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

Krzysztof Kozlowski
2023-11-20T08:41:40Z

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@ti.com>
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

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@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-amlogic@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arm-msm@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@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@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";
+ };
+
+ // 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
+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