Re: REQ_PM vs REQ_TYPE_PM_RESUME

[Phillip Susi <psusi@ubuntu.com>]

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On 1/8/2014 4:21 PM, Alan Stern wrote:
> I never saw your patches.  Where were they posted?

Higher up in this thread on linux-ide and linux-scsi.  Subject was Let
sleeping disks lie.

> If you issue the REQUEST SENSE command in the usual way (going
> through the SCSI and block layers), and the disk is already in
> runtime suspend, it won't do what you want.  The block layer won't
> deliver requests until the device leaves the RPM_SUSPENDED state.
> In addition, when it receives the command the block layer will
> submit a deferred runtime-resume request, which rather defeats the
> whole purpose.

Right, which is why I left the device in the active state and used the
pre/post_suspend functions to change the queue into the RPM_SUSPENDING
state, then either complete the transition to RPM_SUSPENDED, or bail
out and go back to RPM_ACTIVE.

> What happens with non-ATA disks?

Same thing: they return a sense status that either says they are
suspended, stopped, or normal.


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