[Qemu-devel] [PATCH 1/4] target/arm: Allow VFP and Neon to be disabled via a CPU property

[Peter Maydell <peter.maydell@linaro.org>]

Allow VFP and neon to be disabled via a CPU property. As with
the "pmu" property, we only allow these features to be removed
from CPUs which have it by default, not added to CPUs which
don't have it.

The primary motivation here is to be able to optionally
create Cortex-M33 CPUs with no FPU, but we provide switches
for both VFP and Neon because the two interact:
 * AArch64 can't have one without the other
 * Some ID register fields only change if both are disabled

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/cpu.h |   4 ++
 target/arm/cpu.c | 150 +++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 148 insertions(+), 6 deletions(-)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 733b840a712..778fb293e7c 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -797,6 +797,10 @@ struct ARMCPU {
     bool has_el3;
     /* CPU has PMU (Performance Monitor Unit) */
     bool has_pmu;
+    /* CPU has VFP */
+    bool has_vfp;
+    /* CPU has Neon */
+    bool has_neon;
 
     /* CPU has memory protection unit */
     bool has_mpu;
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 8eee1d8c59a..406fd360a2a 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -763,6 +763,12 @@ static Property arm_cpu_cfgend_property =
 static Property arm_cpu_has_pmu_property =
             DEFINE_PROP_BOOL("pmu", ARMCPU, has_pmu, true);
 
+static Property arm_cpu_has_vfp_property =
+            DEFINE_PROP_BOOL("vfp", ARMCPU, has_vfp, true);
+
+static Property arm_cpu_has_neon_property =
+            DEFINE_PROP_BOOL("neon", ARMCPU, has_neon, true);
+
 static Property arm_cpu_has_mpu_property =
             DEFINE_PROP_BOOL("has-mpu", ARMCPU, has_mpu, true);
 
@@ -803,6 +809,13 @@ void arm_cpu_post_init(Object *obj)
     if (arm_feature(&cpu->env, ARM_FEATURE_M)) {
         set_feature(&cpu->env, ARM_FEATURE_PMSA);
     }
+    /* Similarly for the VFP feature bits */
+    if (arm_feature(&cpu->env, ARM_FEATURE_VFP4)) {
+        set_feature(&cpu->env, ARM_FEATURE_VFP3);
+    }
+    if (arm_feature(&cpu->env, ARM_FEATURE_VFP3)) {
+        set_feature(&cpu->env, ARM_FEATURE_VFP);
+    }
 
     if (arm_feature(&cpu->env, ARM_FEATURE_CBAR) ||
         arm_feature(&cpu->env, ARM_FEATURE_CBAR_RO)) {
@@ -847,6 +860,27 @@ void arm_cpu_post_init(Object *obj)
                                  &error_abort);
     }
 
