Re: [RFC] dynamic device power management proposal

[Pavel Machek <pavel@ucw.cz>]

On Thu 2007-03-22 00:49:51, Dmitry Krivoschekov wrote:
> Amit Kucheria wrote:
> > On 3/21/07, Shaohua Li <shaohua.li@intel.com> wrote:
> >> On Wed, 2007-03-21 at 02:30 +0800, Pavel Machek wrote:
> >
> >>> 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_.
> 
> It some circumstances this policy may increase power consumption
> but not decrease it. Consider the case of repeatable operation,

And what... that happens. Lets not break our design because you can
think of very contrieved corner case.

> something like periodic sound beep, with period of 5s.
> In this case, a driver implementing the policy will periodically
> suspend/resume a number of devices - audio controller, codec, ADC,
> but the operation  itself (suspending/resuming) will consume
> more power than power consumed by these devices in case they
> left running for a 5s. In such a case you may want to change
> the predefined  value or  just  disable the policy.

> Yes, we may just not close a sound device file, but phone
> applications I've seen, do close the file.

Fix the app, then.

								Pavel

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