hw/intc/arm_gicv3: Allow 'revision' property to be set to 4

Now that we have implemented all the GICv4 requirements, relax the
error-checking on the GIC object's 'revision' property to allow a TCG
GIC to be a GICv4, whilst still constraining the KVM GIC to GICv3.

Our 'revision' property doesn't consider the possibility of wanting
to specify the minor version of the GIC -- for instance there is a
GICv3.1 which adds support for extended SPI and PPI ranges, among
other things, and also GICv4.1.  But since the QOM property is
internal to QEMU, not user-facing, we can cross that bridge when we
come to it. Within the GIC implementation itself code generally
checks against the appropriate ID register feature bits, and the
only use of s->revision is for setting those ID register bits.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-39-peter.maydell@linaro.org

hw/intc/arm_gicv3_common.c

@@ -326,12 +326,14 @@ static void arm_gicv3_common_realize(DeviceState *dev, Error **errp)
     GICv3State *s = ARM_GICV3_COMMON(dev);
     int i, rdist_capacity, cpuidx;
 
-    /* revision property is actually reserved and currently used only in order
-     * to keep the interface compatible with GICv2 code, avoiding extra
-     * conditions. However, in future it could be used, for example, if we
-     * implement GICv4.
+    /*
+     * This GIC device supports only revisions 3 and 4. The GICv1/v2
+     * is a separate device.
+     * Note that subclasses of this device may impose further restrictions
+     * on the GIC revision: notably, the in-kernel KVM GIC doesn't
+     * support GICv4.
      */
-    if (s->revision != 3) {
+    if (s->revision != 3 && s->revision != 4) {
         error_setg(errp, "unsupported GIC revision %d", s->revision);
         return;
     }

hw/intc/arm_gicv3_kvm.c

@@ -781,6 +781,11 @@ static void kvm_arm_gicv3_realize(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (s->revision != 3) {
+        error_setg(errp, "unsupported GIC revision %d for in-kernel GIC",
+                   s->revision);
+    }
+
     if (s->security_extn) {
         error_setg(errp, "the in-kernel VGICv3 does not implement the "
                    "security extensions");