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From: David Lin <dtwlin@google.com>
Date: Thu, 14 Sep 2017 10:31:41 -0700
Message-ID: <CAPzFB+XrhAUE3Qd+bicCCPk6V7xq7BV=90y=KXudZmGDaS2+cA@mail.gmail.com>
Subject: Re: [PATCH v2 0/3] led: ledtrig-transient: add support for hrtimer
To: Pavel Machek <pavel@ucw.cz>
Cc: Jonathan Corbet <corbet@lwn.net>, rpurdie@rpsys.net,
        Jacek Anaszewski <jacek.anaszewski@gmail.com>, hdegoede@redhat.com,
        Greg KH <gregkh@linuxfoundation.org>, robh@kernel.org,
        Rom Lemarchand <romlem@google.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org
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On Wed, Sep 13, 2017 at 2:34 PM, Pavel Machek <pavel@ucw.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@ucw.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.