Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757944AbYHMThl (ORCPT ); Wed, 13 Aug 2008 15:37:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754808AbYHMThX (ORCPT ); Wed, 13 Aug 2008 15:37:23 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:33292 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754007AbYHMThW (ORCPT ); Wed, 13 Aug 2008 15:37:22 -0400 Date: Wed, 13 Aug 2008 15:37:21 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: Stefan Richter , Pavel Machek , kernel list , Linux-pm mailing list , , Subject: Re: Power management for SCSI In-Reply-To: <200808131825.27303.oneukum@suse.de> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1732 Lines: 40 On Wed, 13 Aug 2008, Oliver Neukum wrote: > > In Alan's patch, SCSI calls scsi_host_template methods (if the LLD > > provides ones) to suspend and resume a Scsi_Host. The LLD can use them > > to work with the underlying infrastructure to determine what can be done > > at that time. I.e. are there other protocols or other initiator-like > > nodes sharing the link? If yes or if "maybe yes", the infrastructure > > keeps the link up. If not, it can move it into a low-power state. > > That is a parculiar way of viewing it. Alan's patch introduce runtime > pm attributes to the devices. Quoting: > > > +/** > + * scsi_suspend_sdev - suspend a SCSI device > + * @sdev: the scsi_device to suspend > + * @msg: Power Management message describing this state transition > + * > + * SCSI devices can't actually be suspended in a literal sense, > + * because SCSI doesn't have any notion of power management. Instead > + * this routine drains the request queue and calls the ULD's suspend > + * method to flush caches, spin-down drives, and so on. > + * > + * If the suspend succeeds, we call scsi_autosuspend_host to decrement > + * the host's count of unsuspended devices and invoke the LLD's suspend > + * method. > > So you cannot operate on the link independent from the devices. With the original patch, you can't operate on the link independent from the devices. But with the revised patch (whenever I manage to find time to write it!), you _will_ be able to. Alan Stern -- 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/