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

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@manjaro.org>
Reviewed-by: Diederik de Haas <didi.debian@cknow.org>
Link: https://lore.kernel.org/r/6b272e2f8f916c04b05db50df621659a5a7f29ab.1733149874.git.dsimic@manjaro.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

diff --git a/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi b/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
index e5539062911405926c674464beb6455feb689856..de5e6c0c3d24921d439f8e821f47680a8fa0c96d 100644 (file)
--- a/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk356x-base.dtsi
@@ -1032,6 +1032,11 @@
                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@fe388000 {
                compatible = "rockchip,rk3568-rng";
                reg = <0x0 0xfe388000 0x0 0x4000>;