Re: [PATCH v8 01/11] riscv: Add B to hwcap and hwprobe

[Guodong Xu <guodong.xu@oss.qualcomm.com>]

Hi Heinrich,

On Mon, 21 Sep 2026 16:24:53 +0200, Heinrich Schuchardt wrote:
> On 9/20/26 09:18, Guodong Xu wrote:
>> [ ... ]
>>   	__RISCV_ISA_EXT_DATA(q, RISCV_ISA_EXT_Q),
>>   	__RISCV_ISA_EXT_SUPERSET(c, RISCV_ISA_EXT_C, riscv_c_exts),
>> +	__RISCV_ISA_EXT_SUPERSET(b, RISCV_ISA_EXT_B, riscv_b_exts),
>
> Hello Guodong,
>
> The RISC-V Unpriviledged ISA specification has this description of 
> extension B:
>
> "The B standard extension comprises instructions provided by the Zba, 
> Zbb, and Zbs extensions."
>
> __RISCV_ISA_EXT_SUPERSET would imply that something else but 
> riscv_b_exts is in B. But such an extra seems not to exist.
>
> So shouldn't __RISCV_ISA_EXT_BUNDLE be used here? Some code further 
> change may be needed to set extension B if riscv_b_exts is fulfilled.

Thanks for the review. Intentional, and the difference between the two
macros is whether the extension gets a bit of its own.

__RISCV_ISA_EXT_BUNDLE carries RISCV_ISA_EXT_INVALID as its id: parsing
the name only sets the bits of its parts. That fits zk, zkn names, which
are shorthands with no identity of their own beyond the ISA string.

B is different: it is a single-letter standard extension with its own
misa bit (in the same way as A), and AT_HWCAP on RISC-V is the bitmask
of exactly those single letters, so the kernel needs a bit for B itself.

A is declared the same way; with the spec defines A in the same words as
B. If I can take that as a precedence.

IMHO, "superset" in this table means "also sets these subset bits", not
"contains something extra".

Guodong