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

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Message-id: <571DBFAE.7060605@samsung.com>
Date:	Mon, 25 Apr 2016 08:56:46 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
	linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH 1/5] leds: triggers: Allow to switch the trigger to "panic"
 on a kernel panic

On 04/24/2016 11:29 AM, Pavel Machek wrote:
> 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...

Good point.

> 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?

Could you please spot the piece of code you have on mind?

>
>
>>
>> 								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
>>
>


-- 
Best regards,
Jacek Anaszewski