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

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 [off-list ref] wrote:

[...]

quoted

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.