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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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