Re: [PATCH v7 0/6] ZPODD patches

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Saturday, September 22, 2012, Oliver Neukum wrote:
> On Friday 21 September 2012 23:18:27 Rafael J. Wysocki wrote:
> 
> > Now, James says he doesn't like the way ready_to_power_off is used.  Sure
> > enough, it is totally irrelevant to the majority of SCSI devices.  It actually
> > is totally irrelevant to everything in the SCSI subsystem except for the sr
> > driver and libata.  So I wonder if you have considered any alternative
> > way to address the use case at hand?
> 
> Strictly speaking, USB on very modern systems could use it, but doesn't
> in the current implementation.

OK

Still, why does the flag have to be in struct scsi_device for this purpose?

> > That sounds reasonable enough, but the role of the powered_off and
> > need_eject flags could be explained a bit better.  In particular, it would
> 
> I think need_eject needs to be renamed. Something like "media_change_detected"
> 
> > be nice to have explained why they have to be present in struct scsi_device,
> > because they don't seem to be particularly useful for many SCSI devices
> > that aren't CD drives (the need_eject one in particular).
> 
> There are sd devices with removable media.

OK.  Does the SCSI layer distinguish them from devices without removable media?

> > 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?

Rafael