[PATCH v3] docs: dt-bindings: Specify ordering for properties within groups

[Dragan Simic]

When it comes to ordering of the individual properties inside each property
group, applying natural sort order to multi-digit numbers [1] found inside
the property names can result in more logical and more usable property lists,
similarly to what's already the case with the alpha-numerical ordering of
the nodes without unit addresses.

Let's have this clearly specified in the DTS coding style, together with
a brief description of the natural sort order for those readers who aren't
familiar with it already.  Also expand the provided node example a bit, to
actually show the results of applying natural sort order.

Applying strict alpha-numerical ordering can result in property lists that
are suboptimal from the usability standpoint.  For the provided example,
which stems from a real-world DT, [2][3][4] applying strict alpha-numerical
ordering produces the following undesirable result:

  vdd-0v9-supply = <&board_vreg1>;
  vdd-12v-supply = <&board_vreg3>;
  vdd-1v8-supply = <&board_vreg4>;
  vdd-3v3-supply = <&board_vreg2>;

Having the properties sorted in natural order by their associated voltages
is more logical, more usable, and a bit more consistent.

[1] https://en.wikipedia.org/wiki/Natural_sort_order
[2] https://lore.kernel.org/linux-rockchip/b39cfd7490d8194f053bf3971f13a43472d1769e.1740941097.git.dsimic@xxxxxxxxxxx/
[3] https://lore.kernel.org/linux-rockchip/174104113599.8946.16805724674396090918.b4-ty@xxxxxxxxx/
[4] https://lore.kernel.org/linux-rockchip/757afa87255212dfa5abf4c0e31deb08@xxxxxxxxxxx/

Signed-off-by: Dragan Simic <dsimic@xxxxxxxxxxx>
---

Notes:
    Changes in v3:
      - Rewrote the part of the changes that describes natural sort order
        and its relation to "standard" alpha-numerical ordering, to make
        it more understandable, as suggested by Krzysztof [6]
      - Slightly expanded the patch description, to clarify the additional
        goal of explaining the natural sort order briefly
    
    Changes in v2:
      - Changed the additions to the coding style to specify natural sort
        order, which avoids amibguity, as suggested by Krzysztof [5]
      - Adjusted and expanded the patch description appropriately, together
        with including one more reference for the natural sort order
    
    Link to v1: https://lore.kernel.org/linux-kernel/09d6f2fc111b3d6e58987336944f93ec36b65118.1741071107.git.dsimic@xxxxxxxxxxx/T/#u
    Link to v2: https://lore.kernel.org/linux-kernel/47c51c10098f089e52fb14c5c5527611dc8daf32.1741164239.git.dsimic@xxxxxxxxxxx/T/#u
    
    [5] https://lore.kernel.org/linux-kernel/20250305-defiant-serious-newt-b7c5ea@krzk-bin/
    [6] https://lore.kernel.org/linux-kernel/20250306-dexterous-goshawk-of-aptitude-e4f1f6@krzk-bin/

 .../devicetree/bindings/dts-coding-style.rst       | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/dts-coding-style.rst b/Documentation/devicetree/bindings/dts-coding-style.rst
index 8a68331075a0..7d183c1ade74 100644
--- a/Documentation/devicetree/bindings/dts-coding-style.rst
+++ b/Documentation/devicetree/bindings/dts-coding-style.rst
@@ -133,6 +133,15 @@ The above-described ordering follows this approach:
 3. Status is the last information to annotate that device node is or is not
    finished (board resources are needed).
 
+The above-described ordering specifies the preferred ordering of property
+groups, while the individual properties inside each group shall use natural
+sort order by the property name.
+
+The natural sort order differs from alpha-numerical ordering only by treating
+any single- and multi-digit numbers found inside the property names atomically,
+and by taking their actual numerical values and comparing those values between
+themselves to determine the order of property names.
+
 Example::
 
 	/* SoC DTSI */
@@ -158,7 +167,10 @@ Example::
 	/* Board DTS */
 
 	&device_node {
-		vdd-supply = <&board_vreg1>;
+		vdd-0v9-supply = <&board_vreg1>;
+		vdd-1v8-supply = <&board_vreg4>;
+		vdd-3v3-supply = <&board_vreg2>;
+		vdd-12v-supply = <&board_vreg3>;
 		status = "okay";
 	}