linux-kernel - Re: [PATCH v2 0/3] led: ledtrig-transient: add support for hrtimer

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Date:   Thu, 14 Sep 2017 10:31:41 -0700
From:   David Lin <dtwlin@...gle.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Jonathan Corbet <corbet@....net>, rpurdie@...ys.net,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        hdegoede@...hat.com, Greg KH <gregkh@...uxfoundation.org>,
        robh@...nel.org, Rom Lemarchand <romlem@...gle.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 0/3] led: ledtrig-transient: add support for hrtimer

On Wed, Sep 13, 2017 at 2:34 PM, Pavel Machek <pavel@....cz> wrote:
>
> On Wed 2017-09-13 14:20:58, David Lin wrote:
> > On Wed, Sep 13, 2017 at 1:20 PM, Pavel Machek <pavel@....cz> 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].
> > >
> > > NAK.
> > >
> > > LEDs do not need extra overhead, and vibrator control should not go
> > > through LED subsystem.
> > >
> > > Input subsystem includes support for vibrations and force
> > > feedback. Please use that instead.
> >
> > I thought we are already over this discussion. As of now, the support
> > of vibrator through ledtrig is documented
> > (Documentation/leds/ledtrig-transient.txt) and there are users using
> > it.
>
> I also thought we are over with that discussion.
>
> Yes, I'm working on fixing the docs.
>
> What mainline users are doing that?

Please refer to patch:
https://patchwork.kernel.org/patch/8664831/ and
https://android.googlesource.com/platform%2Fhardware%2Flibhardware/+/61701df363310a5cbd95e3e1638baa9526e42c9b

I don't think currently there are drivers in the mainline using it
yet, the reason being most of the Android devices are still on 4.4
kernel which still uses the legacy timed_output device.