[PATCH] SCSI midlayer power management

[Nathan Bryant]

Hi,

This proposed patch implements enough power-management support within 
the SCSI midlayer to get ACPI S3 working on my system. Changes as follows:

* Add generic_scsi_{suspend,resume} methods to scsi.c
* Add suspend and resume callbacks to the scsi_driver structure, and 
implement those callbacks in sd.c
* In sd.c, we call sd_shutdown on suspend, in order to synchronize the 
write-back cache.
* In sd.c, we call sd_rescan from sd_resume in order to ensure that 
drives have spun up and avoid passing not ready errors back to the block 
layer.
* In generic_scsi_suspend, we call scsi_device_quiesce before calling 
the scsi_driver suspend callback. We resume from quiesce state in 
reverse order in generic_scsi_resume.

ACPI S1 and S4/swsusp are untested, but I think there should be no 
regressions with S1. To do S1 properly, we probably need to tell the 
drive to spin down, and I don't know what the SCSI command is for 
that... For S4, the call to scsi_device_quiesce might pose a problem for 
the subsequent state dump to disk. But I'm not sure swsusp ever worked 
for SCSI.

This might help SATA drives, too, but I seem to remember that the SATA 
layer doesn't properly emulate the SYNCHRONIZE_CACHE command.

Comments, anybody? Can this be applied upstream? I think it's a step in 
the right direction.

Applies to scsi-misc-2.6

Nathan
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