Re: [PATCH v2 4/6] dt-bindings: watchdog: renesas: Document `renesas,syscon-cpg-error-rst` property

[Rob Herring <robh@kernel.org>]

On Fri, Dec 27, 2024 at 07:02:08PM +0000, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> 
> The RZ/V2H(P) CPG block includes Error Reset Registers (CPG_ERROR_RSTm).
> A system reset is triggered in response to error interrupt factors, and
> the corresponding bit is set in the CPG_ERROR_RSTm register. These
> registers can be utilized by various IP blocks as needed.
> 
> In the event of a watchdog overflow or underflow, a system reset is issued,
> and the CPG_ERROR_RST2[0/1/2/3] bits are set depending on the watchdog in
> use: CM33 = 0, CA55 = 1, CR8_0 = 2, CR8_1 = 3. For the watchdog driver to
> determine and report the current boot status, it needs to read the
> CPG_ERROR_RST2[0/1/2/3]bits and provide this information to the user upon
> request.
> 
> To facilitate this operation, add `renesas,syscon-cpg-error-rst`
> property to the WDT node, which maps to the `syscon` CPG node, enabling
> retrieval of the necessary information.
> 
> Additionally, the property is marked as required for the RZ/V2H(P) SoC to
> ensure future compatibility (e.g., where the same IP block is present on
> the RZ/G3E SoC) and explicitly disallowed for other SoCs.

This is the other half of the ABI change. 

> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> ---
> v1->v2
> - Renamed `renesas,r9a09g057-syscon-wdt-errorrst` to `renesas,syscon-cpg-error-rst`
> - Updated commit message
> ---
>  .../bindings/watchdog/renesas,wdt.yaml          | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml b/Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml
> index 29ada89fdcdc..ca62ae8b1b0c 100644
> --- a/Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml
> +++ b/Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml
> @@ -112,6 +112,19 @@ properties:
>  
>    timeout-sec: true
>  
> +  renesas,syscon-cpg-error-rst:
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    description:
> +      The first cell is a phandle to the SYSCON entry required to obtain
> +      the current boot status. The second cell specifies the CPG_ERROR_RSTm
> +      register offset within the SYSCON, and the third cell indicates the
> +      bit within the CPG_ERROR_RSTm register.
> +    items:
> +      - items:
> +          - description: Phandle to the CPG node
> +          - description: The CPG_ERROR_RSTm register offset
> +          - description: The bit within CPG_ERROR_RSTm register of interest
> +
>  required:
>    - compatible
>    - reg
> @@ -182,7 +195,11 @@ allOf:
>        properties:
>          interrupts: false
>          interrupt-names: false
> +      required:
> +        - renesas,syscon-cpg-error-rst

New required property == ABI break

Once the OS driver relies on this being present, then older DTs will 
break.

That's all fine if you spell it out in the commit message and any users 
are fine with the breakage.

Rob