Re: [Xen-devel] xen and agpgart

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> That was actually my initial attempt.  The first problem I ran into was it
> attempting to do a cache flush:
> 
> #define flush_agp_cache() asm volatile("wbinvd":::"memory")

We can fix this by virtualising the instruction. But we can ignore it
for now.

> Which causes a general protection fault.  Ignoring that for the moment and
> then working forward, it allocates a page of memory with __get_free_page()
> and attempts to ioremap_nocache() it to presumably generate a completely
> uncached page in memory.  This results in a strange oops attempting to
> fiddle with the page tables changing the page attributes on that piece
> of memory.

Hmmmm.... I think the problem is people using virt_to_phys() instead
of virt_to_bus(). I would have expected the latter to be correct
really. I'll take a look at uses of ioremap() and ioremap_nocache()
throughout Linux. It may be there's a simple fix that will work for all
uses... You could try manually changing the address passed in to
virt_to_bus() and see if you get fiurther.

 -- Keir

> My goal at the moment is to have the machine's head running in dom0 (and
> on the i830-ish machine I have as a target, this is going to require the
> agpgart working to have any reasonable X on it).
> 
>                               -- Gerald
> 
> On Sat, Sep 04, 2004 at 02:11:20AM +0100, Keir Fraser wrote:
> > The answer may well be "nothing" if you just want GART/DRI in
> > DOM0. Probably those source driectories haven't been enabled in the
> > Xen arachitecture for 2.6 - if you can do that then try compiling teh
> > drivers and see what happens!
> > 
> >  -- Keir
> > 
> > > I've just started toying with xen and noticed the lack of support for
> > > agpgart.  It looks like the reasons for this lack have changed between 1.2
> > > and 2.0 and It looks like it's a lot closer to working now.  I 
> > > unfortunately
> > > do not have much experience doing VM programming, so my understanding of
> > > what's needed may be a little lacking.  I was wondering if someone with a
> > > little more knowledge of VM's and Xen than I could comment before I start
> > > digging further into it on what work needs to be done in Xen to make
> > > agpgart/drm/etc. work in Xen.  Thanks in advance.
> > > 
> > >                           -- Gerald
> > > 
> > > 
> > > 
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