Re: Runtime device power management in userspace

[Pavel Machek <pavel@suse.cz>]

On Út 27-12-05 11:29:56, Patrick Mochel wrote:
> On Tue, Dec 27, 2005 at 08:22:54PM +0100, Pavel Machek wrote:
> 
> > I don't really think we want complexity of putting PCI device into
> > D0/D1/D2/D3hot/D3cold. All that userspace should care about is device
> > working/device suspended, and we could not test all 5 states, anyway.
> 
> What do you mean? 
> 
> The devices and drivers should support various states, and that's the
> whole point of having multiple states - to make a choice based on the
> power saving required vs. the latency requirements of bringing it back.
> 
> Granted, for most things, the latency to return from D3 (hot only, cold
> is irrelevant during runtime) is not going to be noticable, so that's
> probably the only state most devices will ever enter. 

Exactly. And for these "most devices", having to test/debug/support
D1/D2 is not worth the effort.

> But, in some cases, peple are going to care about the intermediate
> states, and we'll need to support them. It's simple enought to know
> what states a PCI device supports, so I don't understand where the
> complexity comes in.. ?

Someone has to test all that... Unless we have in-tree driver that
wants use intermediate states, I think supporting them is bad idea.

								Pavel
-- 
Thanks, Sharp!