linux-kernel - Re: [PATCH v2 1/4] arm64: dts: ti: k3-am65-main: Disable RNG node

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Date:   Thu, 7 Jul 2022 09:44:00 -0500
From:   Bryan Brattlof <bb@...com>
To:     Andrew Davis <afd@...com>
CC:     Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] arm64: dts: ti: k3-am65-main: Disable RNG node

Hi Andrew

On July  6, 2022 thus sayeth Andrew Davis:
> The hardware random number generator is used by OP-TEE and is access is
> denied to other users with SoC level bus firewalls. Any access to this
> device from Linux will result in firewall errors. Disable this node.
> 
> Signed-off-by: Andrew Davis <afd@...com>
> ---
> 
> Changes from v1:
>  - Added comment in dtsi file
> 
>  arch/arm64/boot/dts/ti/k3-am65-main.dtsi | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/boot/dts/ti/k3-am65-main.dtsi b/arch/arm64/boot/dts/ti/k3-am65-main.dtsi
> index e749343accedd..9de5a8294acd6 100644
> --- a/arch/arm64/boot/dts/ti/k3-am65-main.dtsi
> +++ b/arch/arm64/boot/dts/ti/k3-am65-main.dtsi
> @@ -127,6 +127,7 @@ rng: rng@...0000 {
>  			reg = <0x0 0x4e10000 0x0 0x7d>;
>  			interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>;
>  			clocks = <&k3_clks 136 1>;
> +			status = "disabled"; /* Used by OP-TEE */

Just curious about how we should document disabling nodes. I was 
assuming the reasoning should be described in the bindings?

I would like to start disabling nodes by default in our dtsi files and 
enabling them in our top dts file, making it easier for others to use 
our device tree for a more focused purpose than our dev boards. I just 
didn't know where I should document why I disabled the nodes :)

~Bryan