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

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Message-ID: <7f4754bb-7ded-6ce3-9558-a45b0d2b3888@ti.com>
Date:   Fri, 21 Oct 2016 14:49:41 -0500
From:   Dave Gerlach <d-gerlach@...com>
To:     Kevin Hilman <khilman@...libre.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-pm@...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

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? ...
>
>> +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.

Regards,
Dave

[1] http://www.spinics.net/lists/arm-kernel/msg524151.html

>
> Kevin
>