From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Neukum Subject: Re: [linux-pm] Power management for SCSI Date: Thu, 14 Aug 2008 16:08:12 +0200 Message-ID: <200808141608.13431.oneukum@suse.de> References: <200808131821.30564.oneukum@suse.de> <20080814135021.GE2262@elf.ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20080814135021.GE2262@elf.ucw.cz> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Pavel Machek Cc: linux-pm@lists.linux-foundation.org, Alan Stern , James.Bottomley@hansenpartnership.com, Linux-pm mailing list , kernel list , teheo@novell.com List-Id: linux-pm@vger.kernel.org Am Donnerstag 14 August 2008 15:50:21 schrieb Pavel Machek: > On Wed 2008-08-13 18:21:29, Oliver Neukum wrote: > > Am Mittwoch 13 August 2008 17:44:46 schrieb Alan Stern: > > > > 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. > > >=20 > > > You misunderstood my question. =A0Are there SCSI transports other= than > > > USB sharing the requirement that all child devices must be suspen= ded > > > before the link can be powered down? > >=20 > > I dispute that USB in general has this property. Some storage devic= es > > need their caches flushed. USB itself is perfectly happy with autos= uspending > > the storage device (host) without telling the disks (devices) > >=20 > > You could even argue that these storage devices violate the USB spe= c. >=20 > Hmm... but suspended devices have very little power budget, right? >=20 > So unless you have external power supply (2.5" frames generally > don't), you can't really suspend and stay spinned up... >=20 True, but the spec says that no state shall be lost. I don't really argue against flushing the caches. But I cannot that thi= s would demand that we should implement autopsuspend for SCSI. It seems like overengineering to me. Regards Oliver