[PATCH v3] docs: dt-bindings: add DTS Coding Style document

[Krzysztof Kozlowski]

On 28/11/2023 21:00, Dragan Simic wrote:
>> 5. Allow two style of ordering overrides in board DTS: alphabetically 
>> or
>>    by order of DTSI (Rob).
>> 6. I did not incorporate feedback about, due to lack of consensus and 
>> my
>>    disagreement:
>>    a. SoM being DTS without DTSI in "Organizing DTSI and DTS"
> 
> I went through the language of the entire patch, after the notice that 
> the v4 would no longer accept language improvements.  My wording- and 
> grammar-related suggestions are available inline below.

Thanks. I want to finish this at some point and it might not happen if
grammar fixes will be coming every patch revision. Then after we finish
review, new feedback will appear about using British or American
spelling (which reminds me old quote/email about which variant of
English is most popular in Linux kernel: the incorrect one).

> 
>> 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
>> Cc: workflows at vger.kernel.org
>> Cc: linux-doc at vger.kernel.org
>> ---
>>  .../devicetree/bindings/dts-coding-style.rst  | 194 ++++++++++++++++++
>>  Documentation/devicetree/bindings/index.rst   |   1 +
>>  2 files changed, 195 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..e374bec0f555
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/dts-coding-style.rst
>> @@ -0,0 +1,194 @@
>> +.. SPDX-License-Identifier: GPL-2.0
>> +.. _dtscodingstyle:
>> +
>> +=====================================
>> +Devicetree Sources (DTS) Coding Style
>> +=====================================
>> +
>> +When writing Devicetree Sources (DTS) please observe below guidelines. 
>>  They
> 
> The sentence above should be replaced with: "The following guidelines 
> are to be followed when writing Devicetree Source (DTS) files."

Are you sure? It's passive and I was taught it is discouraged for
writing. See for example:
https://www.hamilton.edu/academics/centers/writing/seven-sins-of-writing/1

> 
>> +should be considered complementary to any rules expressed already in 
>> Devicetree
>> +Specification and dtc compiler (including W=1 and W=2 builds).
> 
> A definite article ("the") should be added before "Devicetree 

ack

> Specification" and "dtc".  Also, "Specification" in "Devicetree 
> Specification" should be capitalized.

It was.


> 
>> +
>> +Individual architectures and sub-architectures can add additional 
>> rules, making
>> +the style stricter.
> 
> "Sub-architectures" should be replaced with "subarchitectures".  "Can 

A hint, you can write such review feedback as:
s/sub-architectures/subarchitectures/

BTW, my language spelling points "subarchitectures" as mistake, but
sure, ack.

> add" should be replaced with "can define".   "Style" should be replaced 
> with "coding style".

ack

> 
>> +
>> +Naming and Valid Characters
>> +---------------------------
>> +
>> +Devicetree specification allows broader range of characters in node 
>> and
>> +property names, but for code readability the choice shall be narrowed.
> 
> The definite article ("the") should be added before "Devicetree 
> Specification", and "specification" should be capitalised.  As already 
> suggested, "broader range" should be replaced with "a broad range".  
> "But for code readability the choice shall be narrowed" should be 
> replaced with "but this coding style narrows the range down to achieve 
> better code readability".

Ack

> 
>> +
>> +1. Node and property names are allowed to use only:
> 
> "Are allowed to" should be replaced with "can".  After "only", "the 
> following characters" should be added.

ack

> 
>> +
>> +   * lowercase characters: [a-z]
>> +   * digits: [0-9]
>> +   * dash: -
> 
> List items should be capitalized, i.e. "Lowercase characters" should be 
> used instead of "lowercase characters", etc.

ack

> 
>> +
>> +2. Labels are allowed to use only:
> 
> "Are allowed to" should be replaced with "can".  After "only", "the 
> following characters" should be added.
> 
ack

>> +
>> +   * lowercase characters: [a-z]
>> +   * digits: [0-9]
>> +   * underscore: _
> 
> List items should be capitalized, i.e. "Lowercase characters" should be 
> used instead of "lowercase characters", etc.
> 

ack

>> +
>> +3. Unit addresses shall use lowercase hex, without leading zeros 
>> (padding).
> 
> "Lowercase hex" should be replaced with "lowercase hexadecimal digits".
> 
>> +
>> +4. Hex values in properties, e.g. "reg", shall use lowercase hex.  The 
>> address
>> +   part can be padded with leading zeros.
> 
> "Hex values" should be replaced with "Hexadecimal values".  "Lowercase 
> hex" should be replaced with "lowercase hexadecimal digits".

ack, but that's quite picky. We are (software) engineers so we are
supposed to know the slang.

