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SubjectRe: Changes to sysfs PM layer break userspace
On Tue, Dec 19, 2006 at 09:23:05PM +0100, Arjan van de Ven wrote:
> On Tue, 2006-12-19 at 20:08 +0000, Matthew Garrett wrote:
> > I'm not sure. Suspending the chip means you lose things like link beat
> > detection, so it's not something you necessarily want to automatically
> > tie to something like interface status.
>
> right now the "spec" for Linux network drivers assumes that you put the
> NIC into D3 on down, except for cases where Wake-on-Lan is enabled etc.

Really? I can't find any drivers that seem to do this. The only calls to
pci_set_power_state seem to be in the suspend, resume, init and exit
routines.

> > Some chips support more
> > fine-grained power management, so we could do something more sensible in
> > that case - but right now, there doesn't seem to be a lot of driver
> > support for it.
>
> sounds like that's the right approach at least .. not talking to the PCI
> hardware directly from userspace...

I'd certainly agree that that's the right thing to do, but userspace has
a habit of using whatever functionality /is/ available to get to a given
end. The semantics of the device/power/state file were never made
terribly clear, and it did have the desired effect of suspending the
device. Removing it without providing warning or a transition pathway is
a pain.

> I can see the point of having more than just "UP" and "DOWN" as
> interface states; "UP", "DOWN" and "OFF" for example...

Agreed.

--
Matthew Garrett | mjg59@srcf.ucam.org
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