[PATCH] serial: Fix double migration data

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

After c9808d60281 we have both an object representing the serial-isa
device and a separate object representing the underlying common serial
uart.  Both of these have vmsd's associated with them and thus the
migration stream ends up with two copies of the migration data - the
serial-isa includes the vmstate of the core serial.   Besides
being wrong, it breaks backwards migration compatibility.

Fix this by removing the dc->vmsd from the core device, so it only
gets migrated by any parent devices including it.
Add a vmstate_serial_mm so that any device that uses serial_mm_init
rather than creating a device still gets migrated.
(That doesn't fix backwards migration for serial_mm_init users,
but does seem to work forwards for ppce500).

Fixes: c9808d60281 ('serial: realize the serial device')
Buglink: https://bugs.launchpad.net/qemu/+bug/1869426
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 hw/char/serial.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 2ab8b69e03..c822a9ae6c 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -1043,7 +1043,6 @@ static void serial_class_init(ObjectClass *klass, void* data)
     dc->user_creatable = false;
     dc->realize = serial_realize;
     dc->unrealize = serial_unrealize;
-    dc->vmsd = &vmstate_serial;
     device_class_set_props(dc, serial_properties);
 }
 
@@ -1113,6 +1112,16 @@ static void serial_mm_realize(DeviceState *dev, Error **errp)
     sysbus_init_irq(SYS_BUS_DEVICE(smm), &smm->serial.irq);
 }
 
+static const VMStateDescription vmstate_serial_mm = {
+    .name = "serial",
+    .version_id = 3,
+    .minimum_version_id = 2,
+    .fields = (VMStateField[]) {
+        VMSTATE_STRUCT(serial, SerialMM, 0, vmstate_serial, SerialState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 SerialMM *serial_mm_init(MemoryRegion *address_space,
                          hwaddr base, int regshift,
                          qemu_irq irq, int baudbase,
@@ -1162,6 +1171,7 @@ static void serial_mm_class_init(ObjectClass *oc, void *data)
 
     device_class_set_props(dc, serial_mm_properties);
     dc->realize = serial_mm_realize;
+    dc->vmsd = &vmstate_serial_mm;
 }
 
 static const TypeInfo serial_mm_info = {
-- 
2.25.1