linux-kernel - Re: [PATCH] arm64: dts: mt8173: add clock

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Date:	Thu, 18 Jun 2015 18:15:03 +0200
From:	Heiko Stuebner <heiko@...ech.de>
To:	linux-mediatek@...ts.infradead.org
Cc:	Eddie Huang <eddie.huang@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	devicetree@...r.kernel.org, James Liao <jamesjj.liao@...iatek.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: dts: mt8173: add clock_null

Am Donnerstag, 18. Juni 2015, 13:29:11 schrieb Eddie Huang:
> Add clk_null, which represents clocks that can not / need not
> controlled by software.
> There are many clocks' parent set to clk_null.

Devicetree is supposed to describe hardware, and ideally not what software 
does with it. If the clock simply cannot be controlled by software, it will 
still have a rate and I think it should probably be modelled - similarly we 
sometimes have fixed regulators that also are not software controllable.


While it might be ok to define dummy clocks as a temporary stopgap, these 
should definitly be marked as such. This clk_null at least sounds like there is 
no plan to replace this with a real solution at some point.

And of course a bit of context would be cool, to know which type of clocks 
this actually replaces.


Heiko

> Signed-off-by: James Liao <jamesjj.liao@...iatek.com>
> Signed-off-by: Eddie Huang <eddie.huang@...iatek.com>
> ---
> Base on 4.1-rc1
> 
> Change-Id: I4db9b40d07e28f54f7bae9b676316cbd6a962124
> ---
>  arch/arm64/boot/dts/mediatek/mt8173.dtsi | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi
> b/arch/arm64/boot/dts/mediatek/mt8173.dtsi index 924fdb6..4798f44 100644
> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi
> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi
> @@ -81,6 +81,12 @@
>  		cpu_on	      = <0x84000003>;
>  	};
> 
> +	clk_null: clk_null {
> +		compatible = "fixed-clock";
> +		clock-frequency = <0>;
> +		#clock-cells = <0>;
> +	};
> +
>  	uart_clk: dummy26m {
>  		compatible = "fixed-clock";
>  		clock-frequency = <26000000>;

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