linux-kernel - Re: [PATCH 1/5] leds: triggers: Allow to switch the trigger to "panic" on a kernel panic

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Date:	Sun, 24 Apr 2016 11:29:51 +0200
From:	Pavel Machek <pavel@....cz>
To:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:	linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Richard Purdie <rpurdie@...ys.net>,
	Jacek Anaszewski <j.anaszewski@...sung.com>
Subject: Re: [PATCH 1/5] leds: triggers: Allow to switch the trigger to
 "panic" on a kernel panic

On Sun 2016-04-24 11:25:51, Pavel Machek wrote:
> On Mon 2016-04-04 17:22:02, Ezequiel Garcia wrote:
> > This commit adds a new led_cdev flag LED_BLINK_AT_PANIC, which
> > allows to mark a specific LED to be switched to the "panic"
> > trigger, on a kernel panic.
> > 
> > This is useful to allow the user to assign a regular trigger
> > to a given LED, and still blink that LED on a kernel panic.
> > 
> > Signed-off-by: Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
> 
> 
> >  drivers/leds/led-triggers.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/leds.h        |  1 +
> 
> Could we get this out of the core? I'm pretty sure most users are not
> interested...

Thinking about it some more....

This is not really a trigger. This is very special. Maybe hard-coded
handling, like we do for keyboard leds on x86 would be suitable?


> 
> 								Pavel
> 								
> > +/*
> > + * This is a called in a special context by the atomic panic
> > + * notifier. This means the trigger can be changed without
> > + * worrying about locking.
> > + */
> > +static void led_trigger_set_panic(struct led_classdev *led_cdev)
> > +{
> > +	struct led_trigger *trig;
> > +
> > +	list_for_each_entry(trig, &trigger_list, next_trig) {
> > +		if (strcmp("panic", trig->name))
> > +			continue;
> > +		if (led_cdev->trigger)
> > +			list_del(&led_cdev->trig_list);
> > +		list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
> > +		led_cdev->trigger = trig;
> > +		if (trig->activate)
> > +			trig->activate(led_cdev);
> > +		break;
> > +	}
> > +}
> > +
> > +static int led_trigger_panic_notifier(struct notifier_block *nb,
> > +				      unsigned long code, void *unused)
> > +{
> > +	struct led_classdev *led_cdev;
> > +
> > +	list_for_each_entry(led_cdev, &leds_list, node)
> > +		if (led_cdev->flags & LED_BLINK_AT_PANIC)
> > +			led_trigger_set_panic(led_cdev);
> > +	return NOTIFY_DONE;
> > +}
> > +
> > +static struct notifier_block led_trigger_panic_nb = {
> > +	.notifier_call = led_trigger_panic_notifier,
> > +};
> > +
> >  void led_trigger_set_default(struct led_classdev *led_cdev)
> >  {
> >  	struct led_trigger *trig;
> > @@ -356,6 +393,21 @@ void led_trigger_unregister_simple(struct led_trigger *trig)
> >  }
> >  EXPORT_SYMBOL_GPL(led_trigger_unregister_simple);
> >  
> > +static int __init leds_trigger_init(void)
> > +{
> > +	atomic_notifier_chain_register(&panic_notifier_list,
> > +				       &led_trigger_panic_nb);
> > +	return 0;
> > +}
> > +
> > +static void __exit leds_trigger_exit(void)
> > +{
> > +	atomic_notifier_chain_unregister(&panic_notifier_list,
> > +					 &led_trigger_panic_nb);
> > +}
> > +module_init(leds_trigger_init);
> > +module_exit(leds_trigger_exit);
> > +
> >  MODULE_AUTHOR("Richard Purdie");
> >  MODULE_LICENSE("GPL");
> >  MODULE_DESCRIPTION("LED Triggers Core");
> > diff --git a/include/linux/leds.h b/include/linux/leds.h
> > index f203a8f89d30..7f1428bb1e69 100644
> > --- a/include/linux/leds.h
> > +++ b/include/linux/leds.h
> > @@ -50,6 +50,7 @@ struct led_classdev {
> >  #define LED_SYSFS_DISABLE	(1 << 22)
> >  #define LED_DEV_CAP_FLASH	(1 << 23)
> >  #define LED_HW_PLUGGABLE	(1 << 24)
> > +#define LED_BLINK_AT_PANIC	(1 << 25)
> >  
> >  	/* Set LED brightness level
> >  	 * Must not sleep. Use brightness_set_blocking for drivers
> 

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