Re: [RFC] dynamic device power management proposal

[Pavel Machek <pavel@ucw.cz>]

Hi!

> | > > No, that's not how it works; look at hda_audio, it already has
> | > > powersave. Just power down audio card 5 seconds after its control file
> | > > is closed.
> | > It's another case of doing policy in a driver.
> | >
> | 
> | IMHO, this kind of policy is best handled inside the driver because it
> | is specific to the hardware. This will ensure that the driver will
> | just work on every distro without some userspace policy being present
> | and setup _correctly_.
> ---
> 
> On an embedded device, the knowledge of when it makes sense to keep a
> disk spinning, to avoid latency when it's needed next, versus when it
> makes sense to spin it down to save power, probably fits better in user
> space than in the kernel. In such a case there's likely to be a "master"
> application (in our case, for instance, "the phone application") that
> owns a lot of knowledge about whole-system state and user interactions.
> Not, of course, that we have a disk to spin down.

Agreed. Please use existing interfaces. Patch to spin disk down and
keep it down is available... but hdparm -y is enough for you.

> On the other hand, we also have devices that do their own power saving,
> largely in cases where they don't have latency issues large enough to
> worry about.

Yep. 

And we do not need great new handwavy framework for
this... please. Just add support for platform you care about.
								Pavel
-- 
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