[Ksummit-discuss] [TECH TOPIC] PM dependencies

[Shuah Khan]

On Thu, May 15, 2014 at 5:43 PM, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
> On Tuesday 13 May 2014 08:26:09 Shuah Khan wrote:
>>
>> Can we use pm domains concept to solve the problem? As it exists today, it
>> probably can't support loosely associated devices, however, could it be
>> extended to support handling device groups that don't necessarily share
>> power source and/or clock.
>
> If I understand them properly, power domains model groups of devices that
> share common power handling. I'm not sure how they could be used to model PM
> dependencies between devices. Feel free to prove me wrong though :-)
>
>> I started looking at this as a way to solve media device PM issues,
>> however I haven't had a chance to experiment with this idea.

Right now, PM domains currently support grouping of devices that share
power source. What if we extended PM domains to support a concept of
logical grouping of devices that have PM dependencies with a way to
specify dependency ordering?

For example, a media usb device example:
The main driver could create a logical power domain and rest of the
drivers add their devices to the same domain specifying their
dependencies. logical power domain pm handlers can handle ordering. In
some cases, there is a need to save and restore state of tuner i2c and
the existing save_state and restore_state could be used to within the
scope of this logical domain.

I think PM domains can definitely be used for media device case, but I
am not sure about the specific case you are looking at where there is
a clearly identified master driver/device.

These are at the moment ideas and I need to do some work to test these
theories. :)

-- Shuah