Re: [PATCH v3 1/3] devicetree: bindings: Add optional dynamic-power-coefficient property

From: Rob Herring
Date: Mon Nov 09 2015 - 12:45:52 EST


On Mon, Nov 09, 2015 at 05:29:21PM +0000, Punit Agrawal wrote:
> The dynamic power consumption of a device is proportional to the
> square of voltage (V) and the clock frequency (f). It can be expressed as
>
> Pdyn = dynamic-power-coefficient * V^2 * f.
>
> The coefficient represents the running time dynamic power consumption in
> units of mw/MHz/uVolt^2 and can be used in the above formula to
> calculate the dynamic power in mW.

I have no issue with the binding, but I wonder if a single value is
really sufficient to model this. Don't you also need a static component?

Rob

>
> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> ---
> Documentation/devicetree/bindings/arm/cpus.txt | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
> index 91e6e5c..c33362d 100644
> --- a/Documentation/devicetree/bindings/arm/cpus.txt
> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> @@ -240,6 +240,23 @@ nodes to be present and contain the properties described below.
> Definition: Specifies the syscon node controlling the cpu core
> power domains.
>
> + - dynamic-power-coefficient
> + Usage: optional
> + Value type: <prop-encoded-array>
> + Definition: A u32 value that represents the running time dynamic
> + power coefficient in units of mW/MHz/uVolt^2. The
> + coefficient can either be calculated from power
> + measurements or derived by analysis.
> +
> + The dynamic power consumption of the CPU is
> + proportional to the square of the Voltage (V) and
> + the clock frequency (f). The coefficient is used to
> + calculate the dynamic power as below -
> +
> + Pdyn = dynamic-power-coefficient * V^2 * f
> +
> + where voltage is in uV, frequency is in MHz.
> +
> Example 1 (dual-cluster big.LITTLE system 32-bit):
>
> cpus {
> --
> 2.5.3
>
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