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: Fri, 12 Jun 2009 10:32:02 -0400 (EDT) Message-ID: References: <200906121015.19504.oliver@neukum.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from iolanthe.rowland.org ([192.131.102.54]:32884 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755048AbZFLOcA (ORCPT ); Fri, 12 Jun 2009 10:32:00 -0400 In-Reply-To: <200906121015.19504.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 mailing list , ACPI Devel Maling List , LKML On Fri, 12 Jun 2009, Oliver Neukum wrote: > Am Freitag, 12. Juni 2009 04:16:10 schrieb Alan Stern: > > What tree constraint? =A0You mean that the PM core shouldn't allow > > devices to suspend unless all their children are suspended? =A0Why > > doesn't it still apply? >=20 > Because the hardware doesn't need it. But maybe drivers need it. > > Remember, when Rafael and I say "suspend" here, we don't mean "go t= o a > > low-power state". =A0We mean "the PM core calls the runtime_suspend > > method". =A0No matter what actions the link hardware may decide to = take > > on its own, the PM core will still want to observe the > > all-children-suspended restriction when calling runtime_suspend > > methods. >=20 > No. The core if it insists all children be suspended will not use > the hardware's full capabilities. That isn't what I said. The core does not insist that all children be=20 suspended, i.e., be in a low-power state. It insists only that the=20 children's drivers' runtime_suspend methods have been called. Those=20 methods are not obligated to put the children in a low-power state. > If it leaves such power saving measures to the drivers, latency > accounting will be wrong. >=20 > > > I think there are devices who can be suspended while children are= active > > > and devices which can not be. This is an attribute of the device = and > > > should be evaluated by the core. > > > > Clearly it should be decided by the driver. =A0Should there be a bi= t for > > it in the dev_pm_info structure? >=20 > Yes. That would resolve the issue. 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 S932194AbZFLOcU (ORCPT ); Fri, 12 Jun 2009 10:32:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758890AbZFLOcB (ORCPT ); Fri, 12 Jun 2009 10:32:01 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:32885 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754921AbZFLOcA (ORCPT ); Fri, 12 Jun 2009 10:32:00 -0400 Date: Fri, 12 Jun 2009 10:32:02 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: "Rafael J. Wysocki" , Linux-pm mailing list , 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: <200906121015.19504.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 Fri, 12 Jun 2009, Oliver Neukum wrote: > Am Freitag, 12. Juni 2009 04:16:10 schrieb Alan Stern: > > What tree constraint?  You mean that the PM core shouldn't allow > > devices to suspend unless all their children are suspended?  Why > > doesn't it still apply? > > Because the hardware doesn't need it. But maybe drivers need it. > > Remember, when Rafael and I say "suspend" here, we don't mean "go to a > > low-power state".  We mean "the PM core calls the runtime_suspend > > method".  No matter what actions the link hardware may decide to take > > on its own, the PM core will still want to observe the > > all-children-suspended restriction when calling runtime_suspend > > methods. > > No. The core if it insists all children be suspended will not use > the hardware's full capabilities. That isn't what I said. The core does not insist that all children be suspended, i.e., be in a low-power state. It insists only that the children's drivers' runtime_suspend methods have been called. Those methods are not obligated to put the children in a low-power state. > If it leaves such power saving measures to the drivers, latency > accounting will be wrong. > > > > I think there are devices who can be suspended while children are active > > > and devices which can not be. This is an attribute of the device and > > > should be evaluated by the core. > > > > Clearly it should be decided by the driver.  Should there be a bit for > > it in the dev_pm_info structure? > > Yes. That would resolve the issue. Alan Stern