Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1952694AbdDYWfF (ORCPT ); Tue, 25 Apr 2017 18:35:05 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:42785 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1952657AbdDYWe7 (ORCPT ); Tue, 25 Apr 2017 18:34:59 -0400 Date: Wed, 26 Apr 2017 00:34:55 +0200 From: Pavel Machek To: David Lin Cc: Jacek Anaszewski , rpurdie@rpsys.net, robh@kernel.org, Rom Lemarchand , Joel Fernandes , stable@vger.kernel.org, linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] led: ledtrig-transient: replace timer_list with hrtimer Message-ID: <20170425223455.GA24467@amd> References: <20170424044254.145192-1-dtwlin@google.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="qDbXVdCdHGoSgWSk" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3769 Lines: 101 --qDbXVdCdHGoSgWSk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon 2017-04-24 20:05:59, David Lin wrote: > Hi Jacek, >=20 > On Mon, Apr 24, 2017 at 12:59 PM, Jacek Anaszewski > wrote: > > > > Hi David, > > > > Thanks for the patch. > > > > Unfortunately we cannot switch to using hr timers just like that > > without introducing side effects for many devices. We had similar > > attempt of increasing timer tirgger accuracy two years ago [0]. > > > > In short words, for drivers that can sleep while setting brightness > > and/or are using a bus like I2C you will not be able to enforce > > 1ms delay period. > > > > I recommend you to go through the thread [0] so that we had > > a well defined ground for the discussion on how to address this > > issue properly. > > >=20 > I think I understand the background now, and would agree that not all > the LED driver require hrtimer as human eye can't probably tell > there's a 10ms variation in a blink. However, there's a need to > support hrtimer if the LED subsystem claims support the use case of > vibrator (please see Documentation/leds/ledtrig-transient.txt) as even > a 5ms of variation is perceivable to the user. I'm thinking if a I believe we should fix the documentation. It is LED subsystem, requirements are different, and we _already_ have haptic feedback subsystem. Pavel IOW, I suggest this: (hmm, and more led->LED is needed, and more english fixes. Oh well.) Signed-off-by: Pavel Machek diff --git a/Documentation/leds/ledtrig-transient.txt b/Documentation/leds/= ledtrig-transient.txt index 3bd38b4..c5cf475 100644 --- a/Documentation/leds/ledtrig-transient.txt +++ b/Documentation/leds/ledtrig-transient.txt @@ -16,17 +16,11 @@ set a timer to hold a state, however when user space ap= plication crashes or goes away without deactivating the timer, the hardware will be left in that state permanently. =20 -As a specific example of this use-case, let's look at vibrate feature on -phones. Vibrate function on phones is implemented using PWM pins on SoC or -PMIC. There is a need to activate one shot timer to control the vibrate -feature, to prevent user space crashes leaving the phone in vibrate mode -permanently causing the battery to drain. - Transient trigger addresses the need for one shot timer activation. The transient trigger can be enabled and disabled just like the other leds triggers. =20 -When an led class device driver registers itself, it can specify all leds +When an LED class device driver registers itself, it can specify all leds triggers it supports and a default trigger. During registration, activation routine for the default trigger gets called. During registration of an led class device, the LED state does not change. @@ -144,7 +138,6 @@ repeat the following step as needed: echo none > trigger =20 This trigger is intended to be used for for the following example use case= s: - - Control of vibrate (phones, tablets etc.) hardware by user space app. - Use of LED by user space app as activity indicator. - Use of LED by user space app as a kind of watchdog indicator -- as long as the app is alive, it can keep the LED illuminated, if it di= es --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --qDbXVdCdHGoSgWSk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlj/zw8ACgkQMOfwapXb+vJW7wCfTEmFm2VG+Kn3DxLV79VzcDLz HGQAoKvuxos2ksnqTifRW9UNxPJAhEeb =UBVJ -----END PGP SIGNATURE----- --qDbXVdCdHGoSgWSk--