Re: [RFC] dynamic device power management proposal

[Shaohua Li <shaohua.li@intel.com>]

On Mon, 2007-03-19 at 23:44 +0800, Alan Stern wrote:
> On Mon, 19 Mar 2007, Shaohua Li wrote:
> 
> > Runtime device power management or dynamic device power management
> > (dpm).
> >
> > Why dpm:
> >      1. put an idle device into low power state to save power
> >      2. speed up S3/S4. In resume time, we could resume devices only
> as
> >         the devices are used. In suspend time, we could skip
> suspended
> >         devices. (suspend/resume a device equals to change device
> state)
> >
> > Basically we need device driver support, a kernel framework and a
> policy
> > (determine when to change a device’s power state).
> 
> A lot of development along these lines has already been going on in
> the
> USB subsystem.  It isn't complete yet, but a lot of the ideas you
> raise
> have already been implemented.
Ok, I'll look at the USB implementation. On the other hand, I think
there should be a generic framework for all bus types.

> >      4. policy position. The idea is policy resides on userspace.
> Dpm
> >         framework exports device’s busy timestamp, state info,
> >         dependence setting to userspace. According to the info,
> policy
> >         suspends a device in specific time. Resuming a device is
> >         directly done by dpm framework in kernel.
> 
> In USB, we export the idle-time delay value (device is autosuspended
> when it has been idle longer than this) and an administrative
> power-level
> atttribute: on, auto, or suspend.  When set to "on" the device will
> not
> autosuspend; when set to "auto" the device will autosuspend and
> autoresume
> according to the delay setting; when set to "suspend" the device will
> be
> suspended and will not autoresume.
Doing suspend in the driver level isn't flexible. See in the case 'close
console if keyboard/mouse hasn't input', it's hard to do in a driver.

Thanks,
Shaohua
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