On Fri, Dec 13, 2024 at 12:03:05AM +0000, Ivy Huang wrote:
> From: Sumit Gupta <sumitg@xxxxxxxxxx>
>
> Access to safety cluster engine (SCE) fabric registers was blocked
> by firewall after the introduction of Functional Safety Island in
> Tegra234. After that, any access by software to SCE registers is
> correctly resulting in the internal bus error. However, when CPUs
> try accessing the SCE-fabric registers to print error info,
> another firewall error occurs as the fabric registers are also
> firewall protected. This results in a second error to be printed.
> Disable the SCE fabric node to avoid printing the misleading error.
> The first error info will be printed by the interrupt from the
> fabric causing the actual access.
>
> Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> Signed-off-by: Ivy Huang <yijuh@xxxxxxxxxx>
> ---
> arch/arm64/boot/dts/nvidia/tegra234.dtsi | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/boot/dts/nvidia/tegra234.dtsi b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> index d08faf6bb505..05a771ab1ed5 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> @@ -3815,7 +3815,7 @@
> compatible = "nvidia,tegra234-sce-fabric";
> reg = <0x0 0xb600000 0x0 0x40000>;
> interrupts = <GIC_SPI 173 IRQ_TYPE_LEVEL_HIGH>;
> - status = "okay";
> + status = "disabled";
> };
>
> rce-fabric@be00000 {
Hm... so what's the purpose of having this here if we can't use it? Are
there cases where we might want to access this? For example, could some
firmware *not* firewall this in some use-case, and would we want to use
this for error reporting in such cases?
I don't have a strong opinion on keeping this while being disabled. It
is a fairly small node, so it doesn't hurt much from that point of view,
but overall this patch seems like it's taking the easy way out.
For example if there's ever a case where we might want to use this, then
there should be some other entity (UEFI?) setting status = "disabled" at
runtime. Or perhaps it should be setting status = "okay" if it is not
firewalled. Generally if there's no mechanism that would ever change
status from "disabled" to "okay" at runtime, there's really no point in
having the node in DT.
Thierry
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