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    SubjectRe: [GIT PULL] PM updates for 2.6.33


    On Sun, 6 Dec 2009, Rafael J. Wysocki wrote:
    >
    > While the current settings are probably unsafe (like enabling PCI devices
    > to be suspended asynchronously by default if there are not any direct
    > dependences between them), there are provisions to make eveything safe, if
    > we have enough information (which also is needed to put the required logic into
    > the drivers).

    I disagree.

    Think of a situation that we already handle pretty poorly: USB mass
    storage devices over a suspend/resume.

    > The device tree represents a good deal of the dependences
    > between devices and the other dependences may be represented as PM links
    > enforcing specific ordering of the PM callbacks.

    The device tree means nothing at all, because it may need to be entirely
    rebuilt at resume time.

    Optimally, what we _should_ be doing (and aren't) for suspend/resume of
    USB is to just tear down the whole topology and rebuild it and re-connect
    the things like mass storage devices. IOW, there would be no device tree
    to describe the topology, because we're finding it anew. And it's one of
    the things we _would_ want to do asynchronously with other things.

    We don't want to build up some irrelevant PM links and callbacks. We don't
    want to have some completely made-up new infrastructure for something that
    we _already_ want to handle totally differently for init time.

    IOW, I argue very strongly against making up something PM-specific, when
    there really doesn't seem to be much of an advantage. We're much better
    off trying to share the init code than making up something new.

    > I'd say if there's a worry that the same register may be accessed concurrently
    > from two different code paths, there should be some locking in place.

    Yeah. And I wish ACPI didn't exist at all. We don't know.

    And we want to _limit_ our exposure to these things.

    Linus


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