On Wed, 7 Nov 2012, Rafael J. Wysocki wrote:

quoted

Right.  The reasoning behind my proposal goes like this: When there's
no driver, the subsystem can let userspace directly control the
device's power level through the power/control attribute.

Well, we might as well just leave the runtime PM of PCI devices enabled, even
if they have no drivers, but modify the PCI bus type's runtime PM callbacks
to ignore devices with no drivers.

IIRC the reason why we decided to disable runtime PM for PCI device with no
drivers was that some of them refused to work again after being put by the
core into D3.  By making the PCI bus type's runtime PM callbacks ignore them
we'd avoid this problem without modifying the core's behavior.

It comes down to a question of the parent.  If a driverless PCI device
isn't being used, shouldn't its parent be allowed to go into runtime
suspend?  As things stand now, we do allow it.

The problem is that we don't disallow it when the driverless device
_is_ being used.

Alan Stern