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
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