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Date:   Mon, 16 Jan 2017 16:12:09 -0600
From:   Dave Gerlach <d-gerlach@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Nishanth Menon <nm@...com>, Keerthy <j-keerthy@...com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Tero Kristo <t-kristo@...com>,
        Sudeep Holla <sudeep.holla@....com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Lokesh Vutla <lokeshvutla@...com>
Subject: Re: [PATCH v3 2/4] dt-bindings: Add TI SCI PM Domains

On 01/13/2017 08:40 PM, Rob Herring wrote:
> On Fri, Jan 13, 2017 at 2:28 PM, Dave Gerlach <d-gerlach@...com> wrote:
>> On 01/13/2017 01:25 PM, Rob Herring wrote:
>>>
>>> On Thu, Jan 12, 2017 at 9:27 AM, Dave Gerlach <d-gerlach@...com> 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@...com> 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@...com>
>>>>>>>> Signed-off-by: Dave Gerlach <d-gerlach@...com>
>>>>>>>> ---
>>>>>>>> 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.
>>
>>
>> Yes, ti,sci-id is a new binding. I am referring to the current meaning of
>> the "power-domains" binding, which is where you are asking this property to
>> be added, in "power-domains" cells. This is documented here [1] in the
>> kernel, although looking at it I must admit it is not very clear.
>>
>> The power-domains cell represents an offset into an array of power domains,
>> if you choose to use it. That's what the genpd framework is hard coded to
>> interpret it as. This is correct, as it is an index into a static list of
>> power domains, used to identify which power domain a device belongs to,
>> which is exactly what the genpd framework itself is concerned with. This is
>> already how it is used in the kernel today.
>
> Strictly speaking, the cells are purely for the interpretation of the
> phandle they are associated with. If some controller wants to have 20
> cells, then it could assuming a good reason. The reality is we tend to
> align the meaning of the cells. If genpd is interpreting the cells and
> not letting the driver for the power domain controller interpret them,
> then still, genpd needs to be fixed.

Ok, perhaps the genpd folks on the thread can jump in here with any 
thoughts that they have.

>
> IIRC, initially it was said genpd required 0 cells, hence my confusion.
>
>> My ti,sci-id is not an index into a list of power domains, so it should not
>> go in the power-domains cells and go against what the power-domains binding
>> says that the cell expects. We have one single power domain, and the new
>> ti,sci-id binding is not something the genpd framework itself is concerned
>> with as it's our property to identify a device inside a power domain, not to
>> identify which power domain it is associated with.
>
> What is the id used for? I can understand why you need to know what
> power domain a device is in (as power-domains identifies), but not
> what devices are in a power domain.

We have a system control processor that provides power management 
services to the OS and it responsible for handling the power state of 
each device. This control happens over a communication interface we have 
called TI SCI (implemented at drivers/firmware/ti-sci.c). The 
communication protocol uses these ids to identify each device within the 
power domain so that the control processor can do what is necessary to 
enable that device.

Regards,
Dave

>
> Rob
>

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