linux-kernel - Re: [PATCH 4/7] dt-bindings: chosen: Add clocksource and clockevent selection

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Message-ID: <81da473f-54d7-2a00-61ec-9351cdfcaaf3@baylibre.com>
Date:   Wed, 11 Sep 2019 09:34:27 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>,
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Subject: Re: [PATCH 4/7] dt-bindings: chosen: Add clocksource and clockevent
 selection

Hi,

On 10/09/2019 15:47, Claudiu Beznea wrote:
> From: Alexandre Belloni <alexandre.belloni@...tlin.com>
> 
> Some timer drivers may behave either as clocksource or clockevent
> or both. Until now, in case of platforms with multiple hardware
> resources of the same type, the drivers were chosing the first
> registered hardware resource as clocksource/clockevent and the
> next one as clockevent/clocksource. Other were using different
> compatibles (one for each functionality, although its about the
> same hardware). Add DT bindings to be able to choose the
> functionality of a timer.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
> ---
>  Documentation/devicetree/bindings/chosen.txt | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 45e79172a646..aad3034cdbdf 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -135,3 +135,23 @@ e.g.
>  		linux,initrd-end = <0x82800000>;
>  	};
>  };
> +
> +linux,clocksource and linux,clockevent
> +--------------------------------------
> +
> +Those nodes have a timer property. This property is a phandle to the timer to be
> +chosen as the clocksource or clockevent. This is only useful when the platform
> +has multiple identical timers and it is not possible to let linux make the
> +correct choice.
> +
> +/ {
> +	chosen {
> +		linux,clocksource {
> +			timer = <&timer0>;
> +		};
> +
> +		linux,clockevent {
> +			timer = <&timer1>;
> +		};
> +	};
> +};
> 

Why not in aliases ?

aliases {
    clocksource0 = &timer0;
    clockevent0 = &timer1;
};

since we can have multiple of each, we should not limit ourselves to 1 clkevent
and 1 clksource.

In the aliases case, each driver would expose both capabilities, and the core would select
what to enable.

Neil