linux-kernel - Re: [PATCH v3 04/13] of: document new emc-timings subnode in nvidia,tegra124-car

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Message-ID: <545B172C.4060105@nvidia.com>
Date:	Thu, 6 Nov 2014 15:37:32 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	<linux-tegra@...r.kernel.org>
CC:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	"Thierry Reding" <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 04/13] of: document new emc-timings subnode in nvidia,tegra124-car

On 10/30/2014 01:22 AM, Tomeu Vizoso wrote:
> The EMC clock needs some extra information for changing its rate.
>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
>   .../bindings/clock/nvidia,tegra124-car.txt         | 46 +++++++++++++++++++++-
>   1 file changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt b/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
> index ded5d62..42e0588 100644
> --- a/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
> +++ b/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
> @@ -19,12 +19,35 @@ Required properties :
>     In clock consumers, this cell represents the bit number in the CAR's
>     array of CLK_RST_CONTROLLER_RST_DEVICES_* registers.
>
> +The node should contain a "emc-timings" subnode for each supported RAM type (see
> +field RAM_CODE in register PMC_STRAPPING_OPT_A), with its unit address being its
> +RAM_CODE.
> +
> +Required properties for "emc-timings" nodes :
> +- nvidia,ram-code : Should contain the value of RAM_CODE this timing set
> +  is used for.
> +
> +Each "emc-timings" node should contain a "timing" subnode for every supported
> +EMC clock rate. The "timing" subnodes should have the clock rate in Hz as their
> +unit address.

This seems to be a quite liberal use of unit addresses (same in the next 
patch) - is this allowed by DT?

> +
> +Required properties for "timing" nodes :
> +- clock-frequency : Should contain the memory clock rate to which this timing
> +relates.
> +- nvidia,parent-clock-frequency : Should contain the rate at which the current
> +parent of the EMC clock should be running at this timing.
> +- clocks : Must contain an entry for each entry in clock-names.
> +  See ../clocks/clock-bindings.txt for details.
> +- clock-names : Must include the following entries:
> +  - emc-parent : the clock that should be the parent of the EMC clock at this
> +timing.
> +
>   Example SoC include file:
>
>   / {
> -	tegra_car: clock {
> +	tegra_car: clock@0,60006000 {
>   		compatible = "nvidia,tegra124-car";
> -		reg = <0x60006000 0x1000>;
> +		reg = <0x0 0x60006000 0x0 0x1000>;
>   		#clock-cells = <1>;
>   		#reset-cells = <1>;
>   	};
> @@ -60,4 +83,23 @@ Example board file:
>   	&tegra_car {
>   		clocks = <&clk_32k> <&osc>;
>   	};
> +
> +	clock@0,60006000 {
> +		emc-timings@3 {
> +			nvidia,ram-code = <3>;
> +
> +			timing@...50000 {
> +				clock-frequency = <12750000>;
> +				nvidia,parent-clock-frequency = <408000000>;
> +				clocks = <&tegra_car TEGRA124_CLK_PLL_P>;
> +				clock-names = "emc-parent";
> +			};
> +			timing@...00000 {
> +				clock-frequency = <20400000>;
> +				nvidia,parent-clock-frequency = <408000000>;
> +				clocks = <&tegra_car TEGRA124_CLK_PLL_P>;
> +				clock-names = "emc-parent";
> +			};
> +		};
> +	};

At first it seems confusing to see a top-level node without a compatible 
property, until you realize it has already been defined before.

In patch 05, you put "Example board file:" above a similar node, which 
is enough to lift that ambiguity - could you do the same here?
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