Re: [PATCH 0/3] led: ledtrig-transient: add support for hrtimer

From	Jacek Anaszewski <jacek.anaszewski@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/3] led: ledtrig-transient: add support for hrtimer
Date	2017-05-09 22:50 +0200
Message-ID	<tFkeZ-6Un-5@gated-at.bofh.it> (permalink)
References	<tC4Jr-8ub-11@gated-at.bofh.it> <tEY4O-I2-25@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 05/08/2017 11:06 PM, Pavel Machek wrote:
> On Sun 2017-04-30 14:36:58, David Lin wrote:
>> Hi,
>>
>> These patch series add the LED_BRIGHTNESS_FAST flag support for
>> ledtrig-transient to use hrtimer so that platforms with high-resolution timer
>> support can have better accuracy in the trigger duration timing. The need for
>> this support is driven by the fact that Android has removed the timed_ouput [1]
>> and is now using led-trigger for handling vibrator control which requires the
>> timer to be accurate up to a millisecond. However, this flag support would also
>> allow hrtimer to co-exist with the ktimer without causing warning to the
>> existing drivers [2].
> 
> Yes, and objection still stands: You are misusing LED subsystem for
> vibration motors. We already have support for haptic feedback in input
> subsystem.

Regardless of whether it is a misuse or not (ledtrig-transient
documentation suggests that it is one of use cases) we have to keep
it as it has been around for a long time and it has userspace users [0].

Moreover there seems to be broad consensus about it among kernel
people [1].


[0]
https://android.googlesource.com/platform%2Fhardware%2Flibhardware/+/61701df363310a5cbd95e3e1638baa9526e42c9b
[1] https://patchwork.kernel.org/patch/8664831/

-- 
Best regards,
Jacek Anaszewski

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[PATCH 0/3] led: ledtrig-transient: add support for hrtimer David Lin <dtwlin@google.com> - 2017-04-30 23:40 +0200
  [PATCH 2/3] leds: Add the LED_BRIGHTNESS_FAST flag David Lin <dtwlin@google.com> - 2017-04-30 23:40 +0200
  Re: [PATCH 0/3] led: ledtrig-transient: add support for hrtimer David Lin <dtwlin@google.com> - 2017-05-04 02:30 +0200
  Re: [PATCH 0/3] led: ledtrig-transient: add support for hrtimer Pavel Machek <pavel@ucw.cz> - 2017-05-08 23:10 +0200
    Re: [PATCH 0/3] led: ledtrig-transient: add support for hrtimer Jacek Anaszewski <jacek.anaszewski@gmail.com> - 2017-05-09 22:50 +0200

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