[RFC PATCH v1 04/11] riscv: Add B to hwcap

[Conor Dooley]

On Fri, Mar 06, 2026 at 12:27:50PM -0600, Andrew Jones wrote:
> On Fri, Mar 06, 2026 at 10:17:19AM +0800, Guodong Xu wrote:

> > + /*
> > +  * B is functionally a bundle (Zba + Zbb + Zbs,
> > +  * no additional instructions). We use SUPERSET
> > +  * instead of BUNDLE because B needs a valid ext
> > +  * id for isa2hwcap[] to set COMPAT_HWCAP_ISA_B.

What's the actual rationale for it working like that?
Why shouldn't bundles appear in cpuinfo etc, I forget entirely why we
did it this way. Feels like it'd be easier for users, no?

2023 me might disagree, but 2026 me doesn't see the value in hiding these
extensions. All I can think of was me being very negative, and hedging
against bad software checking for zkn and not checking for the subsets,
and breaking if the dt listed the entire subset but not zkn. That, or
not wanting to implement code that looked for subset extensions and
populated the relevant bundle if the bundle itself was missing but all
components were there.
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