Re: [PATCH 1/2] target/riscv: Lower bound of VLEN is 32, and check VLEN >= ELEN

[Weiwei Li]

在 2022/7/8 下午3:39, Kito Cheng 写道:
> According RVV spec 1.0, the minmal requirement of VLEN is great than or
> equal to ELEN, and minmal possible ELEN is 32, and also spec has mention
> `Minimum VLEN` for zve32* is 32, so the lower bound of VLEN is 32 I
> think.
>
> [1] 
> https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#2-implementation-defined-constant-parameters
> [2] 
> https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#182-zve-vector-extensions-for-embedded-processors
>
> Signed-off-by: Kito Cheng <kito.cheng@sifive.com>
> ---
>   target/riscv/cpu.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 1bb3973806..487d0faa63 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -740,10 +740,10 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
> **errp)
>                           "Vector extension VLEN must be power of 2");
>                   return;
>               }
> -            if (cpu->cfg.vlen > RV_VLEN_MAX || cpu->cfg.vlen < 128) {
> +            if (cpu->cfg.vlen > RV_VLEN_MAX || cpu->cfg.vlen < 32) {
>                   error_setg(errp,
>                           "Vector extension implementation only supports VLEN "
> -                        "in the range [128, %d]", RV_VLEN_MAX);
> +                        "in the range [32, %d]", RV_VLEN_MAX);
>                   return;
>               }

The check for "VLEN in the range [128, RV_VLEN_MAX]" seems right here, 
since this check is for

V vector extension in current implementation and  "The V vector 
extension requires Zvl128b"(in section 18.3).

Regards,

Weiwei Li

>               if (!is_power_of_2(cpu->cfg.elen)) {
> @@ -757,6 +757,12 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
> **errp)
>                           "in the range [8, 64]");
>                   return;
>               }
> +            if (cpu->cfg.vlen < cpu->cfg.elen) {
> +                error_setg(errp,
> +                        "Vector extension VLEN must be greater than or equal "
> +                        "to ELEN");
> +                return;
> +            }
>               if (cpu->cfg.vext_spec) {
>                   if (!g_strcmp0(cpu->cfg.vext_spec, "v1.0")) {
>                       vext_version = VEXT_VERSION_1_00_0;