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    SubjectRe: [linux-pm] [patch] pm: fix runtime powermanagement's /sys interface
    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!
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