Even after taking RVG off from riscv_cpu_validate_set_extensions(), the
function is still doing too much. It is validating misa bits, then
validating named extensions, and if the validation succeeds it's doing
more changes in both cpu->cfg and MISA bits.

It works for the support we have today, since we'll error out during
realize() time. This is not enough to support write_misa() though - we
don't want to error out if userspace writes something odd in the CSR.

This patch starts splitting riscv_cpu_validate_set_extensions() into a
three step process: validate misa_ext, validate cpu->cfg, then commit
the configuration. This separation will allow us to use these functions
in write_misa() without having to worry about saving CPU state during
runtime because the function changed state but failed to validate.

riscv_cpu_validate_misa_ext() will host all validations related to misa
bits only. Validations using misa bits + name extensions will remain in
validate_set_extensions().

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/cpu.c | 77 ++++++++++++++++++++++++++--------------------
 1 file changed, 43 insertions(+), 34 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 110b52712c..c7b05d7c4e 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1025,6 +1025,43 @@ static void riscv_cpu_disable_priv_spec_isa_exts(RISCVCPU *cpu)
     }
 }
 
+static void riscv_cpu_validate_misa_ext(RISCVCPU *cpu, Error **errp)
+{
+    if (cpu->cfg.ext_i && cpu->cfg.ext_e) {
+        error_setg(errp,
+                   "I and E extensions are incompatible");
+        return;
+    }
+
+    if (!cpu->cfg.ext_i && !cpu->cfg.ext_e) {
+        error_setg(errp,
+                   "Either I or E extension must be set");
+        return;
+    }
+
+    if (cpu->cfg.ext_s && !cpu->cfg.ext_u) {
+        error_setg(errp,
+                   "Setting S extension without U extension is illegal");
+        return;
+    }
+
+    if (cpu->cfg.ext_h && !cpu->cfg.ext_i) {
+        error_setg(errp,
+                   "H depends on an I base integer ISA with 32 x registers");
+        return;
+    }
+
+    if (cpu->cfg.ext_h && !cpu->cfg.ext_s) {
+        error_setg(errp, "H extension implicitly requires S-mode");
+        return;
+    }
+
+    if (cpu->cfg.ext_d && !cpu->cfg.ext_f) {
+        error_setg(errp, "D extension requires F extension");
+        return;
+    }
+}
+
 static void riscv_cpu_validate_misa_mxl(RISCVCPU *cpu, Error **errp)
 {
     RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(cpu);
@@ -1072,35 +1109,6 @@ static void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
         return;
     }
 
-    if (cpu->cfg.ext_i && cpu->cfg.ext_e) {
-        error_setg(errp,
-                   "I and E extensions are incompatible");
-        return;
-    }
-
-    if (!cpu->cfg.ext_i && !cpu->cfg.ext_e) {
-        error_setg(errp,
-                   "Either I or E extension must be set");
-        return;
-    }
-
-    if (cpu->cfg.ext_s && !cpu->cfg.ext_u) {
-        error_setg(errp,
-                   "Setting S extension without U extension is illegal");
-        return;
-    }
-
-    if (cpu->cfg.ext_h && !cpu->cfg.ext_i) {
-        error_setg(errp,
-                   "H depends on an I base integer ISA with 32 x registers");
-        return;
-    }
-
-    if (cpu->cfg.ext_h && !cpu->cfg.ext_s) {
-        error_setg(errp, "H extension implicitly requires S-mode");
-        return;
-    }
-
     if (cpu->cfg.ext_f && !cpu->cfg.ext_icsr) {
         error_setg(errp, "F extension requires Zicsr");
         return;
@@ -1120,11 +1128,6 @@ static void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
         return;
     }
 
-    if (cpu->cfg.ext_d && !cpu->cfg.ext_f) {
-        error_setg(errp, "D extension requires F extension");
-        return;
-    }
-
     /* The V vector extension depends on the Zve64d extension */
     if (cpu->cfg.ext_v) {
         cpu->cfg.ext_zve64d = true;
@@ -1349,6 +1352,12 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         env->misa_ext_mask = env->misa_ext;
     }
 
+    riscv_cpu_validate_misa_ext(cpu, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
     riscv_cpu_validate_set_extensions(cpu, &local_err);
     if (local_err != NULL) {
         error_propagate(errp, local_err);
-- 
2.39.2