+    /*
+     * Allow user to turn off VFP and Neon support, but only for TCG --
+     * KVM does not currently allow us to lie to the guest about its
+     * ID/feature registers, so the guest always sees what the host has.
+     */
+    if (arm_feature(&cpu->env, ARM_FEATURE_VFP)) {
+        cpu->has_vfp = true;
+        if (!kvm_enabled()) {
+            qdev_property_add_static(DEVICE(obj), &arm_cpu_has_vfp_property,
+                                     &error_abort);
+        }
+    }
+
+    if (arm_feature(&cpu->env, ARM_FEATURE_NEON)) {
+        cpu->has_neon = true;
+        if (!kvm_enabled()) {
+            qdev_property_add_static(DEVICE(obj), &arm_cpu_has_neon_property,
+                                     &error_abort);
+        }
+    }
+
     if (arm_feature(&cpu->env, ARM_FEATURE_PMSA)) {
         qdev_property_add_static(DEVICE(obj), &arm_cpu_has_mpu_property,
                                  &error_abort);
@@ -956,6 +990,116 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (arm_feature(env, ARM_FEATURE_AARCH64) &&
+        cpu->has_vfp != cpu->has_neon) {
+        /*
+         * This is an architectural requirement for AArch64; AArch32 is
+         * more flexible and permits VFP-no-Neon and Neon-no-VFP.
+         */
+        error_setg(errp,
+                   "AArch64 CPUs must have both VFP and Neon or neither");
+        return;
+    }
+
+    if (!cpu->has_vfp) {
+        uint64_t t;
+        uint32_t u;
+
+        unset_feature(env, ARM_FEATURE_VFP);
+        unset_feature(env, ARM_FEATURE_VFP3);
+        unset_feature(env, ARM_FEATURE_VFP4);
+
+        t = cpu->isar.id_aa64isar1;
+        t = FIELD_DP64(t, ID_AA64ISAR1, JSCVT, 0);
+        cpu->isar.id_aa64isar1 = t;
+
+        t = cpu->isar.id_aa64pfr0;
+        t = FIELD_DP64(t, ID_AA64PFR0, FP, 0xf);
+        cpu->isar.id_aa64pfr0 = t;
+
+        u = cpu->isar.id_isar6;
+        u = FIELD_DP32(u, ID_ISAR6, JSCVT, 0);
+        cpu->isar.id_isar6 = u;
+
+        u = cpu->isar.mvfr0;
+        u = FIELD_DP32(u, MVFR0, FPSP, 0);
+        u = FIELD_DP32(u, MVFR0, FPDP, 0);
+        u = FIELD_DP32(u, MVFR0, FPTRAP, 0);
+        u = FIELD_DP32(u, MVFR0, FPDIVIDE, 0);
+        u = FIELD_DP32(u, MVFR0, FPSQRT, 0);
+        u = FIELD_DP32(u, MVFR0, FPSHVEC, 0);
+        u = FIELD_DP32(u, MVFR0, FPROUND, 0);
+        cpu->isar.mvfr0 = u;
+
+        u = cpu->isar.mvfr1;
+        u = FIELD_DP32(u, MVFR1, FPFTZ, 0);
+        u = FIELD_DP32(u, MVFR1, FPDNAN, 0);
+        u = FIELD_DP32(u, MVFR1, FPHP, 0);
+        cpu->isar.mvfr1 = u;
+
+        u = cpu->isar.mvfr2;
+        u = FIELD_DP32(u, MVFR2, FPMISC, 0);
+        cpu->isar.mvfr2 = u;
+    }
+
+    if (!cpu->has_neon) {
+        uint64_t t;
+        uint32_t u;
+
+        unset_feature(env, ARM_FEATURE_NEON);
+
+        t = cpu->isar.id_aa64isar0;
+        t = FIELD_DP64(t, ID_AA64ISAR0, DP, 0);
+        cpu->isar.id_aa64isar0 = t;
+
+        t = cpu->isar.id_aa64isar1;
+        t = FIELD_DP64(t, ID_AA64ISAR1, FCMA, 0);
+        cpu->isar.id_aa64isar1 = t;
+
+        t = cpu->isar.id_aa64pfr0;
+        t = FIELD_DP64(t, ID_AA64PFR0, ADVSIMD, 0xf);
+        cpu->isar.id_aa64pfr0 = t;
+
+        u = cpu->isar.id_isar5;
+        u = FIELD_DP32(u, ID_ISAR5, RDM, 0);
+        u = FIELD_DP32(u, ID_ISAR5, VCMA, 0);
+        cpu->isar.id_isar5 = u;
+
+        u = cpu->isar.id_isar6;
+        u = FIELD_DP32(u, ID_ISAR6, DP, 0);
+        u = FIELD_DP32(u, ID_ISAR6, FHM, 0);
+        cpu->isar.id_isar6 = u;
+
+        u = cpu->isar.mvfr1;
+        u = FIELD_DP32(u, MVFR1, SIMDLS, 0);
+        u = FIELD_DP32(u, MVFR1, SIMDINT, 0);
+        u = FIELD_DP32(u, MVFR1, SIMDSP, 0);
+        u = FIELD_DP32(u, MVFR1, SIMDHP, 0);
+        u = FIELD_DP32(u, MVFR1, SIMDFMAC, 0);
+        cpu->isar.mvfr1 = u;
+
+        u = cpu->isar.mvfr2;
+        u = FIELD_DP32(u, MVFR2, SIMDMISC, 0);
+        cpu->isar.mvfr2 = u;
+    }
+
+    if (!cpu->has_neon && !cpu->has_vfp) {
+        uint64_t t;
+        uint32_t u;
+
+        t = cpu->isar.id_aa64isar0;
+        t = FIELD_DP64(t, ID_AA64ISAR0, FHM, 0);
+        cpu->isar.id_aa64isar0 = t;
+
+        t = cpu->isar.id_aa64isar1;
+        t = FIELD_DP64(t, ID_AA64ISAR1, FRINTTS, 0);
+        cpu->isar.id_aa64isar1 = t;
+
+        u = cpu->isar.mvfr0;
+        u = FIELD_DP32(u, MVFR0, SIMDREG, 0);
+        cpu->isar.mvfr0 = u;
+    }
+
     /* Some features automatically imply others: */
     if (arm_feature(env, ARM_FEATURE_V8)) {
         if (arm_feature(env, ARM_FEATURE_M)) {
@@ -1016,12 +1160,6 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
     if (arm_feature(env, ARM_FEATURE_V5)) {
         set_feature(env, ARM_FEATURE_V4T);
     }
-    if (arm_feature(env, ARM_FEATURE_VFP4)) {
-        set_feature(env, ARM_FEATURE_VFP3);
-    }
-    if (arm_feature(env, ARM_FEATURE_VFP3)) {
-        set_feature(env, ARM_FEATURE_VFP);
-    }
     if (arm_feature(env, ARM_FEATURE_LPAE)) {
         set_feature(env, ARM_FEATURE_V7MP);
         set_feature(env, ARM_FEATURE_PXN);
-- 
2.20.1