Re: [PATCH v2] arm64: dts: renesas: r8a78000: Fix GIC-720AE View 1 Redistributor description

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] DT fragmentation creates a booby trap leading to a fatal Data Abort if booted in View 0.
- [High] Splitting regions makes the GIC probe extremely brittle to sparse CPU topologies.
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commit ff8b7280cc2b6f0b2be6c7d236cd18a4ed49d89b
Author: Marek Vasut <marek.vasut+renesas@mailbox.org>

arm64: dts: renesas: r8a78000: Fix GIC-720AE View 1 Redistributor description

This commit splits the contiguous 8MB redistributor region into 32 separate
256KB regions. This attempts to work around the GIC-720AE View 1 behavior
where the first redistributor returns GICR_TYPER.Last == 1.

> diff --git a/arch/arm64/boot/dts/renesas/r8a78000.dtsi b/arch/arm64/boot/dts/renesas/r8a78000.dtsi
> index 4c97298fa7634..fd268604c0ec5 100644
> --- a/arch/arm64/boot/dts/renesas/r8a78000.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r8a78000.dtsi
> @@ -689,8 +689,40 @@ gic: interrupt-controller@39000000 {
>  			#interrupt-cells = <3>;
>  			#address-cells = <0>;
>  			interrupt-controller;
> -			reg = <0 0x39000000 0 0x10000>,
> -			      <0 0x39080000 0 0x800000>;
> +			#redistributor-regions = <32>;
> +			reg = <0x0 0x39000000 0x0 0x10000>,
> +			      <0x0 0x39080000 0x0 0x40000>,
> +			      <0x0 0x390c0000 0x0 0x40000>,

Could this cause a Data Abort if the system is booted in View 0?

Because the Device Tree binding doesn't currently support setting
single_redist = true for these regions, each 256KB region is mapped exactly
to that size via ioremap.

If booted in View 0, the hardware operates normally and intermediate
redistributors return GICR_TYPER.Last == 0.

The GIC driver's gic_iterate_rdists() inner loop relies entirely on the
GICR_TYPER.Last == 1 bit to break. Without it, the driver will advance ptr
and attempt to read gic_read_typer(ptr + GICR_TYPER) exactly at or beyond the
256KB ioremap boundary, triggering a Data Abort and kernel panic during early
boot.

Would it be safer to keep the DT as a single continuous region and add a
hardware-specific quirk to the GIC driver to bypass the LAST bit?

Additionally, does splitting these regions make the GIC probe brittle on
sparse CPU topologies?

If a redistributor is missing, such as a fused-off core, and returns an
invalid PIDR2, the driver will issue a warning and execute a break.

This break exits the entire outer for loop in gic_iterate_rdists(),
immediately aborting the discovery of all subsequent redistributor regions.

Any present CPUs located after a fused-off core would then fail to be
probed and will fail to boot.

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260514125328.20954-1-marek.vasut+renesas@mailbox.org?part=1