linux-kernel - Re: [PATCH v2 2/3] dt-bindings: timer: Document arm, cortex-a7-timer in arch timer

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Date:   Thu, 17 Mar 2022 20:25:12 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Kuldeep Singh <singh.kuldeep87k@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/3] dt-bindings: timer: Document arm, cortex-a7-timer
 in arch timer

On 2022-03-17 19:15, Kuldeep Singh wrote:
> Renesas RZ/N1D platform uses compatible "arm,cortex-a7-timer" in
> conjugation with "arm,armv7-timer". Since, initial entry is not
> documented, it start raising dtbs_check warnings.
> 
> ['arm,cortex-a7-timer', 'arm,armv7-timer'] is too long
> 'arm,cortex-a7-timer' is not one of ['arm,armv7-timer', 'arm,armv8-timer']
> 'arm,cortex-a7-timer' is not one of ['arm,cortex-a15-timer']
> 
> Document this compatible to address it. The motivation to add this
> change is taken from an already existing entry "arm,cortex-a15-timer".
> Please note, this will not hurt any arch timer users.

Eh, if it's never been documented or supported, I say just get rid of 
it. The arch timer interface is by definition part of a CPU, and we can 
tell what the CPU is by reading its ID registers. Indeed that's how the 
driver handles the non-zero number of CPU-specific errata that already 
exist - we don't need compatibles for that.

In some ways it might have been nice to have *SoC-specific* compatibles 
given the difficulty some integrators seem to have had in wiring up a 
stable count *to* the interface, but it's not like they could be 
magically added to already-deployed DTs after a bug is discovered, and 
nor could we have mandated them from day 1 just in case and subsequently 
maintained a binding that is just an ever-growing list of every SoC. Oh 
well.

Robin.

> Signed-off-by: Kuldeep Singh <singh.kuldeep87k@...il.com>
> ---
>   Documentation/devicetree/bindings/timer/arm,arch_timer.yaml | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml b/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> index ba2910f0a7b2..ea390e5df71d 100644
> --- a/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> +++ b/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> @@ -26,6 +26,7 @@ properties:
>             - arm,armv8-timer
>         - items:
>             - enum:
> +              - arm,cortex-a7-timer
>                 - arm,cortex-a15-timer
>             - const: arm,armv7-timer
>