Re: [PATCH RFC v3 2/9] dt-bindings: board: Introduce board-id

[Conor Dooley <conor@kernel.org>]

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On Wed, May 22, 2024 at 04:54:23PM -0700, Elliot Berman wrote:
> Device manufcturers frequently ship multiple boards or SKUs under a
> single softwre package. These software packages ship multiple devicetree
> blobs and require some mechanims to pick the correct DTB for the boards
> that use the software package. This patch introduces a common language
> for adding board identifiers to devicetrees.
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
>  .../devicetree/bindings/board/board-id.yaml        | 71 ++++++++++++++++++++++
>  1 file changed, 71 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/board/board-id.yaml b/Documentation/devicetree/bindings/board/board-id.yaml
> new file mode 100644
> index 000000000000..894c1e310cbd
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/board/board-id.yaml
> @@ -0,0 +1,71 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/board/board-id.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Board identifiers
> +description: |
> +  This node contains a list of identifier values for the board(s) supported by
> +  this devicetree. Identifier values are either N-tuples of integers or a
> +  string. The number of items for an N-tuple identifer is determined by the
> +  property name. String identifiers must be suffixed with "-string".
> +
> +  Every identifier in the devicetree must have a matching value from the board
> +  to be considered a valid devicetree for the board. In other words: if
> +  multiple identifiers are present in the board-id and one identifier doesn't
> +  match against the board, then the devicetree is not applicable. Note this is
> +  not the case where the the board can provide more identifiers than the
> +  devicetree describes: those additional identifers can be ignored.
> +
> +  Identifiers in the devicetree can describe multiple possible valid values,
> +  such as revision 1 and revision 2.
> +
> +maintainers:
> +  - Elliot Berman <quic_eberman@quicinc.com>
> +
> +properties:
> +  $nodename:
> +    const: '/'
> +  board-id:


Does this need to be
properties:
  $nodename:
    const: board-id
? That's the pattern I see for all top level nodes.

> +    type: object
> +    patternProperties:
> +      "^.*(?<!-string)$":

At least this regex now actually works :)

> +        $ref: /schemas/types.yaml#/definitions/uint32-matrix
> +        description: |
> +          List of values that match boards this devicetree applies to.
> +          A bootloader checks whether any of the values in this list
> +          match against the board's value.
> +
> +          The number of items per tuple is determined by the property name,
> +          see the vendor-specific board-id bindings.
> +      "^.*-string$":
> +        $ref: /schemas/types.yaml#/definitions/string-array

Your description above doesn't match a string-array, just a single
string. That said I'm far from sold on the "thou shalt have -string"
edict. If every vendor is expected to go and define their own set of
properties (and provide their own callback in your libfdt PoC) there's
little to no reason to inflict property naming on them, AFAICT all that
is gained is a being able to share
	if (string) {
		return fdt_stringlist_contains(prop->data,
					       fdt32_to_cpu(prop->len),
					       data);
	} else {
		// exact data comparison. data_len is the size of each entry
		if (fdt32_to_cpu(prop->len) % data_len || data_len % 4)
			return -FDT_ERR_BADVALUE;

		for (int i = 0; i < fdt32_to_cpu(prop->len); i += data_len) {
			if (!memcmp(&prop->data[i], data, data_len))
				return 1;
		}

		return 0;
	}
in the libfdt PoC? I'd be expecting that a common mechanism would use
the same "callback" for boards shipped by both Qualcomm and
$other_vendor. Every vendor having different properties and only sharing
the board-id node name seems a wee bit like paying lip-service to a
common mechanism to me. What am I missing?

Thanks,
Conor.



> +        description: |
> +          List of strings that match boards this devicetree applies to.
> +          A bootloader checks whether any of the strings in this list
> +          match against the board's string representation.
> +
> +          String-based matching requires properties to be suffixed with
> +          -string so that a bootloader can match values without otherwise
> +          knowing the meaning of the identifier.
> +
> +examples:
> +  - |
> +    / {
> +      #address-cells = <1>;
> +      #size-cells = <1>;
> +      compatible = "example";
> +      board-id {
> +        // this works with any boards where:
> +        // some-hw-id = 1, other-hw-id = 1, some-id-string = "cat"
> +        // some-hw-id = 1, other-hw-id = 1, some-id-string = "kitten"
> +        // some-hw-id = 1, other-hw-id = 2, some-id-string = "cat"
> +        // some-hw-id = 1, other-hw-id = 2, some-id-string = "kitten"
> +        some-hw-id = <1>; // some-hw-id must be "1"
> +        other-hw-id = <1>, <2>; // other-hw-id must be "1" or "2"
> +        some-id-string = "cat", "kitten"; // some-id-string must be "cat" or "kitten"
> +      };
> +    };
> +
> +additionalProperties: true
> 
> -- 
> 2.34.1

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