From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH] Input: smtpe-ts: Use msecs_to_jiffies() instead of HZ Date: Wed, 6 May 2015 16:59:28 -0700 Message-ID: <20150506235928.GG5580@dtor-ws> References: <1430869596-7044-1-git-send-email-marex@denx.de> <20150506000135.GA25707@dtor-ws> <201505060236.14358.marex@denx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-ig0-f179.google.com ([209.85.213.179]:34845 "EHLO mail-ig0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751403AbbEFX7d (ORCPT ); Wed, 6 May 2015 19:59:33 -0400 Received: by igbyr2 with SMTP id yr2so145832862igb.0 for ; Wed, 06 May 2015 16:59:32 -0700 (PDT) Content-Disposition: inline In-Reply-To: <201505060236.14358.marex@denx.de> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Marek Vasut Cc: linux-input@vger.kernel.org, Vipul Kumar Samar , Viresh Kumar On Wed, May 06, 2015 at 02:36:14AM +0200, Marek Vasut wrote: > On Wednesday, May 06, 2015 at 02:01:35 AM, Dmitry Torokhov wrote: > > On Wed, May 06, 2015 at 01:46:36AM +0200, Marek Vasut wrote: > > > Use msecs_to_jiffies(50) instead of plain (HZ / 50) as the > > > former is independent of kernel HZ settings and provides > > > stable delay. > > > > > > The delay here must be stable, otherwise we might start polling > > > for pen-up event too early. This would in turn render the > > > touchscreen unusable. > > Hi! > > > Doesn't jiffy "size" depend on HZ value? I'd expect the delay be > > "stable" regardless of the value of HZ. > > I have to admit I am not sure, but this would make sense. > > > I do not disagree with the > > patch, but I think you need better justification here (except I think > > the delay should be 20 msec, not 50, and we may use a constant instead > > of reevaluating it all the time). > > Maybe I'm fixing two bugs here ? The problem I really had is that with > kernel HZ set to 250 and the original code, the work was scheduled and > executed too quickly, so my touchscreen was bouncing between pendown and > penup events back and forth, without doing any usaful work. > > I tried changing the code to HZ/5 instead of HZ/50 and that fixes my > issue as well. > > My impression is that using msec_to_jiffies() is clearer especially > if the code is to represent a constant delay. It is indeed clearer and I would not mind such conversion, we just need to adjust the comment why we do that. > But maybe I should then > document why I changed the duration (because the original one was too > short) ? Please make a separate patch for that with separate justification. Thanks! -- Dmitry