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

[Dave Gerlach <d-gerlach@ti.com>]

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.

 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.

Regards,
Dave

[1] https://patchwork.kernel.org/patch/9385371/

>
> Rob
>