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

[Rob Herring <robh@kernel.org>]

On Mon, Jan 9, 2017 at 11:57 AM, Dave Gerlach <d-gerlach@ti.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@ti.com>
>>> Signed-off-by: Dave Gerlach <d-gerlach@ti.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.

Rob