From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756628Ab1KXQgX (ORCPT ); Thu, 24 Nov 2011 11:36:23 -0500 Received: from netrider.rowland.org ([192.131.102.5]:34056 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754982Ab1KXQgV (ORCPT ); Thu, 24 Nov 2011 11:36:21 -0500 Date: Thu, 24 Nov 2011 11:36:20 -0500 (EST) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Lin Ming cc: "linux-kernel@vger.kernel.org" , "linux-ide@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-pm@vger.kernel.org" , Jeff Garzik , "Rafael J. Wysocki" , James Bottomley , Tejun Heo , "Huang, Ying" , "Zhang, Rui" Subject: Re: [PATCH v3 3/6] [SCSI] runtime resume device before system suspend In-Reply-To: <1322137287.2597.10.camel@hp6530s> 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 On Thu, 24 Nov 2011, Lin Ming wrote: > > The point of this patch is to handle drivers that do different things > > for runtime suspend and system sleep. The only SCSI driver that > > currently supports runtime suspend is sd, and it treats runtime suspend > > the same as system sleep. (Earlier I said it doesn't spin down disks > > for runtime suspend -- that was wrong, it does. It skips the spin-down > > step only for PM_EVENT_FREEZE, which is part of the hibernation > > procedure.) > > > > Until other SCSI drivers support runtime suspend, this patch shouldn't > > be needed. And spinning up runtime-suspended disks could add a lengthy > > delay to the system sleep transition, so it's better not to do this if > > at all possible. > > For sd driver, PMSG_SUSPEND and PMSG_HIBERNATE are compatible with > PMSG_AUTO_SUSPEND. PMSG_FREEZE is not compatible. I'm not sure what you mean. In the sd driver, PMSG_SUSPEND, PMSG_HIBERNATE, and PMSG_AUTO_SUSPEND all do exactly the same thing. PMSG_FREEZE does a little less -- it doesn't spin down the drive. > So we only need to runtime resume sd for PMSG_FREEZE case. No, we don't. PMSG_FREEZE does not care whether the drive is spinning or not. (That's why it skips the spin-down step.) Therefore it's silly to restart a stopped drive just in order to do a PMSG_FREEZE. > How about below? > > diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c > index 549ea72..e2759d9 100644 > --- a/drivers/scsi/scsi_pm.c > +++ b/drivers/scsi/scsi_pm.c > @@ -50,7 +50,13 @@ static int scsi_bus_suspend_common(struct device *dev, pm_message_t msg) > int err = 0; > > if (scsi_is_sdev_device(dev)) { > - pm_runtime_resume(dev); > + if (pm_runtime_suspended(dev)) { > + if (msg.event == PM_EVENT_FREEZE) > + pm_runtime_resume(dev); > + else The 3 lines above aren't needed. > + return 0; > + } > + > err = scsi_dev_type_suspend(dev, msg); > } > return err; Of course, this leaves the patch in pretty much the same state as what Tejun objected to in http://marc.info/?l=linux-ide&m=132136894329965&w=2 I think this email discussion has answered his objection: The only SCSI top-level driver implementing runtime suspend is sd, and sd treats runtime suspend the same as system sleep. It might be a good idea to add a comment with this explanation along with the new code, however. Alan Stern