Re: [PATCH v7 0/6] ZPODD patches

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On Saturday, September 22, 2012, Alan Stern wrote:
> On Sat, 22 Sep 2012, Rafael J. Wysocki wrote:
> 
> > > There are sd devices with removable media.
> > 
> > OK.  Does the SCSI layer distinguish them from devices without removable media?
> 
> Yes, it does.  struct scsi_device has a .removable member, and the
> Removable flag is part of the response data to the INQUIRY command
> (which belongs to the primary command set common to all SCSI devices).
> 
> > > > User space has an interface to disable runtime PM of any device and it looks
> > > > like that interface should be sufficient to disable the feature in question.
> > > > Why do you think the new interface is needed?
> > > 
> > > Because this is not equivalent to doing no runtime PM at all. SCSI
> > > now defines some powersaving states which do not involve powering
> > > down and thus losing state.
> > 
> > I see. So the sr's runtime suspend may be useful even without the power-off
> > feature, right?
> 
> Exactly.  Even though the drive itself may not be powered off, by 
> putting it into runtime suspend we gain the ability to suspend the 
> ancestor devices.

OK, so what about using a PM QoS-based approach as described (in general
terms) in this message in the "USB ports power off" thread:

http://marc.info/?l=linux-pm&m=134831537224566&w=4

Rafael
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