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    SubjectRe: Put unused PCI devices in D3
    On Mon, Sep 29, 2008 at 01:11:03PM -0700, Jeffrey W. Baker wrote:

    > Currently it looks to me from browsing the code that D3 is only used in
    > Linux when the whole machine is headed for S3, and the drivers are asked
    > to suspend. I think the drivers should be able to enter D3 in other
    > circumstances:
    > * During pci_unregister_driver ... i.e. on module unload

    The fact that Linux isn't using a device doesn't inherently mean that
    the system isn't using it. For example, the smbus controller will
    probably still be used by ACPI even if there's no Linux driver loaded.

    > * When a network interface is downed

    Yes. Drivers are moving towards this model.

    > * If the device is a bridge or hub with no downstream device

    Potential problems with hotplugging? But sure, this kind of thing is
    being implemented in USB and SCSI.

    > * Whenever userspace requests D3 via sysfs

    This functionality was explicitly removed a few years back.

    > So, what fundamental problem prevents me from, for example, calling
    > pci_set_power_state() from ohci1394's __exit?

    Nothing I'm aware of. It sounds pretty safe in that case. But that would
    require you to load and unload the driver - better to have the driver
    loaded the entire time and make sure it does as much runtime power
    management as possible. I don't know enough about the firewire OHCI
    hardware, but can you power down most of the chip and still get hotplug
    Matthew Garrett |

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