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

[Krzysztof Kozlowski]

Document preferred coding style for Devicetree sources (DTS and DTSI),
to bring consistency among all (sub)architectures and ease in reviews.

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
---
 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