- 'q35' machine type already explicitly forbids fallback
- 'isapc' never supported USB and '-usb' is ignored
- 'i440fx' does support '-usb' and translates it into 'piix3-uhci' which
is identical to what libvirt selects
- we currently don't care about 'microvm'
Attempting to start an 'pc' (i440fx) machine with -usb when 'piix3-uhci'
is compiled out will fail and in any other case libvirt will use the
proper explicitly selected controller.
Drop the '-usb' downgrade for x86 arch.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
