Re: [PATCH v2 5/8] dt/bindings: Update binding for PM domain idle states

[Lina Iyer <lina.iyer@linaro.org>]

On Mon, Oct 10 2016 at 11:13 -0600, Sudeep Holla wrote:
>
>
>On 10/10/16 17:43, Lina Iyer wrote:
>>On Mon, Oct 10 2016 at 09:45 -0600, Sudeep Holla wrote:
>>>
>>>
>>>On 07/10/16 23:36, Lina Iyer wrote:
>>>>Update DT bindings to describe idle states of PM domains.
>>>>
>>>>This patch is based on the original patch by Marc Titinger.
>>>>
>>>>Cc: <devicetree@vger.kernel.org>
>>>>Signed-off-by: Marc Titinger <mtitinger+renesas@baylibre.com>
>>>>Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>>>>Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
>>>>Acked-by: Rob Herring <robh@kernel.org>
>>>>---
>>>>.../devicetree/bindings/power/power_domain.txt     | 38
>>>>++++++++++++++++++++++
>>>>1 file changed, 38 insertions(+)
>>>>
>>>>diff --git a/Documentation/devicetree/bindings/power/power_domain.txt
>>>>b/Documentation/devicetree/bindings/power/power_domain.txt
>>>>index 025b5e7..7f8f27e 100644
>>>>--- a/Documentation/devicetree/bindings/power/power_domain.txt
>>>>+++ b/Documentation/devicetree/bindings/power/power_domain.txt
>>>>@@ -29,6 +29,10 @@ Optional properties:
>>>>   specified by this binding. More details about power domain
>>>>specifier are
>>>>   available in the next section.
>>>>
>>>>+- domain-idle-states : A phandle of an idle-state that shall be
>>>>soaked into a
>>>>+                generic domain power state. The idle state
>>>>definitions are
>>>>+                compatible with arm,idle-state specified in [1].
>>>>+
>>>
>>>Please do add the following details to the binding. IMO, this binding is
>>>not complete in terms of specification as there are few open questions:
>>>
>>>1. What not define a standard compatible instead of "arm,idle-state" ?
>>>  I agree it can be used, but as part of this *generic* binding, IMO
>>>  it's better to have something generic and can be used by devices.
>>>  Otherwise, this binding becomes CPU specific, that too ARM CPU
>>>  specific.
>>>
>>We had gone down this path of having a separate DT bindings for domains
>>that is not arm,idle-state. See RFC patches. But the binding did closely
>>match this and it so was suggested that we use arm,idle-state which is
>>already defined.
>>
>
>Either we say this binding is ARM CPU specific or generic, I can't
>understand this mix 'n' match really. You have removed all the CPUIdle
>stuff from this series which is good and makes it simpler, but linking
>it to only "arm,idle-state" make be feel it's not generic. OK I will
>have a look at the RFC as why generic compatible was rejected.
>
I will look for the discussion around it as well. A initial look through
didn't get me the thread I was looking for.

>>>2. Now taking CPU as a special device, how does this co-exist with the
>>>  cpu-idle-states ? Better to have some description may be in the ARM
>>>  CPU idle binding document(not here of-course)
>>>
>>The is a binding for a generic PM domain. This has no bearing on the CPU
>>or its idle states. Its just that the data is compatible with
>>arm,idle-state.
>>
>
>I understand that but it's not that simple which I assume you *do*
>agree. Hence may need bit of an explanation in the binding(not here
>of-course as I mentioned earlier, but in the CPU Idle bindings).
>Please consider DT bindings as any other specification. All I am
>asking is more description in the binding.
>
Any ideas of what description you would like to see? It seemed fairly
explanatory in the idle-states.txt, so I didn't go into depth here.

>>>3. I still haven't seen any explanation for not considering complete
>>>  hierarchical power domain representation which was raised in earlier
>>>  versions. I had provided example for the proposal. I just saw them
>>>  already in use in the upstream kernel by Renasas. e.g.:
>>>  arch/arm/boot/dts/r8a73a4.dtsi
>>>
>>Hierarchical power domains have been available for few years in DT. The
>>OF features of domains have always supported it. Platforms are free to
>>define domains in hierarchy they seem fit for their SoCs. This is a
>>feature that is available today and is not being modified in these
>>patches. It will be creating confusion if I talk about hierarchical
>>domains which are obvious and irrelevant to this series.
>>
>
>Agreed and sorry if I created any confusion. But this binding doesn't
>clearly state how to build up the hierarchy if the leaf node is not a
>power-domain node and I am just trying have those clarifications in the
>binding. It would be good if those details are *explicitly* mentioned in
>the binding, not this particularly, but in CPU Idle one when you
>introduce the user of that.
>
As we have today, devices have their own way of figuring out their idle
states, they are not represented in DT (CPU being an exception). 

>>>  How does that fit with your proposal, though you have not made one
>>>  yet for CPUs in this binding ? In the above file, CPUs have either
>>>  own power domain inside the L2 one which is cluster level power
>>>  domain.
>>>
>>Again, this series is not about the CPUs. This is about adding features
>>to genpd that may be used in other contexts including cpuidle in the
>>future.
>>
>
>Yes I understand and hence I was confused as why I don't see an
>*generic* compatible but just *arm,idle-states* in the example.
>
>>>One must be able to get answers to these above questions with this
>>>binding. Until then it's *incomplete* though it may be correct.
>>>
>>I have always tried to answer all your questions. If anything remains
>>unclarified pls. bring it up.
>>
>
>It's not about questions, and definitely you have answered all my
>questions, no argument there at all. Now we need to make those useful
>discussions part of this binding so that it's *self explanatory* and
>one need not refer back these discussions when writing DT for some
>different SoC which differs from this. Again that could be part of
>your CPUIdle series, I just raised it here as it got mixed sense from
>this series. It was hard to be not to associate CPUIdle for reasons
>mentioned above.
>

Thanks,
Lina