ich9: Document why cannot_instantiate_with_device_add_yet

An ICH9 southbridge contains several PCI devices, some of them with
multiple functions.  We model each function as a separate qdev.  Two
of them need some special wiring set up in pc_q35_init() to work: the
LPC controller at 00:1f.0, and the SMBus controller at 00:1f.3.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

hw/i2c/smbus_ich9.c

@@ -97,11 +97,15 @@ static void ich9_smb_class_init(ObjectClass *klass, void *data)
     k->device_id = PCI_DEVICE_ID_INTEL_ICH9_6;
     k->revision = ICH9_A2_SMB_REVISION;
     k->class_id = PCI_CLASS_SERIAL_SMBUS;
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     dc->vmsd = &vmstate_ich9_smbus;
     dc->desc = "ICH9 SMBUS Bridge";
     k->init = ich9_smbus_initfn;
     k->config_write = ich9_smbus_write_config;
+    /*
+     * Reason: part of ICH9 southbridge, needs to be wired up by
+     * pc_q35_init()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 i2c_bus *ich9_smb_init(PCIBus *bus, int devfn, uint32_t smb_io_base)

hw/isa/lpc_ich9.c

@@ -644,14 +644,17 @@ static void ich9_lpc_class_init(ObjectClass *klass, void *data)
     dc->reset = ich9_lpc_reset;
     k->init = ich9_lpc_initfn;
     dc->vmsd = &vmstate_ich9_lpc;
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     k->config_write = ich9_lpc_config_write;
     dc->desc = "ICH9 LPC bridge";
     k->vendor_id = PCI_VENDOR_ID_INTEL;
     k->device_id = PCI_DEVICE_ID_INTEL_ICH9_8;
     k->revision = ICH9_A2_LPC_REVISION;
     k->class_id = PCI_CLASS_BRIDGE_ISA;
-
+    /*
+     * Reason: part of ICH9 southbridge, needs to be wired up by
+     * pc_q35_init()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo ich9_lpc_info = {