Re: [PATCH v2] docs: dt-bindings: add DTS Coding Style document

[Krzysztof Kozlowski]

On 20/11/2023 12:43, AngeloGioacchino Del Regno wrote:
> Il 20/11/23 09:40, Krzysztof Kozlowski ha scritto:
>> Document preferred coding style for Devicetree sources (DTS and DTSI),
>> to bring consistency among all (sub)architectures and ease in reviews.
>>
>> Cc: Andrew Davis <afd@xxxxxx>
>> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
>> Cc: Arnd Bergmann <arnd@xxxxxxxx>
>> Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
>> Cc: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>> Cc: Heiko Stuebner <heiko@xxxxxxxxx>
>> Cc: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
>> Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
>> Cc: Michal Simek <michal.simek@xxxxxxx>
>> Cc: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
>> Cc: Nishanth Menon <nm@xxxxxx>
>> Cc: Olof Johansson <olof@xxxxxxxxx>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
>>
>> ---
>>
>> Merging idea: Rob/DT bindings
>>
>> Changes in v2
>> =============
>> 1. Hopefully incorporate entire feedback from comments:
>> a. Fix \ { => / { (Rob)
>> b. Name: dts-coding-style (Rob)
>> c. Exceptions for ordering nodes by name for Renesas and pinctrl (Geert,
>>     Konrad)
>> d. Ordering properties by common/vendor (Rob)
>> e. Array entries in <> (Rob)
>>
>> 2. New chapter: Organizing DTSI and DTS
>>
>> 3. Several grammar fixes (missing articles)
>>
>> Cc: linux-rockchip@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-mediatek@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
>> Cc: linux-amlogic@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-arm-msm@xxxxxxxxxxxxxxx
>> ---
>>   .../devicetree/bindings/dts-coding-style.rst  | 163 ++++++++++++++++++
>>   Documentation/devicetree/bindings/index.rst   |   1 +
>>   2 files changed, 164 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/dts-coding-style.rst
>>
>> diff --git a/Documentation/devicetree/bindings/dts-coding-style.rst b/Documentation/devicetree/bindings/dts-coding-style.rst
>> new file mode 100644
>> index 000000000000..cc7e3b4d1b92
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/dts-coding-style.rst
>> @@ -0,0 +1,163 @@
>> +.. SPDX-License-Identifier: GPL-2.0
>> +.. _dtscodingstyle:
>> +
>> +=====================================
>> +Devicetree Sources (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).
> 
> This is imperative, so: s/should/shall/g

Sure, fine.

> 
>> +
>> +4. Hex values in properties, e.g. "reg", should use lowercase hex.  The address
>> +   part can be padded with leading zeros.
>> +
> 
> Same here, I'd say.... :-)
> 
>> +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.
>> +   Alternatively for some sub-architectures, nodes of the same type can be
>> +   grouped together (e.g. all I2C controllers one after another even if this
>> +   breaks unit address ordering).
>> +
>> +2. Nodes without unit addresses should be ordered alpha-numerically by the node
>> +   name.  For a few types of nodes, they can be ordered by the main property
>> +   (e.g. pin configuration states ordered by value of "pins" property).
>> +
>> +3. When extending nodes in the board DTS via &label, the entries should be
>> +   ordered alpha-numerically.
>> +
>> +Example::
>> +
> 
> Hmm, comments!
> 
>> +	// SoC DTSI
> 
> ....speaking of commenting, should we at least suggest to use C-style comments?
> 
> 	/* SoC DTSI */

I can switch it to C-style in the example, but we are going with Linux
Coding Style which soon will allow // judging by Linus' statements.

> 
>> +
>> +	/ {
>> +		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. Standard/common properties (defined by common bindings, e.g. without
>> +   vendor-prefixes)
>> +5. Vendor-specific properties
>> +6. status (if applicable)
>> +7. Child nodes, where each node is preceded with a blank line
>> +
>> +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";
>> +	};
> 
> Since this describes vendor-specific properties and vendor prefixes as well
> as standard properties, I think it would be clearer if we use something more
> complex that actually contains those as an example.
> 
> There's a few. One is MediaTek:
> 
> 	vdo1_rdma0: dma-controller@1c104000 {
> 		compatible = "mediatek,mt8195-vdo1-rdma";
> 		reg = <0 0x1c104000 0 0x1000>;
> 		#dma-cells = <1>;
> 		clocks = <&vdosys1 CLK_VDO1_MDP_RDMA0>;
> 		interrupts = <GIC_SPI 495 IRQ_TYPE_LEVEL_HIGH 0>;
> 		iommus = <&iommu_vdo M4U_PORT_L2_MDP_RDMA0>;
> 		power-domains = <&spm MT8195_POWER_DOMAIN_VDOSYS1>;
> 		mediatek,gce-client-reg = <&gce0 SUBSYS_1c10XXXX 0x4000 0x1000>;
> 	};
> 
> ...or other one can be nVidia:
> 
> 	mipi: mipi@700e3000 {
> 		compatible = "nvidia,tegra210-mipi";
> 		reg = <0x0 0x700e3000 0x0 0x100>;
> 		clocks = <&tegra_car TEGRA210_CLK_MIPI_CAL>;
> 		clock-names = "mipi-cal";
> 		power-domains = <&pd_sor>;
> 		#nvidia,mipi-calibrate-cells = <1>;
> 	};
> 
> ...or we could make an example out of fantasy, which could work even better
> as far as describing goes.
> 
> 	/* SoC DTSI */
> 
> 	device_node: device-class@6789abc {
> 		compatible = "vendor,device";

Yep. I'll use this, unless checkpatch complains about undocumented
compatible. :) This allows to show the child node.

> 		reg = <0 0x06789abc 0 0xa123>;
> 		ranges = <0 0 0x6789abc 0x1000>;
> 		#dma-cells = <1>;
> 		clocks = <&clock_controller SOC_CLOCK>;
> 		clock-names = "dev-clk";
> 		#vendor,custom-cells = <2>;
> 		status = "disabled";
> 
> 		child_node: child-class@100 {
> 			reg = <0x100 0x200>;
> 			/* ... */
> 		};
> 	};
> 
> 	/* Board DTS */
> 
> 	&device_node {
> 		device-supply = <&board_vreg1>;
> 		status = "okay";
> 	}
> 
>> +
>> +	// 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, it is preferred to align the continued
>> +   entries with opening < from the first line.
>> +3. Each entry in arrays with multiple cells (e.g. "reg" with two IO addresses)
>> +   should be enclosed in <>.
>> +
>> +Example::
>> +
>> +	thermal-sensor@c271000 {
>> +		compatible = "qcom,sm8550-tsens", "qcom,tsens-v2";
>> +		reg = <0x0 0x0c271000 0x0 0x1000>,
>> +		      <0x0 0x0c222000 0x0 0x1000>;
>> +	};
>> +
>> +Organizing DTSI and DTS
>> +-----------------------
>> +
>> +The DTSI and DTS files should be organized in a way representing the common
>> +(and re-usable) parts of the hardware.  Typically this means organizing DTSI
> 
>                                          ^^^^
> There's a double space here, it was probably unintentional.

I think I used everywhere double-spaces. At least this was my intention,
so I will fix single-spaces :)


Best regards,
Krzysztof