Re: [Xen-devel] [Xen-users] VGA passthough still not working

[Doug Magee <djmagee@xxxxxxxxxxxx>]

On Wed, 2012-01-25 at 20:52 +0100, Pavel MatÄja wrote:
> On Wed 25. of January 2012 20:29:12 Pavel MatÄja wrote:
> > On Wed 25. of January 2012 17:52:11 Doug Magee wrote:
> > > Also, i believe you said the card you're trying to pass through is not
> > > the primary card in your host system.  If that's the case, don't use
> > > gfx_passthru or expect to get the video bios working.  The 'primary'
> > > video adapter owns certain io ports and memory areas that are consitent
> > > from machine to machine.  Also, the system will copy the vbios from the
> > > card to a location in memory (0xc0000) so it can execute at boot time.
> > > 
> > > Xen's gfx_passthru code depends on all of these factors.  As the code
> > > stands, if you use gfx_passthru on a secondary card, it will still copy
> > > the vbios from the primary card (as it simply reads memory from
> > > 0xc0000), and directly map io ports and low memory areas to those used
> > > by the primary card in the host system.  In this case the guest will
> > > almost certainly never get past executing ROMBIOS, and the host may or
> > > may not lock up or experience 'issues'.
> > 
> > This will do the trick with secondary card (replace path to VGA BIOS):
> > 
> > --- xen-unstable.hg.working/tools/ioemu-remote/hw/pt-graphics.c 2012-01-25
> > 20:26:37.927654890 +0100
> > +++ xen-unstable.hg.working.generic/tools/ioemu-remote/hw/pt-graphics.c
> > 2011-07-30 13:57:57.347396095 +0200
> > @@ -487,10 +487,10 @@
> >  {
> >      int fd;
> >      uint32_t bios_size = 0;
> > -    uint32_t start = 0;
> > +    uint32_t start = 0xC0000;
> >      uint16_t magic = 0;
> > 
> > -    if ( (fd = open("/lib/firmware/ASUS.HD6850.1024.101007.bin",
> > O_RDONLY)) < 0 )
> > +    if ( (fd = open("/dev/mem", O_RDONLY)) < 0 )
> >      {
> >          PT_LOG("Error: Can't open /dev/mem: %s\n", strerror(errno));
> >          return 0;
> 
> Sorry, switch the + and -.

This will load the proper BIOS, but it seems this wouldn't be enough.
In hw/pt-graphics.c:register_vga_regions(), we map 1:1 ioports
0x3b0-0x3bb, 0x3c0-0x3df, and memory at 0xa0000-0xbffff.

If i understand this correctly, these ioports and memory areas are bound
to the primary video adapter in the host on boot by the BIOS, depending
on what device you've selected in the BIOS setup screen to be your
primary adapter.  Therefore, you could load the proper bios, but it
would still write to memory and io ports that are bound to the primary
card in the host, not the card being passed through to the guest.

Does this make sense? (Or, am i nuts?)



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel