Re: [PATCH] docs: dt-bindings: add DTS Coding Style document

[Conor Dooley <conor@kernel.org>]

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On Thu, Nov 16, 2023 at 07:12:18PM +0100, Krzysztof Kozlowski wrote:
> Document preferred coding style for Devicetree sources (DTS and DTSI),
> to bring consistency among all (sub)architectures and ease in reviews.

This is a good idea IMO, thanks for writing it.

Should we also mention in this about the expected breakdown of things
between $soc.dtsi and $soc-$board.dtsi? There's commonly confusion about
things like oscillators and where they belong - particularly when the
SoC mandates that these oscillators be of a single frequency.
It may seem obvious to us what goes where, but certainly contributors
frequently get this wrong.

Cheers,
Conor.

> 
> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Bjorn Andersson <andersson@kernel.org>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Heiko Stuebner <heiko@sntech.de>
> Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> Cc: Michal Simek <michal.simek@amd.com>
> Cc: Neil Armstrong <neil.armstrong@linaro.org>
> Cc: Nishanth Menon <nm@ti.com>
> Cc: Olof Johansson <olof@lixom.net>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> 
> ---
> 
> Merging idea: Rob/DT bindings
> ---
>  Documentation/devicetree/bindings/index.rst   |   1 +
>  .../devicetree/bindings/writing-dts.rst       | 137 ++++++++++++++++++
>  2 files changed, 138 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/writing-dts.rst
> 
> diff --git a/Documentation/devicetree/bindings/index.rst b/Documentation/devicetree/bindings/index.rst
> index d9002a3a0abb..975449be4862 100644
> --- a/Documentation/devicetree/bindings/index.rst
> +++ b/Documentation/devicetree/bindings/index.rst
> @@ -5,5 +5,6 @@
>  
>     ABI
>     writing-bindings
> +   writing-dts
>     writing-schema
>     submitting-patches
> diff --git a/Documentation/devicetree/bindings/writing-dts.rst b/Documentation/devicetree/bindings/writing-dts.rst
> new file mode 100644
> index 000000000000..10c477ec1eed
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/writing-dts.rst
> @@ -0,0 +1,137 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +.. _writingdts:
> +
> +===================================================
> +Writing Devicetree Sources (DTS) - DTS Coding Style
> +===================================================
> +
> +When writing Devicetree Sources (DTS) please observe below guidelines.  They
> +should be considered complementary to any rules expressed already in Devicetree
> +Specification and dtc compiler (including W=1 and W=2 builds).
> +
> +Individual architectures and sub-architectures can add additional rules, making
> +the style stricter.
> +
> +Naming and Valid Characters
> +---------------------------
> +
> +1. Node and property names are allowed to use only:
> +
> +   * lowercase characters:: [a-z]
> +   * digits:: [0-9]
> +   * dash:: -
> +
> +2. Labels are allowed to use only:
> +
> +   * lowercase characters:: [a-z]
> +   * digits:: [0-9]
> +   * underscore:: _
> +
> +3. Unit addresses should use lowercase hex, without leading zeros (padding).
> +
> +4. Hex values in properties, e.g. "reg", should use lowercase hex.  Any address
> +   part can be padded with leading zeros.
> +
> +Example::
> +
> +	gpi_dma2: dma-controller@800000 {
> +		compatible = "qcom,sm8550-gpi-dma", "qcom,sm6350-gpi-dma";
> +		reg = <0x0 0x00800000 0x0 0x60000>;
> +	}
> +
> +Order of Nodes
> +--------------
> +
> +1. Nodes within any bus, thus using unit addresses for children, shall be
> +   ordered incrementally by unit address.
> +
> +2. Nodes without unit addresses should be ordered alpha-numerically.
> +
> +3. When extending nodes in board DTS via &label, the entries should be ordered
> +   alpha-numerically.
> +
> +Example::
> +
> +	// SoC DTSI
> +
> +	\ {
> +		cpus {
> +			// ...
> +		};
> +
> +		psci {
> +			// ...
> +		};
> +
> +		soc@ {
> +			dma: dma-controller@10000 {
> +				// ...
> +			};
> +
> +			clk: clock-controller@80000 {
> +				// ...
> +			};
> +		};
> +	};
> +
> +	// Board DTS
> +
> +	&clk {
> +		// ...
> +	};
> +
> +	&dma {
> +		// ...
> +	};
> +
> +
> +Order of Properties in Device Node
> +----------------------------------
> +
> +Following order of properties in device nodes is preferred:
> +
> +1. compatible
> +2. reg
> +3. ranges
> +4. All properties with values
> +5. Boolean properties
> +6. status (if applicable)
> +7. Child nodes
> +
> +The "status" property is by default "okay", thus it can be omitted.
> +
> +Example::
> +
> +	// SoC DTSI
> +
> +	usb_1_hsphy: phy@88e3000 {
> +		compatible = "qcom,sm8550-snps-eusb2-phy";
> +		reg = <0x0 0x088e3000 0x0 0x154>;
> +		#phy-cells = <0>;
> +		resets = <&gcc GCC_QUSB2PHY_PRIM_BCR>;
> +		status = "disabled";
> +	};
> +
> +	// Board DTS
> +
> +	&usb_1_hsphy {
> +		clocks = <&tcsr TCSR_USB2_CLKREF_EN>;
> +		clock-names = "ref";
> +		status = "okay";
> +	};
> +
> +
> +Indentation
> +-----------
> +
> +1. Use indentation according to :ref:`codingstyle`.
> +2. For arrays spanning across lines, preferred is to align the continued
> +   entries with opening < from first line.
> +
> +Example::
> +
> +	thermal-sensor@c271000 {
> +		compatible = "qcom,sm8550-tsens", "qcom,tsens-v2";
> +		reg = <0x0 0x0c271000 0x0 0x1000>,
> +		      <0x0 0x0c222000 0x0 0x1000>;
> +	};
> -- 
> 2.34.1
> 

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