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SubjectRe: [PATCH 2/2] dt-bindings: cpufreq: Document operating-points-v2-sunxi-cpu
Hi,

On Fri, Apr 05, 2019 at 06:24:55AM -0400, Yangtao Li wrote:
> Allwinner Process Voltage Scaling Tables defines the voltage and
> frequency value based on the speedbin blown in the efuse combination.
> The sunxi-cpufreq-nvmem driver reads the efuse value from the SoC to
> provide the OPP framework with required information.
> This is used to determine the voltage and frequency value for each
> OPP of operating-points-v2 table when it is parsed by the OPP framework.
>
> This change adds documentation for the DT bindings.
> The "operating-points-v2-sunxi-cpu" DT extends the "operating-points-v2"
> with following parameters:
> - nvmem-cells (NVMEM area containig the speedbin information)
> - opp-supported-hw: A single 32 bit bitmap value,
> representing compatible HW:
> 0: speedbin 0
> 1: speedbin 1
> 2: speedbin 2
> 3-31: unused
>
> Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
> ---
> .../bindings/opp/sunxi-nvmem-cpufreq.txt | 235 ++++++++++++++++++
> 1 file changed, 235 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/opp/sunxi-nvmem-cpufreq.txt
>
> diff --git a/Documentation/devicetree/bindings/opp/sunxi-nvmem-cpufreq.txt b/Documentation/devicetree/bindings/opp/sunxi-nvmem-cpufreq.txt
> new file mode 100644
> index 000000000000..80201d4e5147
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/opp/sunxi-nvmem-cpufreq.txt
> @@ -0,0 +1,235 @@
> +Allwinner Technologies, Inc. NVMEM CPUFreq and OPP bindings
> +===================================
> +
> +For some SoCs, the CPU frequency subset and voltage value of each OPP
> +varies based on the silicon variant in use. Allwinner Process Voltage
> +Scaling Tables defines the voltage and frequency value based on the
> +speedbin blown in the efuse combination. The sunxi-cpufreq-nvmem driver
> +reads the efuse value from the SoC to provide the OPP framework with
> +required information.
> +
> +Required properties:
> +--------------------
> +In 'cpus' nodes:
> +- operating-points-v2: Phandle to the operating-points-v2 table to use.
> +
> +In 'operating-points-v2' table:
> +- compatible: Should be
> + - 'operating-points-v2-sunxi-cpu'.
> +- nvmem-cells: A phandle pointing to a nvmem-cells node representing the
> + efuse registers that has information about the
> + speedbin that is used to select the right frequency/voltage
> + value pair.
> + Please refer the for nvmem-cells
> + bindings Documentation/devicetree/bindings/nvmem/nvmem.txt
> + and also examples below.
> +
> +In every OPP node:
> +- opp-supported-hw: A single 32 bit bitmap value, representing compatible HW.
> + Bitmap:
> + 0: speedbin 0
> + 1: speedbin 1
> + 2: speedbin 2
> + 3-31: unused

I'm wondering if that's the right approach.

I guess we could also have three different OPP tables, and pass them
all three through a phandle array, and have the kernel code select
which one is relevant based on the SID content

Another option would be to use the OF_DYNAMIC code to fill
operating-points-v2 at kernel boot, before (or when) cpufreq kicks in.

ATF could also do that work.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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