From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757846Ab3EVWUN (ORCPT ); Wed, 22 May 2013 18:20:13 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:42259 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757834Ab3EVWUK (ORCPT ); Wed, 22 May 2013 18:20:10 -0400 Date: Wed, 22 May 2013 15:20:08 -0700 From: Andrew Morton To: Bernie Thompson Cc: rtc-linux@googlegroups.com, Alessandro Zummo , Rob Landley , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Doug Anderson Subject: Re: [PATCH] rtc: add in ability to push out an existing wakealarm using sysfs Message-Id: <20130522152008.4aeaa834f4d50b750832bd65@linux-foundation.org> In-Reply-To: References: <1368233611-1690-1-git-send-email-bhthompson@chromium.org> <20130522145529.a03f3344f58b4b9ddacb25b7@linux-foundation.org> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 May 2013 15:05:44 -0700 Bernie Thompson wrote: > On Wed, May 22, 2013 at 2:55 PM, Andrew Morton > wrote: > > > > On Fri, 10 May 2013 17:53:31 -0700 Bernie Thompson wrote: > > > > > This adds in the ability for the rtc sysfs code to handle += characters > > > at the beginning of a wakealarm setting string. This will allow the user to > > > attempt to push out an existing wakealarm by a provided amount. > > > > > > In the case that the += characters are provided but the alarm is not active > > > -EVINVAL is returned. > > > > > > > Well that sounds useful, but I'm not personally in a position to > > confidently judge whether it's useful enough to merge the patch. The > > changelog doesn't make a compelling case and everybody else has chosen > > to sit on their hands. > > > > So I really don't know what to do with this patch. > > > > Thank you for looking at this, I was just talking with Doug on CC this > morning about > explaining why this is useful, at least for my purposes in > suspend/resume testing. > The basic test goes something like: > > 1. Set a wake alarm from userspace 5 seconds in the future > > 2. Start the suspend process (echo mem > /sys/power/state) > > 3. After ~2.5 seconds if userspace is still running (using another > thread to check > this), move the wake alarm 5 more seconds > > If the "move" involves an unset of the wakealarm then there's a > period of time where the system is midway through suspending but has > no wake alarm. It will get stuck. > > We'd rather not remove the "move" since the idea is to avoid a > cancelled suspend when the alarm fires _during_ suspend. It is > difficult for the test to tell the difference between a suspend that > was cancelled because the alarm fired too early and a suspend that was > cancelled/failed for some other reason. OK, I'm (easily) convinced. I guess that if the alarm fires right in the middle of rtc_sysfs_set_wakealarm() execution, everything collapses in a heap. Why does the current code "Avoid accidentally clobbering active alarms"?[*] I'd have thought that being able to reset the expiry time of a pending alarm would be rather useful. [*] repeat after me: comments should explain "what", not "why". grr.