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

[Daniel Henrique Barboza]

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.c...@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;
      }