linux-kernel - Re: [PATCH 2/7] dt-bindings: watchdog: Document Exynos850 watchdog bindings

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Date:   Fri, 29 Oct 2021 10:02:03 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Rob Herring <robh+dt@...nel.org>
Cc:     linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 2/7] dt-bindings: watchdog: Document Exynos850 watchdog
 bindings

On 28/10/2021 20:35, Sam Protsenko wrote:
> Exynos850 SoC has two CPU clusters:
>   - cluster 0: contains CPUs #0, #1, #2, #3
>   - cluster 1: contains CPUs #4, #5, #6, #7
> 
> Each cluster has its own dedicater watchdog timer. Those WDT instances
> are controlled using different bits in PMU registers, so there should be
> two different compatible strings (for each cluster), to tell the driver
> which bits to use for each WDT instance.
> 
> Also on Exynos850 the peripheral clock and the source clock are two
> different clocks. Provide a way to specify two clocks in watchdog device
> tree node.
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> ---
>  .../devicetree/bindings/watchdog/samsung-wdt.yaml  | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml b/Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml
> index 93cd77a6e92c..19c7f7767559 100644
> --- a/Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml
> +++ b/Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml
> @@ -22,16 +22,24 @@ properties:
>        - samsung,exynos5250-wdt                # for Exynos5250
>        - samsung,exynos5420-wdt                # for Exynos5420
>        - samsung,exynos7-wdt                   # for Exynos7
> +      - samsung,exynos850-cl0-wdt             # for Exynos850 (CPU cluster 0)
> +      - samsung,exynos850-cl1-wdt             # for Exynos850 (CPU cluster 1)

I would prefer to have one compatible and additional u32 property
pointing to cluster index. The driver would use this property to adjust
the PMU register offsets or bits.

Why? Because if next time you have three clusters, you will need to make
three compatibles for something which differs by only two register
offsets. Both watchdog instances (or three in some unspecified future)
are here the same, they just control different blocks, therefore should
accept some parameter instead of making them different compatibles.

>  
>    reg:
>      maxItems: 1
>  
>    clocks:
> -    maxItems: 1
> +    minItems: 1
> +    items:
> +      - description: Peripheral clock used for register interface; if it's the
> +                     only clock, it's also a source clock
> +      - description: Source clock (optional)
>  
>    clock-names:
> +    minItems: 1
>      items:
>        - const: watchdog
> +      - const: watchdog_src

Don't you require src clock on Exynos850?



Best regards,
Krzysztof