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

[Guodong Xu]

Hi, Conor

On Tue, Jan 13, 2026 at 5:41 AM Conor Dooley <conor at kernel.org> wrote:
>
> 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.

Yes, I will. My check shows that these three dtsi files need to be updated to
include the newly ratified "b" extension:

arch/riscv/boot/dts/anlogic/dr1v90.dtsi
arch/riscv/boot/dts/sophgo/sg2044-cpus.dtsi
arch/riscv/boot/dts/spacemit/k1.dtsi

I will start a follow up patch to update these dtsi files. Basically, adding
"b" into both the "riscv,isa-extensions" and "riscv,isa" (when available)
fields.

Thank you for your review.

Best regards,
Guodong Xu