i386/pc_q35: don't insist on board FDC if there's no default floppy

The "no_floppy = 1" machine class setting causes "default_floppy" in
main() to become zero. Consequently, default_drive() will not call
drive_add() and drive_new() for IF_FLOPPY, index=0, meaning that no
default floppy drive will be created for the virtual machine. In that
case, board code should also not insist on the creation of the
board-default FDC.

The board-default FDC will still be created if the user requests a floppy
drive with "-drive if=floppy".

Additionally, separate FDCs can be specified manually with "-device
isa-fdc". They allow the

  -device isa-fdc,driveA=...

syntax that is more flexible than the one required by the board-default
FDC:

  -global isa-fdc.driveA=...

This patch doesn't change the behavior observably, as all Q35 machine
types have "no_floppy = 0".

Cc: Markus Armbruster <armbru@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: "Gabriel L. Somlo" <gsomlo@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-block@nongnu.org
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>

hw/i386/pc_q35.c

@@ -89,6 +89,7 @@ static void pc_q35_init(MachineState *machine)
     PcGuestInfo *guest_info;
     ram_addr_t lowmem;
     DriveInfo *hd[MAX_SATA_PORTS];
+    MachineClass *mc = MACHINE_GET_CLASS(machine);
 
     /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory
      * and 256 Mbytes for PCI Express Enhanced Configuration Access Mapping
@@ -163,7 +164,6 @@ static void pc_q35_init(MachineState *machine)
     guest_info->legacy_acpi_table_size = 0;
 
     if (smbios_defaults) {
-        MachineClass *mc = MACHINE_GET_CLASS(machine);
         /* These values are guest ABI, do not change */
         smbios_set_defaults("QEMU", "Standard PC (Q35 + ICH9, 2009)",
                             mc->name, smbios_legacy_mode, smbios_uuid_encoded);
@@ -250,7 +250,7 @@ static void pc_q35_init(MachineState *machine)
     }
 
     /* init basic PC hardware */
-    pc_basic_device_init(isa_bus, gsi, &rtc_state, true, &floppy,
+    pc_basic_device_init(isa_bus, gsi, &rtc_state, !mc->no_floppy, &floppy,
                          (pc_machine->vmport != ON_OFF_AUTO_ON), 0xff0104);
 
     /* connect pm stuff to lpc */