Message-ID: <YlAkK16xqh3DgY20@smile.fi.intel.com>
Date:   Fri, 8 Apr 2022 15:01:47 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v2 1/3] tty: Add functions for handling flow control chars

On Fri, Apr 08, 2022 at 02:39:52PM +0300, Ilpo Järvinen wrote:
> Move receive path flow control character handling to own function
> and a helper.
> 
> This seems cleanest approach especially once skipping due to lookahead
> is added. Its downside is the duplicated START_CHAR and STOP_CHAR
> checks.
> 
> No functional changes.

But it seems the change. See below.

...

> +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);

> +	} else if (c == STOP_CHAR(tty)) {

In the original code no 'else' was present.

Perhaps it's not a functional change, but this detail has to be explained.

> +		stop_tty(tty);
> +	}
> +
> +	return true;
> +}

...

> -	if (I_IXON(tty)) {
> -		if (c == START_CHAR(tty)) {
> -			start_tty(tty);
> -			process_echoes(tty);
> -			return;
> -		}
> -		if (c == STOP_CHAR(tty)) {
> -			stop_tty(tty);
> -			return;
> -		}
> -	}
> +	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c))
> +		return;

-- 
With Best Regards,
Andy Shevchenko