Re: [PATCH v3 2/3] RISC-V: uapi: add HWCAP for Bitmanip/Scalar Crypto

[Samuel Ortiz]

On Mon, Jun 13, 2022 at 02:46:35AM +0800, Hongren (Zenithal) Zheng wrote:
> diff --git a/arch/riscv/include/uapi/asm/hwcap.h b/arch/riscv/include/uapi/asm/hwcap.h
> index 46dc3f5ee99f..bfed3e5c338c 100644
> --- a/arch/riscv/include/uapi/asm/hwcap.h
> +++ b/arch/riscv/include/uapi/asm/hwcap.h
> @@ -22,4 +22,26 @@
>  #define COMPAT_HWCAP_ISA_D	(1 << ('D' - 'A'))
>  #define COMPAT_HWCAP_ISA_C	(1 << ('C' - 'A'))
>  
> +/*
> + * HWCAP2 flags - for elf_hwcap2 (in kernel) and AT_HWCAP2
> + *
> + * As only 32 bits of elf_hwcap (in kernel) could be used
> + * and RISC-V has reserved 26 bits of it, other caps like
> + * bitmanip and crypto can not be placed in AT_HWCAP
> + */

Have we agreed that multi-letter ISA extensions would use hwcap to be
exposed to userspace? With so many potential extensions, we could
quickly run out of space on AT_HWCAP2 as well.

Cheers,
Samuel.