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: 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: In-Reply-To: <200906121015.19504.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 mailing list , LKML List-Id: linux-pm@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? =A0You mean that the PM core shouldn't allow > > devices to suspend unless all their children are suspended? =A0Why > > 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". =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. > = > 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 act= ive > > > 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 bit for > > it in the dev_pm_info structure? > = > Yes. That would resolve the issue. Alan Stern