Re: [RFC PATCH 8/9] arm64: dts: renesas: r9a09g077: Use SYS syscon for WDTDCR access

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Removing the second `reg` entry breaks backward compatibility with older kernels.
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commit 4d641e4436b59e57d0434635cc0bb0ee418c05e5
Author: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

arm64: dts: renesas: r9a09g077: Use SYS syscon for WDTDCR access

This commit updates the r9a09g077 device tree to use the SYS syscon for
WDTDCR access. It removes the second reg entry from the watchdog nodes and
adds a new renesas,sys phandle property.

> diff --git a/arch/arm64/boot/dts/renesas/r9a09g077.dtsi b/arch/arm64/boot/dts/renesas/r9a09g077.dtsi
> index 59e5de7438261..b076bea9cb709 100644
> --- a/arch/arm64/boot/dts/renesas/r9a09g077.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r9a09g077.dtsi
> @@ -327,61 +327,61 @@ channel1 {
>  
>  		wdt0: watchdog@80082000 {
>  			compatible = "renesas,r9a09g077-wdt";
> -			reg = <0 0x80082000 0 0x400>,
> -			      <0 0x81295100 0 0x04>;
> +			reg = <0 0x80082000 0 0x400>;

Does removing the second reg entry cause a backward compatibility regression
with older kernels?

Device tree is considered a stable ABI, and older kernels lacking the
new syscon driver support might attempt to parse the second reg entry for
the WDTDCR register region.

Because the second entry is removed, devm_platform_ioremap_resource(pdev, 1)
would return an error, causing the watchdog driver to fail to probe.

Could the second reg entry be retained, or a new compatible string
introduced, to preserve DT ABI stability?

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260511185058.1926869-1-prabhakar.mahadev-lad.rj@bp.renesas.com?part=8