[PATCH] arm64: dts: rockchip: Prevent thermal runaways in RK3308 SoC dtsi

[Jonas Karlman]

Hi Dragan,

On 2024-10-10 12:19, Dragan Simic wrote:
> Until the TSADC, thermal zones, thermal trips and cooling maps are defined
> in the RK3308 SoC dtsi, none of the CPU OPPs except the slowest one may be
> enabled under any circumstances.  Allowing the DVFS to scale the CPU cores
> up without even just the critical CPU thermal trip in place can rather easily
> result in thermal runaways and damaged SoCs, which is bad.
> 
> Thus, leave only the lowest available CPU OPP enabled for now.

This feel like a very aggressive limitation, to only allow the
opp-suspend rate, that is not even used under normal load.

I let my Rock Pi S board with a RK3308B variant run "stress -c 8" for
around 10 hours and the reported temp only reach around 50-55 deg c,
ambient temp around 20 deg c and board laying flat on a table without
any enclosure or heat sink.

This was running with performance as scaling_governor and cpu running
the 1008000 opp.

Most RK3308 variants datasheets list 1.3 GHz as max rate for CPU,
the K-variant lists 1.2 GHz, and the -S-variants seem to have both
reduced voltage and max rate.

The OPPs for this SoC already limits max rate to 1 GHz and is more than
likely good enough to not reach the max temperature of 115-125 deg c as
rated in datasheets and vendor DTs.

Adding the tsadc and trips (same/similar as px30) will probably allow us
to add/use the "missing" 1.2 and 1.3 GHz OPPs.

Regards,
Jonas

> 
> Fixes: 6913c45239fd ("arm64: dts: rockchip: Add core dts for RK3308 SOC")
> Cc: stable at vger.kernel.org
> Signed-off-by: Dragan Simic <dsimic at manjaro.org>
> ---
>  arch/arm64/boot/dts/rockchip/rk3308.dtsi | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk3308.dtsi b/arch/arm64/boot/dts/rockchip/rk3308.dtsi
> index 31c25de2d689..a7698e1f6b9e 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3308.dtsi
> +++ b/arch/arm64/boot/dts/rockchip/rk3308.dtsi
> @@ -120,16 +120,19 @@ opp-600000000 {
>  			opp-hz = /bits/ 64 <600000000>;
>  			opp-microvolt = <950000 950000 1340000>;
>  			clock-latency-ns = <40000>;
> +			status = "disabled";
>  		};
>  		opp-816000000 {
>  			opp-hz = /bits/ 64 <816000000>;
>  			opp-microvolt = <1025000 1025000 1340000>;
>  			clock-latency-ns = <40000>;
> +			status = "disabled";
>  		};
>  		opp-1008000000 {
>  			opp-hz = /bits/ 64 <1008000000>;
>  			opp-microvolt = <1125000 1125000 1340000>;
>  			clock-latency-ns = <40000>;
> +			status = "disabled";
>  		};
>  	};
>  
> 
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