From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754285AbZBQX1Y (ORCPT ); Tue, 17 Feb 2009 18:27:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754291AbZBQX1J (ORCPT ); Tue, 17 Feb 2009 18:27:09 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:36020 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754253AbZBQX1G (ORCPT ); Tue, 17 Feb 2009 18:27:06 -0500 From: "Rafael J. Wysocki" To: Alan Stern Subject: Re: [RFD] Automatic suspend Date: Wed, 18 Feb 2009 00:26:53 +0100 User-Agent: KMail/1.11.0 (Linux/2.6.29-rc5-tst; KDE/4.2.0; x86_64; ; ) Cc: Arjan van de Ven , pm list , LKML , Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= , Benjamin Herrenschmidt , Pavel Machek , Nigel Cunningham , Matthew Garrett , mark gross , "Woodruff, Richard" , Uli Luckas , Igor Stoppa , Brian Swetland , Len Brown References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200902180026.55533.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 17 February 2009, Alan Stern wrote: > On Tue, 17 Feb 2009, Rafael J. Wysocki wrote: > > > On Monday 16 February 2009, Alan Stern wrote: > > > On Mon, 16 Feb 2009, Rafael J. Wysocki wrote: > > > > > > > OK, so I think there are two things that user space may be allowed to do as > > > > far as putting devices into low power states is concerned: > > > > * disable/enable the automatic power management of the device (provided that > > > > the driver supports the automatic PM) > > > > > > Set the automatic PM parameters (idle timeout, state to go to, etc.). > > > > Yes. I'm not sure about the state part, though. > > Maybe, maybe not. IMO it's too early to tell whether anyone will need > this ability, so we shouldn't rule it out. > > > > What about situations where we want to distinguish between the power > > > state of the device itself and the power state of the link? For a disk > > > drive we may want to power the link on and off quite a lot, as that > > > has low latency, but spinning the disk up and down takes a long time > > > and so should have a longer idle-time value. > > > > Well, I'm not sure at the moment. > > > > Do you have any suggestions? > > Not very well fleshed-out ones. I've got a vague idea for allowing a > disk to have a 3-level power arrangement: full power, link disabled but > drive still spinning, and device suspended. I was thinking about that too. > Arranging for automatic transitions among those states will be a little > clumsy but it can be done. As an example of the clumsiness, this scheme > requires that the drive has _two_ idle-timeout values, one for the link and > one for the drive itself. Well, this generally is the case for PCI devices supporting more than two power states. > Another possibility is to set up independent runtime PM for the > transport and the device. This means allowing the possibility that the > transport is suspended while its child (the device) is not. This is a > little simpler (there's only one idle-timeout per device, since the > link is treated as an independent device), but it violates the > principle of never suspending a parent while there is an active child. Well, I think the first approach would be better. Thanks, Rafael