From: Alan Stern <stern@rowland.harvard.edu>
To: Lin Ming <ming.m.lin@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Jeff Garzik <jgarzik@pobox.com>,
"Rafael J. Wysocki" <rjw@sisk.pl>,
James Bottomley <JBottomley@parallels.com>,
Tejun Heo <tj@kernel.org>, "Huang, Ying" <ying.huang@intel.com>,
"Zhang, Rui" <rui.zhang@intel.com>
Subject: Re: [PATCH v3 3/6] [SCSI] runtime resume device before system suspend
Date: Thu, 24 Nov 2011 11:36:20 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1111241123030.21532-100000@netrider.rowland.org> (raw)
In-Reply-To: <1322137287.2597.10.camel@hp6530s>
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
next prev parent reply other threads:[~2011-11-24 16:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-23 7:01 [PATCH v3 0/6] ata port runtime power management support Lin Ming
2011-11-23 7:01 ` [PATCH v3 1/6] ata: make ata port as parent device of scsi host Lin Ming
2011-11-23 7:01 ` [PATCH v3 2/6] scsi: add flag to skip the runtime PM calls on the host Lin Ming
2011-11-23 7:01 ` [PATCH v3 3/6] [SCSI] runtime resume device before system suspend Lin Ming
2011-11-23 17:02 ` Alan Stern
2011-11-24 12:21 ` Lin Ming
2011-11-24 16:36 ` Alan Stern [this message]
2011-11-24 19:57 ` Tejun Heo
2011-11-24 22:54 ` Alan Stern
2011-11-24 23:01 ` Tejun Heo
2011-11-25 0:17 ` Alan Stern
2011-11-25 13:50 ` Lin Ming
2011-11-25 15:19 ` Alan Stern
2011-11-23 7:01 ` [PATCH v3 4/6] [SCSI] sd: check runtime status in sd_shutdown Lin Ming
2011-11-23 7:01 ` [PATCH v3 5/6] ata: add ata port system PM callbacks Lin Ming
2011-11-23 7:01 ` [PATCH v3 6/6] ata: add ata port runtime " Lin Ming
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