Re: [PATCH v2 2/2] target/riscv: rvv: Modify minimum VLEN according to enabled vector extensions

[Alistair Francis <alistair23@gmail.com>]

On Tue, Sep 23, 2025 at 7:08 PM Max Chou <max.chou@sifive.com> wrote:
>
> According to the RISC-V unprivileged specification, the VLEN should be greater
> or equal to the ELEN. This commit modifies the minimum VLEN based on the vector
> extensions and introduces a check rule for VLEN and ELEN.
>
>   Extension     Minimum VLEN
> * V                      128
> * Zve64[d|f|x]            64
> * Zve32[f|x]              32
>
> Signed-off-by: Max Chou <max.chou@sifive.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/tcg/tcg-cpu.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index a6f60f55ceb..02d99bb0ae9 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -416,12 +416,21 @@ static void riscv_cpu_validate_misa_priv(CPURISCVState *env, Error **errp)
>  static void riscv_cpu_validate_v(CPURISCVState *env, RISCVCPUConfig *cfg,
>                                   Error **errp)
>  {
> +    uint32_t min_vlen;
>      uint32_t vlen = cfg->vlenb << 3;
>
> -    if (vlen > RV_VLEN_MAX || vlen < 128) {
> +    if (riscv_has_ext(env, RVV)) {
> +        min_vlen = 128;
> +    } else if (cfg->ext_zve64x) {
> +        min_vlen = 64;
> +    } else if (cfg->ext_zve32x) {
> +        min_vlen = 32;
> +    }
> +
> +    if (vlen > RV_VLEN_MAX || vlen < min_vlen) {
>          error_setg(errp,
>                     "Vector extension implementation only supports VLEN "
> -                   "in the range [128, %d]", RV_VLEN_MAX);
> +                   "in the range [%d, %d]", min_vlen, RV_VLEN_MAX);
>          return;
>      }
>
> @@ -431,6 +440,12 @@ static void riscv_cpu_validate_v(CPURISCVState *env, RISCVCPUConfig *cfg,
>                     "in the range [8, 64]");
>          return;
>      }
> +
> +    if (vlen < cfg->elen) {
> +        error_setg(errp, "Vector extension implementation requires VLEN "
> +                         "to be greater than or equal to ELEN");
> +        return;
> +    }
>  }
>
>  static void riscv_cpu_disable_priv_spec_isa_exts(RISCVCPU *cpu)
> --
> 2.43.0
>
>