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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 30/01/2013 17:33, Anthony Liguori ha scritto:
> 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.

I think QXL should have-a VGA rather than being one.  It completely
bypasses the VGA infrastructure if not in VGA mode.

> 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.

Avi had a prototype patch series for IOMMU regions.  You could add one
between the QXL device and the VGA.  It doesn't have to do a
translation, but trying to translate a VGA address already means that
you must go to VGA mode.

Paolo

> 
> 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
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