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Re: [Xen-devel] RE: Help needed on gfx-passthrough

Dietmar Hahn wrote:
Am 18.03.2010 schrieb Han, Weidong:
There is a wiki page for xen gfx passthru: 
http://wiki.xensource.com/xenwiki/XenVGAPassthrough. pls read it.

Yes I did this.

I didn't try your gfx card. As you know, some vbios of nVidia gfx cards have 
vbios re-execution issue, which results in no display in VGA mode.

Yes I read this on the mailing list, you mean FLR issues?
Not exactly. Another possibility is that vbios bits may be truncated or modified after initialization in host, thus it might result in re-execution issue.

You can have a try with loading vbios from file and make vBAR = pBAR. You can 
find the corresponding patches in xen-devel mailing list.

I tried this already.
I want to look a little bit deeper to understand whats going on.
I saw your igd_passthru patch qemu hw/pci.c for special handling of some pci config registers of the host bridge and maybe I need a similar patch
for the special PCI Express Graphics Port bridge.
Discrete gfx card is an independent pci device. I don't think it will depend on platform. IGD is integrated in chipset, and there are some dependencies on chipset.
My problem is that I don't see any access to extended config registers.
PCIe extended config registers (>256bytes) are not virtualized in Xen qemu.

Therefore my question for help in debugging to see what the vgabios is doing.
I don't know how to see what vgabios is doing. If you can find the vgabios engineer, maybe you can dump and send gfx register values to him for analysis.


-----Original Message-----
From: Dietmar Hahn [mailto:dietmar.hahn@xxxxxxxxxxxxxx] Sent: Thursday, March 18, 2010 5:29 PM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Han, Weidong
Subject: Help needed on gfx-passthrough

Hi list,

I try to get gfx-passthrough on a laptop:
Intel PM45 Express chipset with extern nvidia craphics card G96M [Quadro FX 
I can't see the bios boot messages and also not the grub boot loader.
The domU linux boot messages appear on the screen.

For me it looks like the vgabios gets not started or works not well.
In the domU I can read the vgabios from /dev/mem and it's the same as in dom0.
If I change the hvmloader to use the standard vgabios from firmware/vgabios
I see the bios and grub boot messages.

I added some tracing to qemu-dm (pt_*read/write and pci_*read/write) to see
accesses to the emulated chipset and graphics card but I can see no difference
between using the original vgabios or the emulated vgabios within the hvmloader.

Now my question: how can I debug this problem. How can I see whether the vgabios
gets started and initialises the graphics card? I'am not fit enough in this area and documentation is very rare!
Thanks in advance!


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