Commit 0cdb7fc1 authored by Guodong Xu's avatar Guodong Xu Committed by Conor Dooley
Browse files

dt-bindings: riscv: Add B ISA extension description 



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.

Signed-off-by: default avatarGuodong Xu <guodong@riscstar.com>
Signed-off-by: default avatarConor Dooley <conor.dooley@microchip.com>
parent fff010c7

Documentation/devicetree/bindings/riscv/extensions.yaml

+31 −0
Original line number Diff line number Diff line
@@ -109,6 +109,13 @@ properties: 
            The standard C extension for compressed instructions, as ratified in

            the 20191213 version of the unprivileged ISA specification.



        - const: b

          description:

            The standard B extension for bit manipulation instructions, as

            ratified in the 20240411 version of the unprivileged ISA

            specification. The B standard extension comprises instructions

            provided by the Zba, Zbb, and Zbs extensions.



        - const: v

          description:

            The standard V extension for vector operations, as ratified
@@ -738,6 +745,30 @@ properties: 
        then:

          contains:

            const: f

      # B comprises Zba, Zbb, and Zbs

      - if:

          contains:

            const: b

        then:

          allOf:

            - contains:

                const: zba

            - contains:

                const: zbb

            - contains:

                const: zbs

      # Zba, Zbb, Zbs together require B

      - if:

          allOf:

            - contains:

                const: zba

            - contains:

                const: zbb

            - contains:

                const: zbs

        then:

          contains:

            const: b

      # Zcb depends on Zca

      - if:

          contains: