fdc: change auto fallback drive for ISA FDC to 288

The 2.88 drive is more suitable as a default because
it can still read 1.44 images correctly, but the reverse
is not true.

Since there exist virtio-win drivers that are shipped on
2.88 floppy images, this patch will allow VMs booted without
a floppy disk inserted to later insert a 2.88MB floppy and
have that work.

This patch has been tested with msdos, freedos, fedora,
windows 8 and windows 10 without issue: if problems do
arise for certain guests being unable to cope with 2.88MB
drives as the default, they are in the minority and can use
type=144 as needed (or insert a proper boot medium and omit
type=144/288 or use type=auto) to obtain different drive types.

As icing, the default will remain auto/144 for any pre-2.6
machine types, hopefully minimizing the impact of this change
in legacy hw to basically zero.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1453495865-9649-13-git-send-email-jsnow@redhat.com

hw/block/fdc.c

@@ -2543,7 +2543,7 @@ static Property isa_fdc_properties[] = {
                         FLOPPY_DRIVE_TYPE_AUTO, qdev_prop_fdc_drive_type,
                         FloppyDriveType),
     DEFINE_PROP_DEFAULT("fallback", FDCtrlISABus, state.fallback,
-                        FLOPPY_DRIVE_TYPE_144, qdev_prop_fdc_drive_type,
+                        FLOPPY_DRIVE_TYPE_288, qdev_prop_fdc_drive_type,
                         FloppyDriveType),
     DEFINE_PROP_END_OF_LIST(),
 };

include/hw/compat.h

@@ -3,6 +3,10 @@
 
 #define HW_COMPAT_2_5 \
     {\
+        .driver   = "isa-fdc",\
+        .property = "fallback",\
+        .value    = "144",\
+    },{\
         .driver   = "pvscsi",\
         .property = "x-old-pci-configuration",\
         .value    = "on",\