linux-kernel - Re: Changes to sysfs PM layer break userspace

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Date:	Tue, 19 Dec 2006 20:32:51 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org, david-b@...bell.net, gregkh@...e.de
Subject: Re: 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@...f.ucam.org
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