Re: [linux-pm] subtle pm_runtime_put_sync race and sdio functions

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On Tue, 21 Dec 2010, Kevin Hilman wrote:

> That being said, another thing we discussed briefly at LPC was wondering
> about reason(s) behind the DPM core locking out runtime PM transitions
> in the first place.

The reason is to prevent confusion from unwanted runtime-PM state 
changes during a system sleep transition.

> Currently runtime PM transitions are blocked in dpm_prepare() and only
> allowed again in dpm_complete().  How about locking out runtime PM
> transitions only until the DPM suspend operation is complete.  IOW,
> rather than waiting for dpm_complete() to re-allow runtime PM
> transitions, what about allowing them after dpm_suspend()?  I haven't
> actually tested this yet, since I'm busy with getting OMAP PM stuff
> ready for the merge window, so it's just and idea so far.  Of course
> similar will be needed to block runtime PM transitions during
> dpm_resume().  

That would defeat the purpose.  We need to prevent unwanted state
changes during the entire sleep transition, not just during the time 
that dpm_suspend is running.

Alan Stern

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