From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Neukum Subject: Re: Power management for SCSI Date: Wed, 13 Aug 2008 16:47:42 +0200 Message-ID: <200808131647.43989.oneukum@suse.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Alan Stern Cc: Pavel Machek , kernel list , Linux-pm mailing list , James.Bottomley@hansenpartnership.com, teheo@novell.com List-Id: linux-pm@vger.kernel.org Am Mittwoch 13 August 2008 16:31:03 schrieb Alan Stern: > On Wed, 13 Aug 2008, Pavel Machek wrote: > > > From: Alan Stern > > > > Add support for autosuspend/autoresume. Lowlevel driver can use it to > > spin the disk down and power down its SATA link, to turn off the USB > > interface, etc. > > > > Spinning down the disk is useful - saves ~0.5W here. Powering down > > SATA controller is even better -- should save ~1W. > > > > Now, I guess the patch will need to be split to small pieces for > > merge... I tried to rearrange it so that the documentation and hooks > > go before stuff that needs the hooks, and before Kconfig enabler. If > > it looks reasonably good, I'll split it into smaller pieces. > > James had a number of objections to my original patch; you can read > them here: > > https://lists.linux-foundation.org/pipermail/linux-pm/2008-March/016849.html Very well. I see a basic problem here. For USB it is necessary that child devices be suspended before anything higher up in the tree is suspended. SATA seems to be able to power down a link while the device is not suspended. In fact in true SCSI busses can be shared. So are we using the correct approach? Regards Oliver