Re: [PATCH v5 2/6] leds: triggers: Add a keyboard backlight trigger

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On 11/24/2016 04:36 PM, Pali Rohár wrote:
> On Thursday 24 November 2016 16:32:06 Jacek Anaszewski wrote:
>> Since it has been reported that POLLPRI notifications on brightness
>> file can lead to increased power consumption, and having my above
>> statement I don't think that it is a good idea to use brightness
>> file for this.
>
> How is brightness file different from others that it cannot issue
> POLLPRI notification?
>
> I understood that problem is there in case that LED level is changed too
> many times per second (like by CPU trigger).
>
> If this is not that problem can you describe real issue, why we cannot
> use POLLPRI for brightness file?

It would be inconsistent not to notify all brightness changes on
brightness file. We should notify all of them or none.

>>> Yes, how triggers interact with brightness file, what happen when you
>>> write 0 on active trigger,
>>
>> There is already a patch in linux-next adding the following:
>>
>>
>> +		Writing 0 to this file clears active trigger.
>> +
>> +		Writing non-zero to this file while trigger is active changes the
>> +		top brightness trigger is going to use.
>> +
>
> Great!
>
>>> what happen when you read brightness file
>>> with active trigger / without trigger.
>>>
>>
>> Yes, this needs to be covered too.
>


-- 
Best regards,
Jacek Anaszewski


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