Re: [PATCH v3 2/4] dt-bindings: Add TI SCI PM Domains

[Rob Herring]

On Thu, Jan 12, 2017 at 9:27 AM, Dave Gerlach <d-gerlach@xxxxxx> wrote:
> Rob,
>
> On 01/11/2017 03:34 PM, Rob Herring wrote:
>>
>> On Mon, Jan 9, 2017 at 11:57 AM, Dave Gerlach <d-gerlach@xxxxxx> wrote:
>>>
>>> Rob,
>>>
>>> On 01/09/2017 11:50 AM, Rob Herring wrote:
>>>>
>>>>
>>>> On Wed, Jan 04, 2017 at 02:55:34PM -0600, Dave Gerlach wrote:
>>>>>
>>>>>
>>>>> Add a generic power domain implementation, TI SCI PM Domains, that
>>>>> will hook into the genpd framework and allow the TI SCI protocol to
>>>>> control device power states.
>>>>>
>>>>> Also, provide macros representing each device index as understood
>>>>> by TI SCI to be used in the device node power-domain references.
>>>>> These are identifiers for the K2G devices managed by the PMMC.
>>>>>
>>>>> Signed-off-by: Nishanth Menon <nm@xxxxxx>
>>>>> Signed-off-by: Dave Gerlach <d-gerlach@xxxxxx>
>>>>> ---
>>>>> v2->v3:
>>>>>         Update k2g_pds node docs to show it should be a child of pmmc
>>>>> node.
>>>>>         In early versions a phandle was used to point to pmmc and docs
>>>>> still
>>>>>         incorrectly showed this.
>>>>>
>>>>>  .../devicetree/bindings/soc/ti/sci-pm-domain.txt   | 59 ++++++++++++++
>>>>>  MAINTAINERS                                        |  2 +
>>>>>  include/dt-bindings/genpd/k2g.h                    | 90
>>>>> ++++++++++++++++++++++
>>>>>  3 files changed, 151 insertions(+)
>>>>>  create mode 100644
>>>>> Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>  create mode 100644 include/dt-bindings/genpd/k2g.h
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>> b/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>> new file mode 100644
>>>>> index 000000000000..4c9064e512cb
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>> @@ -0,0 +1,59 @@
>>>>> +Texas Instruments TI-SCI Generic Power Domain
>>>>> +---------------------------------------------
>>>>> +
>>>>> +Some TI SoCs contain a system controller (like the PMMC, etc...) that
>>>>> is
>>>>> +responsible for controlling the state of the IPs that are present.
>>>>> +Communication between the host processor running an OS and the system
>>>>> +controller happens through a protocol known as TI-SCI [1]. This pm
>>>>> domain
>>>>> +implementation plugs into the generic pm domain framework and makes
>>>>> use
>>>>> of
>>>>> +the TI SCI protocol power on and off each device when needed.
>>>>> +
>>>>> +[1] Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
>>>>> +
>>>>> +PM Domain Node
>>>>> +==============
>>>>> +The PM domain node represents the global PM domain managed by the
>>>>> PMMC,
>>>>> +which in this case is the single implementation as documented by the
>>>>> generic
>>>>> +PM domain bindings in
>>>>> Documentation/devicetree/bindings/power/power_domain.txt.
>>>>> +Because this relies on the TI SCI protocol to communicate with the
>>>>> PMMC
>>>>> it
>>>>> +must be a child of the pmmc node.
>>>>> +
>>>>> +Required Properties:
>>>>> +--------------------
>>>>> +- compatible: should be "ti,sci-pm-domain"
>>>>> +- #power-domain-cells: Must be 0.
>>>>> +
>>>>> +Example (K2G):
>>>>> +-------------
>>>>> +       pmmc: pmmc {
>>>>> +               compatible = "ti,k2g-sci";
>>>>> +               ...
>>>>> +
>>>>> +               k2g_pds: k2g_pds {
>>>>> +                       compatible = "ti,sci-pm-domain";
>>>>> +                       #power-domain-cells = <0>;
>>>>> +               };
>>>>> +       };
>>>>> +
>>>>> +PM Domain Consumers
>>>>> +===================
>>>>> +Hardware blocks that require SCI control over their state must provide
>>>>> +a reference to the sci-pm-domain they are part of and a unique device
>>>>> +specific ID that identifies the device.
>>>>> +
>>>>> +Required Properties:
>>>>> +--------------------
>>>>> +- power-domains: phandle pointing to the corresponding PM domain node.
>>>>> +- ti,sci-id: index representing the device id to be passed oevr SCI to
>>>>> +            be used for device control.
>>>>
>>>>
>>>>
>>>> As I've already stated before, this goes in power-domain cells. When you
>>>> have a single thing (i.e. node) that controls multiple things, then you
>>>> you need to specify the ID for each of them in phandle args. This is how
>>>> irqs, gpio, clocks, *everything* in DT works.
>>>
>>>
>>>
>>> You think the reasoning for doing it this way provided by both Ulf and
>>> myself on v2 [1] is not valid then?
>>>
>>> From Ulf:
>>>
>>> To me, the TI SCI ID, is similar to a "conid" for any another "device
>>> resource" (like clock, pinctrl, regulator etc) which we can describe
>>> in DT and assign to a device node. The only difference here, is that
>>> we don't have common API to fetch the resource (like clk_get(),
>>> regulator_get()), but instead we fetches the device's resource from
>>> SoC specific code, via genpd's device ->attach() callback.
>>
>>
>> Sorry, but that sounds like a kernel problem to me and has nothing to
>> do with DT bindings.
>>
>>> From me:
>>>
>>> Yes, you've pretty much hit it on the head. It is not an index into a
>>> list
>>> of genpds but rather identifies the device *within* a single genpd. It is
>>> a
>>> property specific to each device that resides in a ti-sci-genpd, not a
>>> mapping describing which genpd the device belongs to. The generic power
>>> domain binding is concerned with mapping the device to a specific genpd,
>>> which is does fine for us, but we have a sub mapping for devices that
>>> exist
>>> inside a genpd which, we must describe as well, hence the ti,sci-id.
>>>
>>>
>>> So to summarize, the genpd framework does interpret the phandle arg as an
>>> index into multiple genpds, just as you've said other frameworks do, but
>>> this is not what I am trying to do, we have multiple devices within this
>>> *single* genpd, hence the need for the ti,sci-id property.
>>
>>
>> Fix the genpd framework rather than work around it in DT.
>
>
> I still disagree that this has nothing to do with DT bindings, as the
> current DT binding represents something different already. I am trying to
> extend it to give me additional information needed for our platforms. Are
> you saying that we should break what the current DT binding already
> represents to mean something else?

No idea because what's the current binding? From the patch, looks like
a new binding to me.

Rob