On Mon, 1 Nov 2004, Pavel Machek wrote:
> Hi!
>
> > It might be a good idea to add a generic PM state for devices that are in
> > a low-performance mode but will automatically transfer (or be transferred)
> > back to full-performance when the next request arrives.
> >
> > This came up in working on auto-suspend for the usb-storage driver. When
> > a drive is auto-suspended we definitely do _not_ want to put all the
> > descendant devices into a low-power state first. That would defeat
> > the
>
> Is not this auto-suspend prety much "powered on" state from the view
> of upper layers? It looks to me like upper layers do not need to know
> about this one..
I find it a bit confusing to talk about "upper layers" here; the layers in
question are the SCSI host, SCSI device, general disk, partition,
filesystem, etc. -- and they are all "lower" in the sense of being
farther from the root of the device tree. (This presumes one believes,
like most computer scientists, that trees grow _down_ from their roots!)
In any case, yes, you are right; these layers do not and should not know
about auto-suspend. My reason for bringing it up is because it seems to
contradicts this paragraph from David's recent write-up:
+ Devices generally can't enter low power modes before their children,
or leave them before their parents. At least some of that logic might
need to live in the bridge or hub drivers managing those relationships.
And yes, he wrote "generally", so this is an exception to the rule. It
might end up being a wide-spread exception.
Alan Stern
