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Date: Mon, 20 Nov 2023 08:19:48 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Rob Herring <robh+dt@...nel.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>,
Arnd Bergmann <arnd@...db.de>,
Bjorn Andersson <andersson@...nel.org>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Heiko Stuebner <heiko@...ech.de>,
Konrad Dybcio <konrad.dybcio@...aro.org>,
Matthias Brugger <matthias.bgg@...il.com>,
Michal Simek <michal.simek@....com>,
Neil Armstrong <neil.armstrong@...aro.org>,
Nishanth Menon <nm@...com>, Olof Johansson <olof@...om.net>
Subject: Re: [PATCH] docs: dt-bindings: add DTS Coding Style document
On 16/11/2023 21:44, Rob Herring wrote:
>>
>> 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
>
> Perhaps dts-coding-style.rst
Ack
>
> After adding writing-schema, I realized the difference between
> writing-schema and writing-bindings isn't all that clear. I never got
> around to renaming things.
>
>>
>> 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).
>
> Strictly speaking, the unit-address is whatever a bus defines, but
> yes, by default, that is the format.
>
>> +
>> +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@...000 {
>> + 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.
>
> Or matching the original node definition order?
If there is any sub-arch using such style, then sure, why not. Otherwise
if we do not have such examples, I find that a bit tricky to implement:
for patches adding new board, one needs to check the original DTSI for
order.
>
>> +
>> +Example::
>> +
>> + // SoC DTSI
>> +
>> + \ {
>
> / {
>
>> + cpus {
>> + // ...
>> + };
>> +
>> + psci {
>> + // ...
>> + };
>> +
>> + soc@ {
>> + dma: dma-controller@...00 {
>> + // ...
>> + };
>> +
>> + clk: clock-controller@...00 {
>> + // ...
>> + };
>> + };
>> + };
>> +
>> + // 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
>
> I make this like schemas, standard/common properties first, then
> vendor specific properties.
Sure.
>
>> +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@...3000 {
>> + 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@...1000 {
>> + compatible = "qcom,sm8550-tsens", "qcom,tsens-v2";
>> + reg = <0x0 0x0c271000 0x0 0x1000>,
>> + <0x0 0x0c222000 0x0 0x1000>;
>
> You should cover the <> style too, meaning <> around each logical entry.
Ack.
Best regards,
Krzysztof
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