From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: [patch update] Re: [linux-pm] 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: Received: from netrider.rowland.org ([192.131.102.5]:44255 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1758272AbZFJXms (ORCPT ); Wed, 10 Jun 2009 19:42:48 -0400 In-Reply-To: <200906110107.23023.oliver@neukum.org> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Oliver Neukum Cc: "Rafael J. Wysocki" , linux-pm@lists.linux-foundation.org, ACPI Devel Maling List , LKML 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 pare= nt etc., > > the topmost one goes first. =A0The workqueue is singlethread, so > > pm_autoresume() is going to be run for all parents before the devic= e > > itself, so if that were the only resume mechanism, it would be enou= gh to > > check if the parent is RPM_ACTIVE. >=20 > A (IDLE) > / \ > B (SUSPENDED) C (SUSPENDED) >=20 > 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: >=20 > + && (dev->parent->power.runtime_status =3D=3D RPM_IDLE > + || dev->parent->power.runtime_status =3D=3D RPM_SUSPEND= ING > + || dev->parent->power.runtime_status =3D=3D RPM_SUSPEND= ED)) { > + spin_unlock_irqrestore(&dev->power.lock, flags); > + spin_unlock_irqrestore(&dev->parent->power.lock, pare= nt_flags); > + > + /* We have to resume the parent first. */ > + pm_request_resume(dev->parent); >=20 > 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 wil= l > work because C is still in RPM_SUSPENDED. This is an example where usage counters come in handy. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760980AbZFJXm5 (ORCPT ); Wed, 10 Jun 2009 19:42:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759536AbZFJXms (ORCPT ); Wed, 10 Jun 2009 19:42:48 -0400 Received: from netrider.rowland.org ([192.131.102.5]:51386 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1759042AbZFJXms (ORCPT ); Wed, 10 Jun 2009 19:42:48 -0400 Date: Wed, 10 Jun 2009 19:42:50 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Oliver Neukum cc: "Rafael J. Wysocki" , , ACPI Devel Maling List , LKML Subject: Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) In-Reply-To: <200906110107.23023.oliver@neukum.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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 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. Alan Stern