[PATCH v5 02/16] dt/bindings: Update binding for PM domain idle states

[sudeep.holla@arm.com (Sudeep Holla)]

Hi Kevin,

Thanks for looking at this and simplifying various discussions we had so
far. I was thinking of summarizing something very similar. I couldn't
due to lack of time.

On 16/09/16 18:13, Kevin Hilman wrote:

[...]

> I think we're having some terminology issues...
>
> FWIW, the kernel terminolgy is actually "PM domain", not power domain.
> This was intentional because the goal of the PM domain was to group
> devices that some PM features.  To be very specific to the kernel, they
> us the same set of PM callbacks.  Today, this is most commonly used to
> model power domains, where a group of devices share a power rail, but it
> does not need to be limited to that.
>

Agreed/Understood.

> That being said, I'm having a hard time understanding the root of the
> disagreement.
>

Yes. I tried to convey the same earlier, but have failed. The only
disagreement is about a small part of this DT bindings. We would like to
make it completely hierarchical up to CPU nodes. More comments on that
below.

> It seems that you and Sudeep would like to use domain-idle-states to
> replace/superceed cpu-idle-states with the primary goal (and benefit)
> being that it simplifies the DT bindings.  Is that correct?
>

Correct, we want to deprecate cpu-idle-states with the introduction of
this hierarchical PM bindings. Yes IMO, it simplifies things and avoids
any ABI break we might trigger if we miss to consider some use-case now.

> The objections have come in because that means that implies that CPUs
> become their own domains, which may not be the case in hardware in the
> sense that they share a power rail.
>

Agreed.

> However, IMO, thinking of a CPU as it's own "PM domain" may make some
> sense based on the terminology above.
>

Thanks for that, we do understand that it may not be 100% correct when
we strictly considers hardware terminologies instead of above ones.
As along as we see no issues with the above terminologies it should be fine.

> I think the other objection may be that using a genpd to model domain
> with only a single device in it may be overkill, and I agree with that.

I too agree with that. Just because we represent that in DT in that way
doesn't mean we need to create a genpd to model domain. We can always
skip that if not required. That's pure implementation specifics and I
have tried to convey the same in my previous emails. I must say you have
summarized it very clearly in this email. Thanks again for that.

> But, I'm not sure if making CPUs use domain-idle-states implies that
> they necessarily have to use genpd is what you are proposing.  Maybe
> someone could clarify that?
>

No, I have not proposing anything around implementation in the whole
discussion so far. I have constrained myself just to DT bindings so far.
That's the main reason why I was opposed to mentions of OS vs platform
co-ordinated modes of CPU suspend in this discussion. IMO that's
completely out of scope of this DT binding we are defining here.

Hope that helps/clarifies the misunderstanding/disagreement.

-- 
Regards,
Sudeep