From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [patch update] Re: Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) Date: Thu, 11 Jun 2009 15:48:33 +0200 Message-ID: <200906111548.33751.rjw__9748.05057417161$1244728128$gmane$org@sisk.pl> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: Alan Stern Cc: ACPI Devel Maling List , linux-pm@lists.linux-foundation.org, LKML List-Id: linux-pm@vger.kernel.org On Thursday 11 June 2009, Alan Stern wrote: > On Thu, 11 Jun 2009, Oliver Neukum wrote: > > > Am Donnerstag, 11. Juni 2009 00:01:20 schrieb Rafael J. Wysocki: > > > We have queued up resume requests for the device's parent, its parent etc., > > > the topmost one goes first. The workqueue is singlethread, so > > > pm_autoresume() is going to be run for all parents before the device > > > itself, so if that were the only resume mechanism, it would be enough to > > > check if the parent is RPM_ACTIVE. > > > > A (IDLE) > > / \ > > B (SUSPENDED) C (SUSPENDED) > > > > Suppose C is to be resumed. This means first in case of A the request > > to suspend would be cancelled. Here you drop the locks: > > > > + && (dev->parent->power.runtime_status == RPM_IDLE > > + || dev->parent->power.runtime_status == RPM_SUSPENDING > > + || dev->parent->power.runtime_status == RPM_SUSPENDED)) { > > + spin_unlock_irqrestore(&dev->power.lock, flags); > > + spin_unlock_irqrestore(&dev->parent->power.lock, parent_flags); > > + > > + /* We have to resume the parent first. */ > > + pm_request_resume(dev->parent); > > > > But after pm_request_resume() returns there's no means to make sure > > nothing alters it back to RPM_SUSPENDED. The workqueue doesn't help > > you because you've scheduled nothing by that time. The suspension will > > work because C is still in RPM_SUSPENDED. > > This is an example where usage counters come in handy. Do you mean we can count suspend/resume requests for a device? Rafael