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

22 May 2024

Hi Conor,
Thanks for taking the time to look at the patch.
On Tue, May 21, 2024 at 08:21:45PM +0100, Conor Dooley wrote:
...
On Tue, May 21, 2024 at 11:37:59AM -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.
Okay, you've got the problem statement here, nice.
...
This patch introduces a common language
for adding board identifiers to devicetrees.
But then a completely useless remainder of the commit message.
I open this patch, see the regexes, say "wtf", look at the commit
message and there is absolutely no explanation of what these properties
are for. That's quite frankly just not good enough - even for an RFC.
Understood, I've been trying to walk the line of getting the idea across
to have conversation about the board-ids, while not getting into too
much of the weeds. I was hoping the example and the matching code in the
first patch would get enough of the idea across, but I totally
empathize that might not be enough. I'll reply here shortly with a
version of this patch which adds more details.
...
...
Signed-off-by: Elliot Berman quic_eberman@quicinc.com
.../devicetree/bindings/board/board-id.yaml        | 24 ++++++++++++++++++++++
 1 file changed, 24 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..99514aef9718
--- /dev/null
+++ b/Documentation/devicetree/bindings/board/board-id.yaml
@@ -0,0 +1,24 @@
+# SPDX-License-Identifier: 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: Common property for board-id subnode
s/property/properties/
...



+maintainers:


Elliot Berman quic_eberman@quicinc.com




+properties:

$nodename:
const: '/'
board-id:
type: object
patternProperties:
 "^.*(?!_str)$":



Does this regex even work? Take "foo_str" as an example - doesn't "^.*"
consume all of the string, leaving the negative lookahead with nothing
to object to? I didn't properly test this with an example and the dt
tooling, but I lazily threw it into regex101 and both the python and
emcascript versions agree with me. Did you test this?
Right, it should be a lookbehind, not a lookahead.
...
And while I am here, no underscores in property names please. And if
"str" means string, I suggest not saving 3 characters.
...

   $ref: /schemas/types.yaml#/definitions/uint32-matrix


 "^.*_str$":


   $ref: /schemas/types.yaml#/definitions/string-array



Why do we even need two methods? Commit message tells me nothing and
there's no description at all... Why do we need regexes here, rather
than explicitly defined properties? Your commit message should explain
the justification for that and the property descriptions (as comments if
needs be for patternProperties) should explain why this is intended to
be used.
How is anyone supposed to look at this binding and understand how it
should be used?
I was thinking that firmware may only provide the data without being
able to provide the context whether the value is a number or a string.
I think this is posisble if firmware provides the device's board
identifier in the format of a DT itself. It seems natural to me in the
EBBR flow. There is example of this in example in patches 3
(fdt-select-board) and 9 (the test suite). DTB doesn't inherently
provide instruction on how to interpret a property's value, so I created
a rule that strings have to be suffixed with "-string".
One other note -- I (QCOM) don't currently have a need for board-ids to
be strings. I thought it was likely that someone might want that though.
Thanks,
Elliot

    

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

Signed-off-by: Elliot Berman quic_eberman@quicinc.com

Signed-off-by: Elliot Berman quic_eberman@quicinc.com