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SubjectRe: [RFC PATCH 2/6] ACPI: Reference devices in ACPI Power Resource
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On Tue, 2012-02-21 at 11:06 -0500, Alan Stern wrote:
> On Tue, 21 Feb 2012, Lin Ming wrote:
>
> > > Then maybe you can use pm_runtime_no_callbacks() for the ZPODD device.
> > > It's explained in Documentation/power/runtime_pm.txt, and I use it for
> > > USB interfaces.
> >
> > If pm_runtime_no_callbacks() is used, runtime PM sysfs attributes
> > won't be created.
> > Then how to disable ZPODD feature in userspace?
> >
> > Currently, I use "control" file of scsi device to enable/disable
> > ZPODD, for example
> > echo auto > /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/power/control
> > echo on > /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/power/control
>
> You could get the same result by using the "control" file for the ATA
> port.
>
> > > The idea is that the ZPODD will never receive any runtime PM callbacks
> > > from the PM core. �Instead the ATA port callback routines will be
> > > responsible for power management of the ZPODD device.
> >
> > Does the ATA port callback also responsible to resume its child?
> >
> > For example,
> > /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/
> >
> > ata0 is resumed.
> >
> > Then who will be responsible to resume host1, target1:0:0 and 1:0:0:0?
> >
> > Or do you mean that we don't need to resume these devices at all?
> > host1 and target1:0:0 are logical devices, but I think 1:0:0:0 is not.
>
> That's right. It makes no difference whether the host and target
> are resumed or suspended. In fact, you could also call
> pm_runtime_no_callbacks() for them.

But host and target are added in scsi layer. How do we know if they are
"logical device"?

Or do you mean that we can call pm_runtime_no_callbacks() for them
because scsi layer(scsi_pm.c) only implements runtime pm for scsi
device.

Thanks,
Lin Ming

>
> Alan Stern
>


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