Re: [PATCH v7 8/8] arm64: dts: renesas: r9a09g087: Use CPG/MSSR syscon for WDTDCR access

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Critical] dt-bindings: removing second 'reg' entry breaks old kernel compatibility
--

commit 74168eab64567b9dfb3f02ff14712a6e81564a41
Author: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

arm64: dts: renesas: r9a09g087: Use CPG/MSSR syscon for WDTDCR access

This commit updates the device tree to replace the direct mapping of
individual WDTDCR registers with a syscon phandle to the CPG/MSSR block.
This consolidates the multi-function block access via a unified syscon
regmap interface.

> diff --git a/arch/arm64/boot/dts/renesas/r9a09g087.dtsi b/arch/arm64/boot/dts/renesas/r9a09g087.dtsi
> index 68c8daed557bd..abca7aa894589 100644
> --- a/arch/arm64/boot/dts/renesas/r9a09g087.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r9a09g087.dtsi
> @@ -327,61 +327,61 @@ channel1 {
>  
>  		wdt0: watchdog@80082000 {
>  			compatible = "renesas,r9a09g087-wdt", "renesas,r9a09g077-wdt";
> -			reg = <0 0x80082000 0 0x400>,
> -			      <0 0x81295100 0 0x04>;
> +			reg = <0 0x80082000 0 0x400>;

[Severity: Critical]
Does removing the second reg entry here break backward compatibility with
older kernels?

Device tree bindings are typically treated as a stable ABI, meaning newer
device trees should be able to boot older kernels. The rzv2h_wdt driver
in existing kernels unconditionally calls:

devm_platform_ioremap_resource(pdev, 1)

for this compatible string. By completely removing the second reg entry at
index 1, older kernels might fail to probe the watchdog entirely. Is there
a way to deprecate this gracefully or retain the second reg entry for
compatibility?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260929105021.542730-1-prabhakar.mahadev-lad.rj@bp.renesas.com?part=8