From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Lin Subject: Re: [PATCH] led: ledtrig-transient: replace timer_list with hrtimer Date: Mon, 24 Apr 2017 20:05:59 -0700 Message-ID: References: <20170424044254.145192-1-dtwlin@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Received: from mail-yw0-f170.google.com ([209.85.161.170]:34354 "EHLO mail-yw0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S980097AbdDYDGb (ORCPT ); Mon, 24 Apr 2017 23:06:31 -0400 Received: by mail-yw0-f170.google.com with SMTP id k11so43534816ywb.1 for ; Mon, 24 Apr 2017 20:06:31 -0700 (PDT) In-Reply-To: Sender: linux-leds-owner@vger.kernel.org List-Id: linux-leds@vger.kernel.org To: Jacek Anaszewski Cc: rpurdie@rpsys.net, pavel@ucw.cz, robh@kernel.org, Rom Lemarchand , Joel Fernandes , stable@vger.kernel.org, linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org Hi Jacek, 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. > 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 better interim solution is to introduce a LEDS_TRIGGER_TRANSIENT_HRTIMER config to work with both timers in compile time. Would you agree? David