Re: [RFC/PATCH] dt: bindings: Define bindings for device idle states

[Brendan Jackman <brendan.jackman@arm.com>]

Hi,

(I know I suggested switching to the other thread but I just want to explain my
reasoning here!)

On Wed, Aug 31, 2016 at 04:19:41PM +0200, Ulf Hansson wrote:
> On 31 August 2016 at 12:16, Brendan Jackman <brendan.jackman@arm.com> wrote:
[...]
> > There was some previous discussion of whether device idle state bindings are
> > necessary. It was proposed that rather than adding a whole new binding, we could
> > just use the power domain idle state binding from [2]. We suggested that any
> > device that has an idle state is, by definition, in a power domain of its own:
> > rather than add a device-idle-states property to that device, we just put it in
> > a power domain with a domain-idle-states property.
>
> Yes, we can do that software wise, but is that really a proper
> description of the HW!?
>

It's probably not what SoC docs would explicitly list under "power domains" but
I think "set of components that are bound by a common power state" is a
reasonable definition for a power domain.

I think (?) your objection is that a device could have idle states that it
controls by itself and does not switch "off", for example in the case of a
device that has an idle state where it gates its clock but does not cut voltage,
or WFI in an ARM CPU. My thinking is: just because the transitions into those
power states isn't triggered by a separate power controller, I don't think that
means no "power domain" exists.

Perhaps that's a glitch in my vocabulary.