linux-kernel - Re: [PATCH 2/5] leds: triggers: Add a led_trigger_event

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Date:	Wed, 6 Apr 2016 01:38:18 -0300
From:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:	Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:	linux-leds@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Jacek Anaszewski <j.anaszewski@...sung.com>
Subject: Re: [PATCH 2/5] leds: triggers: Add a led_trigger_event_nosleep API

On 5 April 2016 at 18:36, Jacek Anaszewski <jacek.anaszewski@...il.com> wrote:
> Hi Ezequiel,
>
>
> On 04/04/2016 10:22 PM, Ezequiel Garcia wrote:
>>
>> Now that we can mark any LED (even those in use by delayed blink
>> triggers) to trigger on a kernel panic, let's introduce a nosleep
>> led_trigger_event API.
>>
>> This API is needed to skip the delayed blink path on
>> led_trigger_event. LEDs that are switched on a kernel panic,
>> might be in use by a delayed blink trigger.
>>
>> This will be used by the panic LED trigger.
>>
>> Signed-off-by: Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
>> ---
>>   drivers/leds/led-triggers.c | 26 ++++++++++++++++++++++----
>>   include/linux/leds.h        |  4 ++++
>>   2 files changed, 26 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
>> index f5c9d7c4d181..00b9d8497777 100644
>> --- a/drivers/leds/led-triggers.c
>> +++ b/drivers/leds/led-triggers.c
>> @@ -307,8 +307,9 @@ EXPORT_SYMBOL_GPL(devm_led_trigger_register);
>>
>>   /* Simple LED Tigger Interface */
>>
>> -void led_trigger_event(struct led_trigger *trig,
>> -                       enum led_brightness brightness)
>> +static void do_led_trigger_event(struct led_trigger *trig,
>> +                                enum led_brightness brightness,
>> +                                bool nosleep)
>>   {
>>         struct led_classdev *led_cdev;
>>
>> @@ -316,12 +317,29 @@ void led_trigger_event(struct led_trigger *trig,
>>                 return;
>>
>>         read_lock(&trig->leddev_list_lock);
>> -       list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list)
>> -               led_set_brightness(led_cdev, brightness);
>
>
> led_set_brightness() can gently disable blinking if passed 0 in the
> brightness argument. IMHO this patch is not needed then.
>
>

Yes, but the blinking disable is deferred, and so might never
run (e.g. I'd say it won't run on a non-preemptible kernel).

I think we need this API, or otherwise some way of circumventing
the deferred path on led_set_brightness. For instance, we
could turn off delay_on and delay_off in the panic atomic notifier.

I'm not strongly convinced by any approach, but this API seemed
slightly cleaner.
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar