Re: REQ_PM vs REQ_TYPE_PM_RESUME

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On Wed, 8 Jan 2014, Alan Stern wrote:

> In essence, you want your disk's state to move directly from unpowered
> (system asleep) to runtime-suspended with no intermediate active -- but
> only if the disk doesn't spin up all by itself.

> In the end, it sounds like what you want can be done fairly easily.  

It turns out there is a snag.  The PM core is set up such that during
system sleep transitions, there's no way to tell whether or not
userspace has permitted runtime PM for a device.  (This is because the
core wants to prevent untimely runtime suspends from occurring in the
middle of a system sleep transition, and to do so it uses the same
mechanism as it does when userspace disallows runtime suspend.)

As a result, we must not go directly from unpowered to
runtime-suspended.  Not without some sort of change to the PM core.

Alan Stern

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