Radeon HD5770 and VGA passthrough (vBAR=pBAR not enough?)

[FeepingCreature <default_357-line@yahoo.de>]

Hi,

I've been trying these last few days to get primary VGA passthrough to
work on my ATI Radeon HD5770 card.

I'm running hg head with the secondary patches applied (external
graphics BIOS, vbar=pbar), and in VGA mode this works fine.

The problem is that ati2dvag crashes whenever it tries to switch to any
driver-run graphics mode.

------ win xp starts its vga-based boot screen. All is well.
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=c0000 mfn=c0000 nr_mfns=10000
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=d0020 mfn=d0020 nr_mfns=20
(XEN) domctl.c:1072:d0 ioport_map:remove f_gport=d000 f_mport=d000 np=100
(XEN) domctl.c:992:d0 memory_map:add: gfn=c0000 mfn=c0000 nr_mfns=10000
(XEN) domctl.c:992:d0 memory_map:add: gfn=d0020 mfn=d0020 nr_mfns=20
(XEN) domctl.c:1048:d0 ioport_map:add f_gport=d000 f_mport=d000 np=100
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=f1000 mfn=d0040 nr_mfns=4
(XEN) domctl.c:992:d0 memory_map:add: gfn=f1000 mfn=d0040 nr_mfns=4
(XEN) grant_table.c:1121:d8 Expanding dom (8) grant table from (4) to
(32) frames.
(XEN) irq.c:309: Dom8 callback via changed to GSI 28
------ driver activation happens here
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=c0000 mfn=c0000 nr_mfns=10000
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=d0020 mfn=d0020 nr_mfns=20
(XEN) domctl.c:1072:d0 ioport_map:remove f_gport=d000 f_mport=d000 np=100
-- note the different addresses!
(XEN) domctl.c:992:d0 memory_map:add: gfn=e0000 mfn=c0000 nr_mfns=10000
(XEN) domctl.c:992:d0 memory_map:add: gfn=fbfe0 mfn=d0020 nr_mfns=20
(XEN) domctl.c:1048:d0 ioport_map:add f_gport=d000 f_mport=d000 np=100
(XEN) domctl.c:1002:d0 memory_map:remove: gfn=f1000 mfn=d0040 nr_mfns=4
(XEN) domctl.c:992:d0 memory_map:add: gfn=f1000 mfn=d0040 nr_mfns=4

So the graphics card driver evidently tries to allocate its resources
somewhere else than where they start out as. If I boot into VGA mode,
the resources tab of the card confirms this.

I have a sneaking suspicion that this breaks vBAR=pBAR, but I don't know
how to verify or fix it. I believe that the correct thing to do might be
to reallocate the graphics card's resources at the new address windows
gives me, but I have no idea how to go about that. Any help would be
appreciated.