linux-kernel - Re: Vibrations in input vs. LED was Re: [PATCH v2 0/3] led: ledtrig-transient: add support for hrtimer

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Message-ID: <4920a403-3cb3-f34e-12f4-909cb1e128bd@gmail.com>
Date:   Wed, 20 Sep 2017 20:44:44 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     linux-input@...r.kernel.org, David Lin <dtwlin@...gle.com>,
        corbet@....net, rpurdie@...ys.net, hdegoede@...hat.com,
        gregkh@...uxfoundation.org, robh@...nel.org, romlem@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: Vibrations in input vs. LED was Re: [PATCH v2 0/3] led:
 ledtrig-transient: add support for hrtimer

Hi,

On 09/20/2017 01:15 PM, Pavel Machek wrote:
> On Mon 2017-09-18 22:43:40, Jacek Anaszewski wrote:
>> Hi,
>>
>> On 09/17/2017 07:50 PM, Pavel Machek wrote:
>>> Hi!
>>>
>>>>>> Do you think such an improvement could be harmful in some way,
>>>>>> even if it was made optional?
>>>>>
>>>>> Of course, we can make LED timing accurate down to microseconds. It will
>>>>> mean increased overhead -- for "improvement" human can not perceive.
>>>>>
>>>>> If someone has problems with LED delays not being accurate enough... we
>>>>> may want to fix it. But that is not the case here, is it?
>>>>
>>>> AFAIR David was mentioning that the hr_timer support is perceivable
>>>
>>> He said that hr_timer support is perceivable _when he is driving
>>> vibration motor_. Which he should not do in the first place.
>>>
>>> Yes, if the difference is perceivable with LED in non-crazy
>>> configuration (*), we can take the patch. Is it? Do we have someone
>>> not from Google observing it?
>>>
>>> (*) emulating PWM using blink trigger counts as "crazy" :-)
>>
>> How about adding CONFIG_LED_TRIGGERS_HR_TIMER_SUPPORT, guarding the
>> hr timer support in triggers (timer trigger could also benefit from it)
>> with it, and adding "(EXPERIMENTAL)" tag to the config description?
> 
> Why would we want to add code in the LED subsystem that is useless for
> LEDs?

It could be used for software pwm trigger, there has been at least one
an attempt to add such [0].

[0] https://lkml.org/lkml/2015/4/27/493
-- 
Best regards,
Jacek Anaszewski