Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759897AbcCDVE6 (ORCPT ); Fri, 4 Mar 2016 16:04:58 -0500 Received: from galahad.ideasonboard.com ([185.26.127.97]:48739 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757489AbcCDVE5 (ORCPT ); Fri, 4 Mar 2016 16:04:57 -0500 From: Laurent Pinchart To: Alan Stern Cc: Ulf Hansson , Laurent Pinchart , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Rafael J. Wysocki" , Len Brown , Pavel Machek , Kevin Hilman , linux-renesas-soc@vger.kernel.org Subject: Re: [PATCH] PM / Runtime: Only force-resume device if it has been force-suspended Date: Fri, 04 Mar 2016 23:04:46 +0200 Message-ID: <1481433.r0tFS4sTcH@avalon> User-Agent: KMail/4.14.8 (Linux/4.1.15-gentoo-r1; KDE/4.14.8; x86_64; ; ) In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3231 Lines: 82 Hi Ulf and Alan, Thank you for the review. On Friday 04 March 2016 10:24:10 Alan Stern wrote: > On Fri, 4 Mar 2016, Ulf Hansson wrote: > > On 3 March 2016 at 21:16, Laurent Pinchart wrote: > >> The pm_runtime_force_suspend() and pm_runtime_force_resume() helpers are > >> designed to help driver being RPM-centric by offering an easy way to > >> manager runtime PM state during system suspend and resume. The first > >> function will force the device into runtime suspend at system suspend > >> time, while the second one will perform the reverse operation at system > >> resume time. > >> > >> However, the pm_runtime_force_resume() really forces resume, regarding > >> of whether the device was running or already suspended before the call > >> to pm_runtime_force_suspend(). This results in devices being runtime > >> resumed at system resume time when they shouldn't. > >> > >> Fix this by recording whether the device has been forcefully suspended > >> in pm_runtime_force_suspend() and condition resume in > >> pm_runtime_force_resume() to that state. > >> > >> All current users of pm_runtime_force_resume() call the function > >> uncontionally in their system resume handler (some actually set it as > >> the resume handler), all after calling pm_runtime_force_suspend() at > >> system suspend time. The change in behaviour should thus be safe. > >> > >> Signed-off-by: Laurent Pinchart > >> > >> > >> @@ -1475,6 +1476,7 @@ int pm_runtime_force_suspend(struct device *dev) > >> goto err; > >> > >> pm_runtime_set_suspended(dev); > >> + dev->power.is_force_suspended = true; > >> return 0; > >> > >> err: > >> pm_runtime_enable(dev); > >> @@ -1510,6 +1515,7 @@ int pm_runtime_force_resume(struct device *dev) > >> if (ret) > >> goto out; > >> > >> + dev->power.is_force_suspended = false; > >> pm_runtime_set_active(dev); > >> pm_runtime_mark_last_busy(dev); > >> out: > > Setting a bitflag is not SMP-safe. When you write to one of the > runtime-PM bits under dev->power, it is necessary to hold > dev->power.lock. > > > Overall I have no objections to this change, as I think it's improving > > the behaviour! > > > > What I was thinking though, but it might be a bit controversial. :-)... > > Instead of relying on whether we actually forced runtime suspend > > earlier, why couldn't we instead check the runtime PM usage count of > > the device? > > > > Only when it's greater than zero, we shall do the forced resume of the > > device, otherwise just re-enable runtime PM. > > > > This would have the affect of leaving devices in runtime suspend, > > until they really needs to be used again. It would thus decrease the > > total system PM resume time. > > > > Do you think this could work? > > If you do this then there would be no need for is_force_suspended. It > seems like a good idea to me. I agree, that's a better idea. Drivers shouldn't call pm_runtime_force_resume() if they haven't called pm_runtime_force_suspend(), so checking the PM use count should be fine. I'll modify the patch, test it and resubmit. -- Regards, Laurent Pinchart