> 
>> +
>> +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
> 
> "Within" should be replaced "on".

ack

> 
>> +   ordered incrementally by unit address.
> 
> Should be replaced with "ordered by unit address in ascending order".

ack

> 
>> +   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).
> 
> "Sub-architectures" should be replaced with "subarchitectures".  The 
> "(e.g. ...)" form should be replaced with ", e.g. ...".

ack

> 
>> +
>> +2. Nodes without unit addresses shall 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).
> 
> "Alpha-numerically" should be replaced with "alphabetically".  

Are you sure? Does alphabetical order include numbers?

> "Types of 
> nodes" should be replaced with "node types".  The "(e.g. ...)" form 
> should be replaced with ", e.g. ...".

ack

> 
>> +
>> +3. When extending nodes in the board DTS via &label, the entries shall 
>> be
>> +   ordered either alpha-numerically or by keeping the order from DTSI 
>> (choice
>> +   depending on sub-architecture).
> 
> "Alpha-numerically" should be replaced with "alphabetically".  

Similar concern

> "Sub-architecture" should be replaced with "subarchitecture".  "(Choice 
> depending on sub-architecture)" should be replaced with ", where the 
> choice depends on the subarchitecture".

ack

> 
>> +
>> +Above ordering rules are easy to enforce during review, reduce chances 
>> of
>> +conflicts for simultaneous additions (new nodes) to a file and help in
>> +navigating through the DTS source.
> 
> "Above" should be replaced with "The above-described".  "(New nodes)" 
> should be replaced with "of new nodes".


ack

> 
>> +
>> +Example::
>> +
>> +	/* SoC DTSI */
>> +
>> +	/ {
>> +		cpus {
>> +			/* ... */
>> +		};
>> +
>> +		psci {
>> +			/* ... */
>> +		};
>> +
>> +		soc@ {
>> +			dma: dma-controller at 10000 {
>> +				/* ... */
>> +			};
>> +
>> +			clk: clock-controller at 80000 {
>> +				/* ... */
>> +			};
>> +		};
>> +	};
>> +
>> +	/* Board DTS - alphabetical order */
>> +
>> +	&clk {
>> +		/* ... */
>> +	};
>> +
>> +	&dma {
>> +		/* ... */
>> +	};
>> +
>> +	/* Board DTS - alternative order, keep as DTSI */
>> +
>> +	&dma {
>> +		/* ... */
>> +	};
>> +
>> +	&clk {
>> +		/* ... */
>> +	};
>> +
>> +Order of Properties in Device Node
>> +----------------------------------
>> +
>> +Following order of properties in device nodes is preferred:
> 
> "Following" should be replaced with "The following".

ack

> 
>> +
>> +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.
>> +
>> +Above order follows approach:
> 
> The last sentence should be replaced with "The above-described ordering 
> follows this approach:".

ack

> 
>> +
>> +1. Most important properties start the node: compatible then bus 
>> addressing to
>> +   match unit address.
>> +2. Each node will have common properties in similar place.
>> +3. Status is the last information to annotate that device node is or 
>> is not
>> +   finished (board resources are needed).
>> +
>> +Example::
>> +
>> +	/* SoC DTSI */
>> +
>> +	device_node: device-class at 6789abc {
>> +		compatible = "vendor,device";
>> +		reg = <0x0 0x06789abc 0x0 0xa123>;
>> +		ranges = <0x0 0x0 0x06789abc 0x1000>;
>> +		#dma-cells = <1>;
>> +		clocks = <&clock_controller 0>, <&clock_controller 1>;
>> +		clock-names = "bus", "host";
>> +		vendor,custom-property = <2>;
>> +		status = "disabled";
>> +
>> +		child_node: child-class at 100 {
>> +			reg = <0x100 0x200>;
>> +			/* ... */
>> +		};
>> +	};
>> +
>> +	/* Board DTS */
>> +
>> +	&device_node {
>> +		vdd-supply = <&board_vreg1>;
>> +		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)
>> +   shall be enclosed in <>.
> 
> The "(e.g. ...)" form should be replaced with ", e.g. ...,".

ack

> 
>> +
>> +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 shall be organized in a way representing the 
>> common
>> +(and re-usable) parts of the hardware.  Typically this means 
>> organizing DTSI
> 
> The "(and re-usable)" form should be replaced with ", reusable".  "The 
> hardware" should be replaced with "hardware".  A comma should be added 
> after "Typically".

ack

> 
>> +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.
> 
> The "(...)" forms should be replaced with ", ...".  Periods at the ends 
> of list items should be deleted, because those aren't real, complete 
> sentences.

ack

> 
>> +
>> +Hardware components which are present on the board shall be placed in 
>> the
> 
> "Which" should be replaced with "that".

ack

> 
>> +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
> 
> "SoC-input" should be replaced with "SoC input".

ack, thanks!

Best regards,
Krzysztof