target/arm: Allow M-profile CPUs to disable the DSP extension via CPU property

Allow the DSP extension to be disabled via a CPU property for
M-profile CPUs. (A and R-profile CPUs don't have this extension
as a defined separate optional architecture extension, so
they don't need the property.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20190517174046.11146-3-peter.maydell@linaro.org

target/arm/cpu.c

@@ -769,6 +769,9 @@ static Property arm_cpu_has_vfp_property =
 static Property arm_cpu_has_neon_property =
             DEFINE_PROP_BOOL("neon", ARMCPU, has_neon, true);
 
+static Property arm_cpu_has_dsp_property =
+            DEFINE_PROP_BOOL("dsp", ARMCPU, has_dsp, true);
+
 static Property arm_cpu_has_mpu_property =
             DEFINE_PROP_BOOL("has-mpu", ARMCPU, has_mpu, true);
 
@@ -881,6 +884,12 @@ void arm_cpu_post_init(Object *obj)
         }
     }
 
+    if (arm_feature(&cpu->env, ARM_FEATURE_M) &&
+        arm_feature(&cpu->env, ARM_FEATURE_THUMB_DSP)) {
+        qdev_property_add_static(DEVICE(obj), &arm_cpu_has_dsp_property,
+                                 &error_abort);
+    }
+
     if (arm_feature(&cpu->env, ARM_FEATURE_PMSA)) {
         qdev_property_add_static(DEVICE(obj), &arm_cpu_has_mpu_property,
                                  &error_abort);
@@ -1100,6 +1109,26 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         cpu->isar.mvfr0 = u;
     }
 
+    if (arm_feature(env, ARM_FEATURE_M) && !cpu->has_dsp) {
+        uint32_t u;
+
+        unset_feature(env, ARM_FEATURE_THUMB_DSP);
+
+        u = cpu->isar.id_isar1;
+        u = FIELD_DP32(u, ID_ISAR1, EXTEND, 1);
+        cpu->isar.id_isar1 = u;
+
+        u = cpu->isar.id_isar2;
+        u = FIELD_DP32(u, ID_ISAR2, MULTU, 1);
+        u = FIELD_DP32(u, ID_ISAR2, MULTS, 1);
+        cpu->isar.id_isar2 = u;
+
+        u = cpu->isar.id_isar3;
+        u = FIELD_DP32(u, ID_ISAR3, SIMD, 1);
+        u = FIELD_DP32(u, ID_ISAR3, SATURATE, 0);
+        cpu->isar.id_isar3 = u;
+    }
+
     /* Some features automatically imply others: */
     if (arm_feature(env, ARM_FEATURE_V8)) {
         if (arm_feature(env, ARM_FEATURE_M)) {

target/arm/cpu.h

@@ -790,6 +790,8 @@ struct ARMCPU {
     bool has_vfp;
     /* CPU has Neon */
     bool has_neon;
+    /* CPU has M-profile DSP extension */
+    bool has_dsp;
 
     /* CPU has memory protection unit */
     bool has_mpu;