Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756001AbYHMPUt (ORCPT ); Wed, 13 Aug 2008 11:20:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753225AbYHMPUk (ORCPT ); Wed, 13 Aug 2008 11:20:40 -0400 Received: from cantor2.suse.de ([195.135.220.15]:58445 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753031AbYHMPUk (ORCPT ); Wed, 13 Aug 2008 11:20:40 -0400 From: Oliver Neukum Organization: Novell To: Alan Stern Subject: Re: Power management for SCSI Date: Wed, 13 Aug 2008 17:21:41 +0200 User-Agent: KMail/1.9.9 Cc: Pavel Machek , kernel list , "Linux-pm mailing list" , James.Bottomley@hansenpartnership.com, teheo@novell.com 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: <200808131721.42721.oneukum@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1713 Lines: 37 Am Mittwoch 13 August 2008 16:59:23 schrieb Alan Stern: > On Wed, 13 Aug 2008, Oliver Neukum wrote: > > > 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. > > Is the USB transport unique in its requirement that all the child > devices must be suspended before the link can be powered down? Maybe All children that are USB must be powered down. We know in fact that most drives don't care that the device is suspended. The problem was drive enclosures that cut power upon suspension losing cached data. > that requirement should be made an explicit property of the transport > or the transport class. > > > In fact in true SCSI busses can be shared. So are we using the correct > > approach? > > This is a good question. Most USB mass-storage devices do not act as a > true SCSI bus, but I believe there are a few non-standard ones that do > -- the USB device really contains a SCSI host and arbitrary SCSI > targets can be attached to it. For the moment, we should be safe > enough using a model in which there are no other initiators on a > USB-type SCSI transport, but it's something to keep in mind. So do we really want to do autosuspend on the device level? Or do we work on hosts and just use the suspend()/resume() support of the sd, sr, ... etc? Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/