Oliver Neukum wrote:
Am Mittwoch, 22. September 2004 17:15 schrieb Alan Stern:
This leaves some unanswered questions. On some buses (such as PCI or
USB), it's not possible to access a device whenever its state is higher
than 0.
Not quite true. PCI config space access is allowed, which is how
things move from D1 to D2, or D2 to D3hot, etc. And I suppose it'd
make sense that CardBus, PCI Hotplug, and similar variants be able
to "enter" D3cold ... e.g. by powering off the slot then removing the
device. That's the same thing USB can do with suspended devices:
power off the hub port.
So how can a driver increase the state, once it is positive?
As shown above ... this is not an issue.
Conceivably this could cause a system-wide state-3 suspend to fail if some
device were already say in state 1.
Worse, it applies to any device higher up in the tree.
The transition rule that you can enter a state >0 only from 0
and only 0 from a state >0 is IMHO needed.
Neither for USB nor PCI is such a rule needed.
- Dave
Regards
Oliver
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