[PATCH v4 06/11] dt-bindings: riscv: Add B ISA extension description

[Conor Dooley]

On Sat, Jan 10, 2026 at 01:18:18PM +0800, Guodong Xu wrote:
> Add description of the single-letter B extension for Bit Manipulation.
> B is mandatory for RVA23U64.
> 
> The B extension is ratified in the 20240411 version of the unprivileged
> ISA specification. According to the ratified spec, the B standard
> extension comprises instructions provided by the Zba, Zbb, and Zbs
> extensions.
> 
> Add two-way dependency check to enforce that B implies Zba/Zbb/Zbs; and
> when Zba/Zbb/Zbs (all of them) are specified, then B must be added too.
> 
> The reason why B/Zba/Zbb/Zbs must coexist at the same time is that
> unlike other single-letter extensions, B was ratified (Apr/2024) much
> later than its component extensions Zba/Zbb/Zbs (Jun/2021).
> 
> When "b" is specified, zba/zbb/zbs must be present to ensure
> backward compatibility with existing software and kernels that only
> look for the explicit component strings.
> 
> When all three components zba/zbb/zbs are specified, "b" should also be
> present. Making "b" mandatory when all three components are present.

> Existing devicetrees with zba/zbb/zbs but without "b" will generate
> warnings that can be fixed in follow-up patches.

Are you going to send these fixup patches for other devicetrees? The
majority appear to be other spacemit devices.
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