Re: [PATCH] target/riscv: rvv: Minimum VLEN needs to respect V/Zve extensions

[Max Chou <max.chou@sifive.com>]

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Hi Daniel,

Thanks for the question.
Yes, you are right.
And I find that I miss some patches for the part that you mentioned here.
I'll update this patchset for it.

Thanks,
Max


On Wed, Jul 2, 2025 at 10:48 PM Daniel Henrique Barboza <
dbarboza@ventanamicro.com> wrote:

>
>
> On 6/27/25 10:21 AM, Max Chou wrote:
> > According to the RISC-V instruction set manual, the minimum VLEN needs
> > to respect the following extensions:
> >
> >    Extension     Minimum VLEN
> > * V             128
> > * Zve64[d|f|x]   64
> > * Zve32[f|x]     32
> >
> > Signed-off-by: Max Chou <max.chou@sifive.com>
> > ---
> >   target/riscv/tcg/tcg-cpu.c | 13 +++++++++++--
> >   1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> > index 163e7ce3642..187534009dd 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;
> > +    }
>
> At this moment this is how we're calling riscv_cpu_validate_v():
>
>      if (riscv_has_ext(env, RVV)) {
>          riscv_cpu_validate_v(env, &cpu->cfg, &local_err);
>          if (local_err != NULL) {
>              error_propagate(errp, local_err);
>              return;
>          }
>      }
>
>
> riscv_has_ext(env, RVV) is always true inside the function. The code above
> will
> always result in min_vlen = 128 because of the 'else if' chaining.
>
> IIUC the idea of the patch, what you want is something like:
>
> > +    uint32_t min_vlen = 128;
> >       uint32_t vlen = cfg->vlenb << 3;
> >
> > -    if (vlen > RV_VLEN_MAX || vlen < 128) {
> > +    if (cfg->ext_zve64x) {
> > +        min_vlen = 64;
> > +    } else if (cfg->ext_zve32x) {
> > +        min_vlen = 32;
> > +    }
>
> I.e. init min_vlen to 128 (since RVV is always true) and then change it
> according to
> zve64x and zve32x.
>
>
> Thanks,
>
> Daniel
>
>
>
> > +
> > +    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;
> >       }
> >
>
>

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