linux-kernel - Re: [PATCH 2/2] dt-bindings: cpufreq: Document operating-points-v2-sunxi-cpu

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Message-ID: <20190405145532.cstvbv3mxbzrmpxp@flea>
Date:   Fri, 5 Apr 2019 16:55:32 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Yangtao Li <tiny.windzz@...il.com>
Cc:     vireshk@...nel.org, nm@...com, sboyd@...nel.org,
        robh+dt@...nel.org, mark.rutland@....com, wens@...e.org,
        rjw@...ysocki.net, davem@...emloft.net, mchehab+samsung@...nel.org,
        gregkh@...uxfoundation.org, nicolas.ferre@...rochip.com,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...il.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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