diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
index c29a703..368a76b 100644
--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -508,9 +508,13 @@ static void piix4_pm_class_init(ObjectClass *klass, void *data)
     k->revision = 0x03;
     k->class_id = PCI_CLASS_BRIDGE_OTHER;
     dc->desc = "PM";
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     dc->vmsd = &vmstate_acpi;
     dc->props = piix4_pm_properties;
+    /*
+     * Reason: part of PIIX4 southbridge, needs to be wired up,
+     * e.g. by mips_malta_init()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo piix4_pm_info = {
diff --git a/hw/ide/piix.c b/hw/ide/piix.c
index 27b08e1..9b5960b 100644
--- a/hw/ide/piix.c
+++ b/hw/ide/piix.c
@@ -248,7 +248,6 @@ static void piix3_ide_class_init(ObjectClass *klass, void *data)
     k->device_id = PCI_DEVICE_ID_INTEL_82371SB_1;
     k->class_id = PCI_CLASS_STORAGE_IDE;
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
 }
 
 static const TypeInfo piix3_ide_info = {
@@ -267,7 +266,6 @@ static void piix3_ide_xen_class_init(ObjectClass *klass, void *data)
     k->device_id = PCI_DEVICE_ID_INTEL_82371SB_1;
     k->class_id = PCI_CLASS_STORAGE_IDE;
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     dc->unplug = pci_piix3_xen_ide_unplug;
 }
 
@@ -289,7 +287,6 @@ static void piix4_ide_class_init(ObjectClass *klass, void *data)
     k->device_id = PCI_DEVICE_ID_INTEL_82371AB;
     k->class_id = PCI_CLASS_STORAGE_IDE;
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
 }
 
 static const TypeInfo piix4_ide_info = {
diff --git a/hw/isa/piix4.c b/hw/isa/piix4.c
index d9dac61..def6fe3 100644
--- a/hw/isa/piix4.c
+++ b/hw/isa/piix4.c
@@ -113,8 +113,12 @@ static void piix4_class_init(ObjectClass *klass, void *data)
     k->device_id = PCI_DEVICE_ID_INTEL_82371AB_0;
     k->class_id = PCI_CLASS_BRIDGE_ISA;
     dc->desc = "ISA bridge";
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     dc->vmsd = &vmstate_piix4;
+    /*
+     * Reason: part of PIIX4 southbridge, needs to be wired up,
+     * e.g. by mips_malta_init()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo piix4_info = {
diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
index 8089fd6..1526fd4 100644
--- a/hw/pci-host/piix.c
+++ b/hw/pci-host/piix.c
@@ -644,7 +644,6 @@ static void piix3_class_init(ObjectClass *klass, void *data)
 
     dc->desc        = "ISA bridge";
     dc->vmsd        = &vmstate_piix3;
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     k->no_hotplug   = 1;
     k->init         = piix3_initfn;
     k->config_write = piix3_write_config;
@@ -652,6 +651,11 @@ static void piix3_class_init(ObjectClass *klass, void *data)
     /* 82371SB PIIX3 PCI-to-ISA bridge (Step A1) */
     k->device_id    = PCI_DEVICE_ID_INTEL_82371SB_0;
     k->class_id     = PCI_CLASS_BRIDGE_ISA;
+    /*
+     * Reason: part of PIIX3 southbridge, needs to be wired up by
+     * pc_piix.c's pc_init1()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo piix3_info = {
@@ -668,7 +672,6 @@ static void piix3_xen_class_init(ObjectClass *klass, void *data)
 
     dc->desc        = "ISA bridge";
     dc->vmsd        = &vmstate_piix3;
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     k->no_hotplug   = 1;
     k->init         = piix3_initfn;
     k->config_write = piix3_write_config_xen;
@@ -676,6 +679,11 @@ static void piix3_xen_class_init(ObjectClass *klass, void *data)
     /* 82371SB PIIX3 PCI-to-ISA bridge (Step A1) */
     k->device_id    = PCI_DEVICE_ID_INTEL_82371SB_0;
     k->class_id     = PCI_CLASS_BRIDGE_ISA;
+    /*
+     * Reason: part of PIIX3 southbridge, needs to be wired up by
+     * pc_piix.c's pc_init1()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 };
 
 static const TypeInfo piix3_xen_info = {
