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    SubjectRe: [Update][PATCH 7/8] PM / Domains: System-wide transitions support for generic domains (v3)
    On Thu, 23 Jun 2011, Rafael J. Wysocki wrote:

    > Well, let's say this part of the documentation is slightly outdated.
    > It basically refers to the model in which system suspend is a separate global
    > hardware or firmware operation, so the state of devices may be changed by the
    > BIOS or whatever takes over control in the meantime. In that case the kernel
    > has to ensure that the states of devices are consistent with what it thinks
    > about them and the simplest way to achieve that is to put the devices to
    > full power during resume (and back to low power if that's desirable).
    > However, in the case of the systems this patchset is intended for system
    > suspend is achieved by putting various hardware components into low-power
    > states directly in a coordinated way and the system sleep state effectively
    > follows from the low-power states the hardware components end up in. The
    > system is woken up from this state by an interrupt or another mechanism under
    > the kernel's control. As a result, the kernel never gives control away, so
    > the state of devices after the resume is precisely known to it.
    > In consequence, it need not ensure that the state of devices is consistent with
    > its view, because it knows that this is the case. :-)

    That's true for system suspend, but it's probably not true for
    hibernation, even in embedded systems. Of course, many embedded
    systems don't use hibernation at all -- but those that do should be
    aware of this issue.

    > So the documentation should be updated to say what hardware model it is
    > referring to.

    It might be worthwhile to include a little warning about the difference
    between suspend and hibernate.

    Alan Stern

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