Re: [PATCH v2 2/4] dt-bindings: Add TI SCI PM Domains

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

Rob, Ulf, Jon,
On 10/27/2016 08:15 AM, Dave Gerlach wrote:
> +Jon
> On 10/26/2016 04:59 PM, Rob Herring wrote:
>> On Mon, Oct 24, 2016 at 12:00 PM, Kevin Hilman <khilman@baylibre.com> wrote:
>>> Dave Gerlach <d-gerlach@ti.com> writes:
>>>
>>>> Hi,
>>>> On 10/21/2016 01:48 PM, Kevin Hilman wrote:
>>>>> Dave Gerlach <d-gerlach@ti.com> writes:
>>>>>
>>>>>> 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>
>>>>>> ---
>>>>>>  .../devicetree/bindings/soc/ti/sci-pm-domain.txt   | 54 +++++++++++++
>>>>>>  MAINTAINERS                                        |  2 +
>>>>>>  include/dt-bindings/genpd/k2g.h                    | 90 ++++++++++++++++++++++
>>>>>>  3 files changed, 146 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..32f38a349656
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt
>>>>>> @@ -0,0 +1,54 @@
>>>>>> +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.
>>>>>> +
>>>>>> +Required Properties:
>>>>>> +--------------------
>>>>>> +- compatible: should be "ti,sci-pm-domain"
>>>>>> +- #power-domain-cells: Must be 0.
>>>>>> +- ti,sci: Phandle to the TI SCI device to use for managing the devices.
>>>>>>
>>>>>> +Example:
>>>>>> +--------------------
>>>>>> +k2g_pds: k2g_pds {
>>>>>
>>>>> should use generic name like "power-contoller", e.g. k2g_pds: power-controller
>>>>
>>>> Ok, that makes more sense.
>>>>
>>>>>
>>>>>> +        compatible = "ti,sci-pm-domain";
>>>>>> +        #power-domain-cells = <0>;
>>>>>> +        ti,sci = <&pmmc>;
>>>>>> +};
>>>>>> +
>>>>>> +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.
>>>>>
>>>>> This ID doesn't look right.
>>>>>
>>>>> Why not use #power-domain-cells = <1> and pass the index in the DT? ...
>>
>> Exactly. ti,sci-id is a NAK for me.
>
> I was told not to use the onecell during v1 discussion. I agree this would be
> ideal but I cannot due to what the bindings represent, the phandle parameter is
> an index into a list of genpds, whereas we need an actual ID number we can use
> and I do not have the ability to get that from the phandle.
>
> @Ulf/Jon, is there any hope of bringing back custom xlate functions for genpd
> providers? I don't have a good background on why it was even removed. I can
> maintain a single genpd for all devices but I need a way to parse this ID,
> whether it's from a separate property or a phandle. It is locked now to indexing
> into a list of genpds but I need additional per device information for devices
> bound to a genpd and I need either a custom parameter or the ability to parse
> the phandle myself.
>

Any comments here? The meaning of the phandle onecell is fixed in the 
genpd framework so I'm not sure how we want to move forward with this, I 
need to pass a power domain ID to the genpd driver, and if this 
shouldn't be a new property I'm not sure what direction we should take.

Regards,
Dave

>>
>>>>>
>>>>>> +See dt-bindings/genpd/k2g.h for the list of valid identifiers for k2g.
>>>>>> +
>>>>>> +Example:
>>>>>> +--------------------
>>>>>> +uart0: serial@02530c00 {
>>>>>> +   compatible = "ns16550a";
>>>>>> +   ...
>>>>>> +   power-domains = <&k2g_pds>;
>>>>>> +   ti,sci-id = <K2G_DEV_UART0>;
>>>>>
>>>>> ... like this:
>>>>>
>>>>>      power-domains = <&k2g_pds K2G_DEV_UART0>;
>>>>
>>>> That's how I did it in version one actually. I was able to define my
>>>> own xlate function to parse the phandle and get that index, but Ulf
>>>> pointed me to this series by Jon Hunter [1] that simplified genpd
>>>> providers and dropped the concept of adding your own xlate. This locks
>>>> the onecell approach to using a fixed static array of genpds that get
>>>> indexed into (without passing the index to the provider, just the
>>>> genpd that's looked up), which doesn't fit our usecase, as we don't
>>>> want a 1 to 1 genpd to device mapping based on the comments provided
>>>> in v1. Now we just use the genpd device attach/detach hooks to parse
>>>> the sci-id and then use it in the genpd device start/stop hooks.
>>
>> I have no idea what any of this means. All sounds like driver
>> architecture, not anything to do with bindings.
>
> This was a response to Kevin, not part of binding description.
>
>>
>>>
>>> Ah, right.  I remember now.  This approach allows you to use a single
>>> genpd as discussed earlier.
>>>
>>> Makes sense now, suggestion retracted.
>>
>> IIRC, the bindings in Jon's case had a node for each domain and didn't
>> need any additional property.
>
> Yes but we only have one domain and index into it, not into a list of domains,
> so the additional property is solving a different problem.
>
> Regards,
> Dave
>
>>
>> Rob
>>
>