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

AngeloGioacchino Del Regno
2023-11-21T10:25:50Z

Il 20/11/23 15:57, Krzysztof Kozlowski ha scritto:
> 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@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).
>>
>> 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@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.
>

Right. That wasn't a strong opinion anyway, so it's totally okay as well.

>>
>>> +
>>> + / {
>>> + 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";
>>> + };
>>
>> 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@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@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@6789abc {
>> compatible = "vendor,device";
>
> Yep. I'll use this, unless checkpatch complains about undocumented
> compatible. :) This allows to show the child node.
>

If checkpatch complains about undocumented compatible, could we perhaps use one
that does actually exist, while still retaining the actual mockup examples?

I understand the eventual concern about somewhat wrongly documenting said device,
but it's also true that this is documentation about something else that is not
related to a specific device (so perhaps a "warning: this is for representation
purposes only, and may contain properties that the devices pointed by the currently
used compatible string may not accept" might work to avoid confusion?).

>> 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@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@c271000 {
>>> + compatible = "qcom,sm8550-tsens", "qcom,tsens-v2";
>>> + reg = <0x0 0x0c271000 0x0 0x1000>,
>>> + <0x0 0x0c222000 0x0 0x1000>;
>>> + };
>>> +
>>> +Organizing DTSI and DTSthat
>>> +-----------------------
>>> +
>>> +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 :)
>

Oh! Okay, yeah, that also works :-D

Cheers,
Angelo