[PATCH] arm64: dts: rockchip: Describe why is HWRNG disabled in RK356x base dtsi

[Dragan Simic]

On 2024-12-02 15:44, Dragan Simic wrote:
> Despite the presence of the hardware random number generator (HWRNG) in 
> the
> different Rockchip RK356x SoC variants, it remains disabled for the 
> RK3566
> SoC because testing showed [1] that it produces unacceptably low 
> quality of
> random data, for some yet unknown reason.  The HWRNG is enabled for the 
> RK3568
> SoC, on which the testing showed good quality of the generated random 
> data.
> 
> To avoid possible confusion in the future, [2] let's have this 
> described
> briefly in the RK356x base SoC dtsi.
> 
> [1] 
> https://lore.kernel.org/linux-rockchip/cover.1720969799.git.daniel@makrotopia.org/T/#u
> [2] 
> https://lore.kernel.org/linux-rockchip/20241201234613.52322-1-pbrobinson@gmail.com/T/#u
> 
> Signed-off-by: Dragan Simic <dsimic at manjaro.org>

Oh, I forgot to Cc Peter as well while sending this patch, so I did
that now.  Sorry for the noise.

> ---
>  arch/arm64/boot/dts/rockchip/rk356x-base.dtsi | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
> b/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
> index 62be06f3b863..ab8f42c0a843 100644
> --- a/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
> +++ b/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
> @@ -1032,6 +1032,11 @@ sdhci: mmc at fe310000 {
>  		status = "disabled";
>  	};
> 
> +	/*
> +	 * Testing showed that the HWRNG found in RK3566 produces 
> unacceptably
> +	 * low quality of random data, so the HWRNG isn't enabled for all 
> RK356x
> +	 * SoC variants despite its presence.
> +	 */
>  	rng: rng at fe388000 {
>  		compatible = "rockchip,rk3568-rng";
>  		reg = <0x0 0xfe388000 0x0 0x4000>;