From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: [patch update] Re: Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) Date: Wed, 10 Jun 2009 19:42:50 -0400 (EDT) Message-ID: References: <200906110107.23023.oliver@neukum.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <200906110107.23023.oliver@neukum.org> 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: Oliver Neukum Cc: ACPI Devel Maling List , linux-pm@lists.linux-foundation.org, LKML List-Id: linux-pm@vger.kernel.org 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 e= tc., > > the topmost one goes first. =A0The 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 =3D=3D RPM_IDLE > + || dev->parent->power.runtime_status =3D=3D RPM_SUSPENDING > + || dev->parent->power.runtime_status =3D=3D RPM_SUSPENDED))= { > + spin_unlock_irqrestore(&dev->power.lock, flags); > + spin_unlock_irqrestore(&dev->parent->power.lock, parent_f= lags); > + > + /* 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. Alan Stern