[PATCH v2] docs: dt-bindings: add DTS Coding Style document
Krzysztof Kozlowski
krzysztof.kozlowski at linaro.org
Mon Nov 20 06:57:15 PST 2023
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 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).
>
> 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 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::
>> +
>
> 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 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";
>> + };
>
> 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 at 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 at 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 at 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 at 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 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
>
> ^^^^
> 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
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