From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [Qemu-devel] KVM call minutes 2013-01-29 - Port I/O
Date: Wed, 30 Jan 2013 10:33:35 -0600
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References: <871ud4gfoa.fsf@elfo.elfo> <5109065B.4060803@suse.de> <51094024.20803@redhat.com>
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Cc: Juan Quintela <quintela@redhat.com>,
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	qemu-devel <qemu-devel@nongnu.org>,
	Alexander Graf <agraf@suse.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	qemu-ppc <qemu-ppc@nongnu.org>,
	=?utf-8?Q?Herv=C3=A9?= Poussineau <hpoussin@reactos.org>,
	David Gibson <david@gibson.dropbear.id.au>,
	Alon Levy <alevy@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>
To: Gerd Hoffmann <kraxel@redhat.com>,
	Andreas =?utf-8?Q?F=C3=A4rber?= <afaerber@suse.de>
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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