linux-kernel - Re: [PATCH v5 3/3] leds: trigger: implement a tty trigger

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Date:   Sat, 21 Dec 2019 19:40:47 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Dan Murphy <dmurphy@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v5 3/3] leds: trigger: implement a tty trigger

Hi!

> +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
> @@ -0,0 +1,6 @@
> +What:		/sys/class/leds/<led>/dev
> +Date:		Dec 2019
> +KernelVersion:	5.6
> +Contact:	linux-leds@...r.kernel.org
> +Description:
> +		Specifies $major:$minor of the triggering tty

Ok, sounds reasonable.

> +static ssize_t dev_store(struct device *dev,
> +			 struct device_attribute *attr, const char *buf,
> +			 size_t size)
> +{
> +	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
> +	struct tty_struct *tty;
> +	unsigned major, minor;
> +	int ret;
> +
> +	if (size == 0 || (size == 1 && buf[0] == '\n')) {
> +		tty = NULL;
> +	} else {
> +		ret = sscanf(buf, "%u:%u", &major, &minor);
> +		if (ret < 2)
> +			return -EINVAL;

If user writes 1:2:badparsingofdata into the file, it will pass, right?

> +		tty = tty_kopen_shared(MKDEV(major, minor));
> +		if (IS_ERR(tty))
> +			return PTR_ERR(tty);
> +	}

Do you need to do some kind of tty_kclose()? What happens if the
device disappears, for example because the USB modem is unplugged?

> +static void ledtrig_tty_work(struct work_struct *work)
> +{
> +	struct ledtrig_tty_data *trigger_data =
> +		container_of(work, struct ledtrig_tty_data, dwork.work);
> +	struct serial_icounter_struct icount;
> +	int ret;
> +
> +	if (!trigger_data->tty) {
> +		led_set_brightness(trigger_data->led_cdev, LED_OFF);
> +		return;
> +	}
> +
> +	ret = tty_get_icount(trigger_data->tty, &icount);
> +	if (ret)
> +		return;
> +
> +	if (icount.rx != trigger_data->rx ||
> +	    icount.tx != trigger_data->tx) {
> +		unsigned long delay_on = 100, delay_off = 100;
> +
> +		led_blink_set_oneshot(trigger_data->led_cdev,
> +				      &delay_on, &delay_off, 0);
> +
> +		trigger_data->rx = icount.rx;
> +		trigger_data->tx = icount.tx;
> +	}

Since you are polling this, anyway, can you just manipulate brightness
directly instead of using _oneshot()? _oneshot() will likely invoke
another set of workqueues.

LED triggers were meant to operate directly from the events, not based
on statistics like this.

Best regards,

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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