linux-kernel - Re: [PATCH v7 2/2] trigger: ledtrig-tty: add additional modes

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Date:   Mon, 6 Mar 2023 10:23:32 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Lee Jones <lee@...nel.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, Florian Eckert <fe@....tdt.de>,
        gregkh@...uxfoundation.org, pavel@....cz,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        Eckert.Florian@...glemail.com
Subject: Re: [PATCH v7 2/2] trigger: ledtrig-tty: add additional modes

On Mon, Mar 06, 2023 at 09:04:56AM +0000, Lee Jones wrote:
> On Mon, 06 Mar 2023, Jiri Slaby wrote:
> 
> > On 03. 03. 23, 15:11, Lee Jones wrote:
> > > On Wed, 22 Feb 2023, Florian Eckert wrote:
> > > > @@ -113,21 +207,38 @@ static void ledtrig_tty_work(struct work_struct *work)
> > > >   		trigger_data->tty = tty;
> > > >   	}
> > > > -	ret = tty_get_icount(trigger_data->tty, &icount);
> > > > -	if (ret) {
> > > > -		dev_info(trigger_data->tty->dev, "Failed to get icount, stopped polling\n");
> > > > -		mutex_unlock(&trigger_data->mutex);
> > > > -		return;
> > > > -	}
> > > > -
> > > > -	if (icount.rx != trigger_data->rx ||
> > > > -	    icount.tx != trigger_data->tx) {
> > > > -		led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
> > > > -
> > > > -		trigger_data->rx = icount.rx;
> > > > -		trigger_data->tx = icount.tx;
> > > > -	} else {
> > > > -		led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
> > > > +	switch (trigger_data->mode) {
> > > > +	case TTY_LED_CTS:
> > > > +		ledtrig_tty_flags(trigger_data, TIOCM_CTS);
> > > > +		break;
> > > > +	case TTY_LED_DSR:
> > > > +		ledtrig_tty_flags(trigger_data, TIOCM_DSR);
> > > > +		break;
> > > > +	case TTY_LED_CAR:
> > > > +		ledtrig_tty_flags(trigger_data, TIOCM_CAR);
> > > > +		break;
> > > > +	case TTY_LED_RNG:
> > > > +		ledtrig_tty_flags(trigger_data, TIOCM_RNG);
> > > > +		break;
> > > > +	case TTY_LED_CNT:
> > > 
> > > I believe this requires a 'fall-through' statement.
> > 
> > I don't think this is the case. Isn't fallthrough required only in cases
> > when there is at least one statement, i.e. a block?
> 
> There's no mention of this caveat in the document.
> 
> To my untrained eyes, the rule looks fairly explicit, starting with "All".
> 
> "
>   All switch/case blocks must end in one of:
> 
>   * break;
>   * fallthrough;
>   * continue;
>   * goto <label>;
>   * return [expression];
> "
> 
> If you're aware of something I'm not, please consider updating the doc.

Just to add my 0.02€: I think this case (i.e.

	case TTY_LED_CNT:
	default:
		...

) doesn't need a fall-through for two reasons:

 a) The compilers don't warn about this construct even with the
    fall-through warning enabled; and
 b) I wouldn't call the TTY_LED_CNT line a "block", so the quoted
    document[1] doesn't apply. (Though I agree that there is some
    potential for improvement by mentioning this case. (haha))

Best regards
Uwe

[1] Documentation/process/deprecated.rst

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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