Re: [Qemu-devel] KVM call minutes 2013-01-29 - Port I/O

[Anthony Liguori <anthony@codemonkey.ws>]

Gerd Hoffmann <kraxel@redhat.com> writes:

>   Hi,
>
>> hw/qxl.c:    portio_list_add(qxl_vga_port_list,
>> pci_address_space_io(dev), 0x3b0);
>> hw/vga.c:        portio_list_add(vga_port_list, address_space_io, 0x3b0);
>
> That reminds me I should solve this in a more elegant way.
>
> qxl takes over the vga io ports.  The reason it does this is because qxl
> switches into vga mode in case the vga ports are accessed while not in
> vga mode.  After doing the check (and possibly switching mode) the vga
> handler is called to actually handle it.

The best way to handle this would be to remodel how we do VGA.

Make VGACommonState a proper QOM object and use it as the base class for
QXL, CirrusVGA, QEMUVGA (std-vga), and VMwareVGA.

The VGA accessors should be exposed as a memory region but the sub class
ought to be responsible for actually adding it to a subregion.

>
> That twist makes it a bit hard to convert vga ...
>
> Anyone knows how one would do that with the memory api instead? I think
> taking over the ports is easy as the memory regions have priorities so I
> can simply register a region with higher priority. I have no clue how to
> forward the access to the vga code though.
>

That should be possible with priorities, but I think it's wrong.  There
aren't two VGA devices.  QXL is-a VGA device and the best way to
override behavior of base VGA device is through polymorphism.

This isn't really a memory API issue, it's a modeling issue.

Regards,

Anthony Liguori

> Anyone has clues / suggestions?
>
> thanks,
>   Gerd