target/arm: Allow users to set the number of VFP registers

Cortex A7 CPUs with an FPU implementing VFPv4 without NEON support
have 16 64-bit FPU registers and not 32 registers. Let users set the
number of VFP registers with a CPU property.

The primary use case of this property is for the Cortex A7 of the
Aspeed AST2600 SoC.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/arm/aspeed_ast2600.c

@@ -316,6 +316,8 @@ static void aspeed_soc_ast2600_realize(DeviceState *dev, Error **errp)
                                 &error_abort);
         object_property_set_bool(OBJECT(&s->cpu[i]), "neon", false,
                                 &error_abort);
+        object_property_set_bool(OBJECT(&s->cpu[i]), "vfp-d32", false,
+                                &error_abort);
         object_property_set_link(OBJECT(&s->cpu[i]), "memory",
                                  OBJECT(s->memory), &error_abort);
 

target/arm/cpu.c

@@ -1277,6 +1277,9 @@ static Property arm_cpu_cfgend_property =
 static Property arm_cpu_has_vfp_property =
             DEFINE_PROP_BOOL("vfp", ARMCPU, has_vfp, true);
 
+static Property arm_cpu_has_vfp_d32_property =
+            DEFINE_PROP_BOOL("vfp-d32", ARMCPU, has_vfp_d32, true);
+
 static Property arm_cpu_has_neon_property =
             DEFINE_PROP_BOOL("neon", ARMCPU, has_neon, true);
 
@@ -1408,6 +1411,22 @@ void arm_cpu_post_init(Object *obj)
         }
     }
 
+    if (cpu->has_vfp && cpu_isar_feature(aa32_simd_r32, cpu)) {
+        cpu->has_vfp_d32 = true;
+        if (!kvm_enabled()) {
+            /*
+             * The permitted values of the SIMDReg bits [3:0] on
+             * Armv8-A are either 0b0000 and 0b0010. On such CPUs,
+             * make sure that has_vfp_d32 can not be set to false.
+             */
+            if (!(arm_feature(&cpu->env, ARM_FEATURE_V8) &&
+                  !arm_feature(&cpu->env, ARM_FEATURE_M))) {
+                qdev_property_add_static(DEVICE(obj),
+                                         &arm_cpu_has_vfp_d32_property);
+            }
+        }
+    }
+
     if (arm_feature(&cpu->env, ARM_FEATURE_NEON)) {
         cpu->has_neon = true;
         if (!kvm_enabled()) {
@@ -1674,6 +1693,19 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (cpu->has_vfp_d32 != cpu->has_neon) {
+        error_setg(errp, "ARM CPUs must have both VFP-D32 and Neon or neither");
+        return;
+    }
+
+   if (!cpu->has_vfp_d32) {
+        uint32_t u;
+
+        u = cpu->isar.mvfr0;
+        u = FIELD_DP32(u, MVFR0, SIMDREG, 1); /* 16 registers */
+        cpu->isar.mvfr0 = u;
+    }
+
     if (!cpu->has_vfp) {
         uint64_t t;
         uint32_t u;

target/arm/cpu.h

@@ -924,6 +924,8 @@ struct ArchCPU {
     bool has_pmu;
     /* CPU has VFP */
     bool has_vfp;
+    /* CPU has 32 VFP registers */
+    bool has_vfp_d32;
     /* CPU has Neon */
     bool has_neon;
     /* CPU has M-profile DSP extension */