Re: [PATCH v2 1/2] hw/i386/postcard.c: New ISA POST card device

[Paolo Bonzini <pbonzini@redhat.com>]

On 7/7/22 02:37, Lev Kujawski wrote:
> @@ -1139,12 +1120,10 @@ void pc_basic_device_init(struct PCMachineState *pcms,
>      qemu_irq pit_alt_irq = NULL;
>      qemu_irq rtc_irq = NULL;
>      ISADevice *pit = NULL;
> -    MemoryRegion *ioport80_io = g_new(MemoryRegion, 1);
>      MemoryRegion *ioportF0_io = g_new(MemoryRegion, 1);
>      X86MachineState *x86ms = X86_MACHINE(pcms);
>  
> -    memory_region_init_io(ioport80_io, NULL, &ioport80_io_ops, NULL, "ioport80", 1);
> -    memory_region_add_subregion(isa_bus->address_space_io, 0x80, ioport80_io);
> +    (void)post_card_init(isa_bus, POST_CARD_PORT_DEFAULT);
>  

This unfortunately breaks live migration of old machine types (new QEMU 
to old QEMU).

The simplest (though not very simple) way to do it is to add a new 
property to the machine (e.g. "postcard-rw") and keep the old 
ioport80_io_ops if the property is false.  Default the property to true, 
and in hw/i386/pc.c make the property false with an entry like

   { TYPE_PC_MACHINE "postcard-rw", "off" },

in pc_compat_7_1.

> +        VMSTATE_UINT16(port, POSTCardState),

port doesn't have to be stored.

Paolo