Re: [PATCH v2 1/5] PM / OPP: extend DT binding to specify phandle of another node for OPP

[Rob Herring <robherring2@gmail.com>]

On 10/01/2013 08:32 AM, Sudeep KarkadaNagesha wrote:
> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
> 
> If more than one similar devices share the same operating points(OPPs)
> being in the same clock domain, currently we need to replicate the
> OPP entries in all the nodes.
> 
> This patch extends existing binding by adding a new property named
> 'operating-points-phandle' to specify the phandle in any device node
> pointing to another node which contains the actual OPP tuples.
> This helps to avoid replication if multiple devices share the OPPs.
> 
> Cc: Rob Herring <rob.herring@calxeda.com>
> Cc: Pawel Moll <pawel.moll@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Stephen Warren <swarren@wwwdotorg.org>
> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> Cc: Nishanth Menon <nm@ti.com>
> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
> ---
>  Documentation/devicetree/bindings/power/opp.txt | 161 ++++++++++++++++++++++--
>  1 file changed, 149 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/power/opp.txt b/Documentation/devicetree/bindings/power/opp.txt
> index 74499e5..f59b878 100644
> --- a/Documentation/devicetree/bindings/power/opp.txt
> +++ b/Documentation/devicetree/bindings/power/opp.txt
> @@ -4,22 +4,159 @@ SoCs have a standard set of tuples consisting of frequency and
>  voltage pairs that the device will support per voltage domain. These
>  are called Operating Performance Points or OPPs.
>  
> -Properties:
> +Required Properties:
>  - operating-points: An array of 2-tuples items, and each item consists
>    of frequency and voltage like <freq-kHz vol-uV>.
>  	freq: clock frequency in kHz
>  	vol: voltage in microvolt
>  
> +- operating-points-phandle: phandle to the device tree node which contains
> +	the operating points tuples(recommended to be used if multiple
> +	devices are in the same clock domain and hence share OPPs, as it
> +	avoids replication of OPPs)
> +
> +  operating-points and operating-points-phandle are mutually exclusive, only
> +  one of them can be present in any device node.
> +
>  Examples:
>  
> -cpu@0 {
> -	compatible = "arm,cortex-a9";
> -	reg = <0>;
> -	next-level-cache = <&L2>;
> -	operating-points = <
> -		/* kHz    uV */
> -		792000  1100000
> -		396000  950000
> -		198000  850000
> -	>;
> -};
> +1. A uniprocessor system (phandle not required)
> +
> +	cpu0: cpu@0 {
> +		compatible = "arm,cortex-a9";
> +		reg = <0>;
> +		operating-points = <
> +			/* kHz    uV */
> +			792000  1100000
> +			396000  950000
> +			198000  850000
> +		>;
> +	};
> +
> +2a. Consider a SMP system with 4 CPUs in the same clock domain(no phandle)
> +    Some existing DTs describe homogenous SMP systems by only listing the
> +    OPPs in the cpu@0 node. For compatiblity with existing DTs, an
> +    operating system may handle this case specially.
> +
> +	cpu0: cpu@0 {
> +		compatible = "arm,cortex-a9";
> +		reg = <0>;
> +		operating-points = <
> +			/* kHz    uV */
> +			792000  1100000
> +			396000  950000
> +			198000  850000
> +		>;
> +	};
> +
> +	cpu1: cpu@1 {
> +		compatible = "arm,cortex-a9";
> +		reg = <1>;
> +	};
> +
> +	cpu2: cpu@2 {
> +		compatible = "arm,cortex-a9";
> +		reg = <2>;
> +	};
> +
> +	cpu3: cpu@3 {
> +		compatible = "arm,cortex-a9";
> +		reg = <3>;
> +	};
> +
> +2b. Consider a SMP system with 4 CPUs in the same clock domain(with phandle)
> +    If more than one device of same type share the same OPPs, for example
> +    all the CPUs on a SoC or in a single cluster on a SoC, then we can avoid
> +    replicating the OPPs in all the nodes. We can specify the phandle of
> +    the node which contains the OPP tuples instead.
> +
> +	cpu0: cpu@0 {
> +		compatible = "arm,cortex-a9";
> +		reg = <0>;
> +		operating-points-phandle = <&cpu_opp>;
> +	};
> +
> +	cpu1: cpu@1 {
> +		compatible = "arm,cortex-a9";
> +		reg = <1>;
> +		operating-points-phandle = <&cpu_opp>;
> +	};
> +
> +	cpu2: cpu@2 {
> +		compatible = "arm,cortex-a9";
> +		reg = <2>;
> +		operating-points-phandle = <&cpu_opp>;
> +	};
> +
> +	cpu3: cpu@3 {
> +		compatible = "arm,cortex-a9";
> +		reg = <3>;
> +		operating-points-phandle = <&cpu_opp>;
> +	};
> +
> +	opps-table {
> +		cpu_opp: cpu_opp {
> +			operating-points = <
> +				/* kHz    uV */
> +				792000  1100000
> +				396000  950000
> +				198000  850000
> +			>;
> +		};
> +		... /* other device OPP nodes */

But this is a subnode of /cpus. IMO, OPPs should be located near what
they control.


> +	}
> +
> +4. Consider an AMP(asymmetric multi-processor) sytem with 2 clusters of
> +   CPUs. Each cluster has 2 CPUs and all the CPUs within the cluster share
> +   the clock domain.
> +
> +	cpu0: cpu@0 {
> +		compatible = "arm,cortex-a15";
> +		reg = <0>;
> +		operating-points-phandle = <&cluster0_opp>;
> +	};
> +
> +	cpu1: cpu@1 {
> +		compatible = "arm,cortex-a15";
> +		reg = <1>;
> +		operating-points-phandle = <&cluster0_opp>;
> +	};
> +
> +	cpu2: cpu@100 {
> +		compatible = "arm,cortex-a7";
> +		reg = <100>;
> +		operating-points-phandle = <&cluster1_opp>;
> +	};
> +
> +	cpu3: cpu@101 {
> +		compatible = "arm,cortex-a7";
> +		reg = <101>;
> +		operating-points-phandle = <&cluster1_opp>;
> +	};
> +
> +	opps-table {
> +		cluster0_opp: cluster0_opp {

Why not use the cpu topology? Then the operating point can apply to
cores based on the position in the topology. You don't even need a
phandle in that case. You can look for OPPs in either a cpu node or in
the topology.


> +			operating-points = <
> +				/* kHz    uV */
> +				792000  1100000
> +				396000  950000
> +				198000  850000
> +			>;
> +		};
> +		cluster1_opp: cluster1_opp {
> +			operating-points = <
> +				/* kHz    uV */
> +				792000  950000
> +				396000  750000
> +				198000  450000
> +			>;
> +		};
> +		... /* other device OPP nodes */
> +	}
> +
> +Container Node
> +--------------
> +	- It's highly recommended to place all the shared OPPs under single
> +	  node for consistency and better readability
> +	- It's quite similar to clocks or pinmux container nodes
> +	- In the above examples, "opps-table" is the container node
>