linux-kernel - Re: [RFC/RFT v2 12/14] arm64: dts: meson-g12a: enable DVFS on G12A boards

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Date:   Fri, 28 Jun 2019 11:08:22 -0700
From:   Kevin Hilman <khilman@...libre.com>
To:     Neil Armstrong <narmstrong@...libre.com>, jbrunet@...libre.com
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, martin.blumenstingl@...glemail.com,
        linux-gpio@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>
Subject: Re: [RFC/RFT v2 12/14] arm64: dts: meson-g12a: enable DVFS on G12A boards

Neil Armstrong <narmstrong@...libre.com> writes:

> Enable DVFS for the U200, SEI520 and X96-Max Amlogic G12A based board
> by setting the clock, OPP and supply for each CPU cores.
>
> The CPU cluster power supply can achieve 0.73V to 1.01V using a PWM
> output clocked at 800KHz with an inverse duty-cycle.
>
> DVFS has been tested by running the arm64 cpuburn at [1] and cycling
> between all the possible cpufreq translations and checking the final
> frequency using the clock-measurer, script at [2].
>
> [1] https://github.com/ssvb/cpuburn-arm/blob/master/cpuburn-a53.S
> [2] https://gist.github.com/superna9999/d4de964dbc0f84b7d527e1df2ddea25f
>
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>

[...]

> @@ -297,6 +316,34 @@
>  	status = "okay";
>  };
>  
> +&cpu0 {
> +	cpu-supply = <&vddcpu>;
> +	operating-points-v2 = <&cpu_opp_table>;
> +	clocks = <&clkc CLKID_CPU_CLK>;
> +	clock-latency = <50000>;
> +};
> +
> +&cpu1 {
> +	cpu-supply = <&vddcpu>;
> +	operating-points-v2 = <&cpu_opp_table>;
> +	clocks = <&clkc CLKID_CPU_CLK>;
> +	clock-latency = <50000>;
> +};
> +
> +&cpu2 {
> +	cpu-supply = <&vddcpu>;
> +	operating-points-v2 = <&cpu_opp_table>;
> +	clocks = <&clkc CLKID_CPU_CLK>;
> +	clock-latency = <50000>;
> +};
> +
> +&cpu3 {
> +	cpu-supply = <&vddcpu>;
> +	operating-points-v2 = <&cpu_opp_table>;
> +	clocks = <&clkc CLKID_CPU_CLK>;
> +	clock-latency = <50000>;
> +};

Just curious where this max clock transtion (clock-latency) value came
from.  Were you able to measure that somehow?

Kevin