Re: [patch] pm: fix runtime powermanagement's /sys interface

Pavel Machek
2006-01-07T10:25:54Z

On So 07-01-06 03:36:02, Adam Belay wrote:
> On Wed, Jan 04, 2006 at 10:34:05PM +0100, Pavel Machek wrote:
> > On Út 27-12-05 20:22:04, Patrick Mochel wrote:
> > We want _common_ values, anyway. So, we do not want "D0", "D1", "D2",
> > "D3hot" in PCI cases. We probably want "on", "D1", "D2", "suspend",
> > and I'm not sure about those "D1" and "D2" parts. Userspace should not
> > have to know about details, it will mostly use "on"/"suspend" anyway.
> >
> > > > One day, when we find device that needs it, we may want to add more
> > > > states. I don't know about such device currently.
> > >
> > > There are many devices already do - there are PCI, PCI-X, PCI Express,
> > > ACPI devices, etc that do. But, you simply cannot create a single
> > > decent
> >
> > I asked for an example.
>
> Look at the ACPI spec, it has several examples...
>
> 1.) most sound cards have more than two states. (once again latency over
> power savings trade offs)

What is the latency in typical "most sound card" case?

> 2.) many PCI devices with wake support use different D-levels depending
> on wake settings

...can be done internally in driver.

> 4.) IDE hard drives and other storage media have "sleep", "suspend",
> etc.

Yep; but spindown takes 5 seconds, so if you need to reset ide bus or
not to get it back is driver detail. Plus notice how power consuption
in sleep and suspend is almost same; motor not running is big deal
there. Ouch and hdparm already handles these.

> 5.) SATA controllers have more states than just "on" and "off". Also
> these states are independent of the PCI d-states.

...so "bus provides list of states" ideas do not really work.

> 6.) many video cards implement D1 and D2 as you've already seen. This
> is often more a matter of "we only know how to restore from such and such
> states"

Excatly, so "on"/"off" is enough for them.

> 7.) Many processors support of wealth of different power states

Processors are handled specially, anyway.
Pavel
--
Thanks, Sharp!