Re: REQ_PM vs REQ_TYPE_PM_RESUME

[Phillip Susi <psusi@ubuntu.com>]

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On 1/7/2014 2:49 AM, Aaron Lu wrote:
> We can modify the device's system resume callback. To better
> illustrate the idea, I just made two patches to do this and I did
> some quick tests and didn't find anything wrong.

That misses one key aspect I was trying to capture: it always leaves
the disk runtime suspended after a resume.  If the disk spins up on
its own, as most ata disks do, then the runtime status doesn't
correctly reflect the actual state of the disk.  This means that
applications that delay activities due to the runtime pm status to
avoid waking a disk won't run, and any runtime autosuspend won't kick
in to actually put the disk back to sleep.

To do that, you need to be able to issue a REQUEST SENSE and
conditionally resume the device.  Of course, you can't do that unless
you first get it into a transitional state, but you can't just request
a resume and then conditionally fail it.


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