Date:   Wed, 26 Oct 2016 16:59:47 -0500
From:   Rob Herring <robh@...nel.org>
To:     Kevin Hilman <khilman@...libre.com>
Cc:     Dave Gerlach <d-gerlach@...com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "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>
Subject: Re: [PATCH v2 2/4] dt-bindings: Add TI SCI PM Domains

On Mon, Oct 24, 2016 at 12:00 PM, Kevin Hilman <khilman@...libre.com> wrote:
> Dave Gerlach <d-gerlach@...com> writes:
>
>> Hi,
>> On 10/21/2016 01:48 PM, Kevin Hilman wrote:
>>> Dave Gerlach <d-gerlach@...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@...com>
>>>> Signed-off-by: Dave Gerlach <d-gerlach@...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.

>>>
>>>> +See dt-bindings/genpd/k2g.h for the list of valid identifiers for k2g.
>>>> +
>>>> +Example:
>>>> +--------------------
>>>> +uart0: serial@...30c00 {
>>>> +   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.

>
> 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.

Rob

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