On Mon, 28 Jun 2004, Oliver Neukum wrote:
> > > Then we must refuse any sleep states that want to power down the bus.
> >
> > No, if the bus powers off the call sequence seen by that driver
> > will be suspend()->disconnect() rather than suspend()->resume().
>
> This will do horrible things if the attached device has considerable state.
> With usb-storage it will lead to data loss.
What sort of data loss are you referring to?
Data in filesystem buffers not yet flushed to the device?
Such data are lost whenever a device is disconnected before
unmounting, no matter whether it is suspended first.
Data in the device buffers not yet written to the medium?
If it is written properly, the high-level SCSI driver
will tell the device to flush its caches when the suspend
notification arrives.
Maybe the problem here is one of semantics. It seems to me that the only
way to make power-off suspend work is if it is a whole-system suspend.
In such situations filesystem data could be fully flushed and other sorts
of preventative action taken. But suspending a single device by removing
its power isn't a suspend at all -- it's a disconnect.
Alan Stern
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