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    SubjectRe: [RFC/RFT][PATCH v2 5/7] PM / runtime: Flag to indicate PM sleep transitions in progress
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    Hi Rafael,


    On 2016-09-12 23:25, Rafael J. Wysocki wrote:
    > On Monday, September 12, 2016 04:07:27 PM Lukas Wunner wrote:
    >> On Thu, Sep 08, 2016 at 11:29:48PM +0200, Rafael J. Wysocki wrote:
    >>> Introduce a new flag in struct dev_pm_info, pm_sleep_in_progress, to
    >>> indicate that runtime PM has been disabled because of a PM sleep
    >>> transition in progress.
    >> [...]
    >>> That will allow helpers like pm_runtime_get_sync() to be called
    >>> during system sleep transitions without worrying about possible
    >>> error codes they may return because runtime PM is disabled at
    >>> that point.
    >> I have a suspicion that this patch papers over the direct_complete bug
    >> I reported Sep 10 and that the patch is unnecessary once that bug is
    >> fixed.
    > It doesn't paper over anything, but it may not be necessary anyway.
    >
    >> AFAICS, runtime PM is only disabled in two places during the system
    >> sleep process: In __device_suspend() for devices using direct_complete,
    >> and __device_suspend_late() for all devices.
    >>
    >> In both of these phases (dpm_suspend() and dpm_suspend_late()), the
    >> device tree is walked bottom-up. Since we've reordered consumers to
    >> the back of dpm_list, they will be treated *before* their suppliers.
    >> Thus, runtime PM is disabled on the consumers first, and only later
    >> on the suppliers.
    >>
    >> Then how can it be that runtime PM is already disabled on the supplier?
    > Actually, I think that this was a consequence of a bug in device_reorder_to_tail()
    > that was present in the previous iteration of the patchset (it walked suppliers
    > instead of consumers).
    >
    >> The only scenario I can imagine is that the supplier chose to exercise
    >> direct_complete, thus was pm_runtime_disabled() in the __device_suspend()
    >> phase, and the consumer did *not* choose to exercise direct_complete and
    >> later tried to runtime resume its suppliers and itself.
    >>
    >> I assume this patch is a replacement for Marek's [v2 08/10].
    >> @Marek, does this scenario match with what you witnessed?
    > It is not strictly a replacement for it. The Marek's patch was the
    > reason to post it, but I started to think about this earlier.
    >
    > Some people have complained to me about having to deal with error codes
    > returned by the runtime PM framework during system suspend, so I thought
    > it might be useful to deal with that too.
    >
    > That said it probably is not necessary right now.

    I've tested this patchset without this patch and system sleep with
    device link
    enabled worked fine. However this might be also a consequence of
    enabling runtime
    pm during system sleep since v4.8-rc1.

    It looks that for now this patch can be skipped until a real use case for it
    appears.

    Best regards
    --
    Marek Szyprowski, PhD
    Samsung R&D Institute Poland

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