From: Kevin Hilman <khilman@baylibre.com>
To: Dave Gerlach <d-gerlach@ti.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-pm@vger.kernel.org>, <devicetree@vger.kernel.org>,
        Nishanth Menon <nm@ti.com>, Keerthy <j-keerthy@ti.com>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Tero Kristo <t-kristo@ti.com>, Sudeep Holla <sudeep.holla@arm.com>,
        Santosh Shilimkar <ssantosh@kernel.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: Add TI SCI PM Domains
Organization: BayLibre
References: <20161019203347.17893-1-d-gerlach@ti.com>
        <20161019203347.17893-3-d-gerlach@ti.com>
        <7heg39pmgb.fsf@baylibre.com>
        <7f4754bb-7ded-6ce3-9558-a45b0d2b3888@ti.com>
Date: Mon, 24 Oct 2016 10:00:10 -0700
In-Reply-To: <7f4754bb-7ded-6ce3-9558-a45b0d2b3888@ti.com> (Dave Gerlach's
        message of "Fri, 21 Oct 2016 14:49:41 -0500")
Message-ID: <7h1sz51y3p.fsf@baylibre.com>
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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? ...
>>
>>> +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.

Ah, right.  I remember now.  This approach allows you to use a single
genpd as discussed earlier.

Makes sense now, suggestion retracted.

Kevin