suspend/resume is a lot more complicated than just flushing a cache, the below will probably get you safe asleep but you will never get devices alive again after power-up on suspend-to-ram.
I also greatly prefer issuing a standby command to the drive after the flush, so that we don't risk using the emergency parks of the drive. If a drive happens to lie about wrt the flush command, it gets an extra chance to flush the cache as it now knows that power will be gone very soon. So I think the ->suspend/->resume hooks should belong to the LLD, not the ULD as the ULD has no idea how to suspend all devices types.
You are right about issuing the standby command after flush. I don't think an LLD hook is the proper way to accomplish it, however.
The SCSI layer needs to issue the START STOP UNIT command in response to a suspend event, and libata-scsi will (per SAT spec) translate that into the ATA standby command. Merely following the relevant SCSI+SAT+ATA standards gets us there.
Longer term, SATA PM through SCSI will have three facets:
* Device PM. This is best handled by the device class driver (sd/sr/st).
* Bus PM. This is best handled by the transport class driver (need to write for SATA and SAS).
* Host PM. This is handled in the obvious manner, using existing PM driver hooks. PCI D0/D3, etc.
I can describe how this will look when libata is divorced from SCSI, if you would like, too...
Jeff
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