[PATCH v2] 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: Andrew Davis <afd at ti.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Bjorn Andersson <andersson at kernel.org>
Cc: Geert Uytterhoeven <geert+renesas at glider.be>
Cc: Heiko Stuebner <heiko at sntech.de>
Cc: Konrad Dybcio <konrad.dybcio at linaro.org>
Cc: Matthias Brugger <matthias.bgg at gmail.com>
Cc: Michal Simek <michal.simek at amd.com>
Cc: Neil Armstrong <neil.armstrong at linaro.org>
Cc: Nishanth Menon <nm at ti.com>
Cc: Olof Johansson <olof at lixom.net>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski at linaro.org>

---

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 at lists.infradead.org
Cc: linux-mediatek at lists.infradead.org
Cc: linux-samsung-soc at vger.kernel.org
Cc: linux-amlogic at lists.infradead.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-arm-msm at vger.kernel.org
---
 .../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).
+
+4. Hex values in properties, e.g. "reg", should use lowercase hex.  The address
+   part can be padded with leading zeros.
+
+Example::
+
+	gpi_dma2: dma-controller at 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::
+
+	// SoC DTSI
+
+	/ {
+		cpus {
+			// ...
+		};
+
+		psci {
+			// ...
+		};
+
+		soc@ {
+			dma: dma-controller at 10000 {
+				// ...
+			};
+
+			clk: clock-controller at 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 at 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, 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 at 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
+and DTS files into several files:
+
+1. DTSI with contents of the entire SoC (without nodes for hardware not present
+   on the SoC).
+2. If applicable: DTSI with common or re-usable parts of the hardware (e.g.
+   entire System-on-Module).
+3. DTS representing the board.
+
+Hardware components which are present on the board should be placed in the
+board DTS, not in the SoC or SoM DTSI.  A partial exception is a common
+external reference SoC-input clock, which could be coded as a fixed-clock in
+the SoC DTSI with its frequency provided by each board DTS.
diff --git a/Documentation/devicetree/bindings/index.rst b/Documentation/devicetree/bindings/index.rst
index d9002a3a0abb..cc1fbdc05657 100644
--- a/Documentation/devicetree/bindings/index.rst
+++ b/Documentation/devicetree/bindings/index.rst
@@ -4,6 +4,7 @@
    :maxdepth: 1
 
    ABI
+   dts-coding-style
    writing-bindings
    writing-schema
    submitting-patches
-- 
2.34.1