RE: [Xen-devel] agp and framebuffer (intelfb) - your milage may vary

["B.G. Bruce" <bgb@xxxxxxxxx>]

On Fri, 2005-01-28 at 04:43, Ian Pratt wrote:
> > with the patches/linux-2.6.9/{agpgart,drm}.patch patches applied
> > (shouldn't there be a symlink to linux-2.6.10?) 
> 
> There's an argument that we should automatically apply these patches and
> build AGP and DRM support as modules for our xen0 kernels. It would be
> good to know which drivers have actually been tested and work.
> 
> Rik: did you have any luck feeding the agpgart and drm patches up
> stream? 
> 
> > I would
> > appreciate it if someone who knows the xen agp subsystem (in 
> > particular
> > the agp_acquire_backend) better would look over the intelfb.patch and
> > post any improvements (I don't like taking out the checks made on
> > agp_acquire_backend(), but with them left in, I get "intelfb: cannot
> > acquire agp").
> 
> Which of the error codes is it returning? There's nothing special about
> AGP support on arch xen, its just that Xen is rather stricter about what
> drivers are allowed to get away with, requring some fixes.
> 
> int agp_backend_acquire(void)
> {
>         if (agp_bridge->type == NOT_SUPPORTED)
>                 return -EINVAL;
>         if (atomic_read(&agp_bridge->agp_in_use))
>                 return -EBUSY;
>         atomic_inc(&agp_bridge->agp_in_use);
>         return 0;
> }
> 
> Ian

Yes, it it - which is why I'm confused why the intelfb (unpateched)
works fine on a non xen environment, but fails under xen.  Obviously,
what is being returned from agp_backend_acquire() is different, however
if the test on the return is removed, the driver loads and functions
normally.  With the tests in place, the driver still loads, but reports
"cannot acquire agp" and you cannot "use" the intelfb even though a
lsmod shows it hooked in.

+/*     if (agp_backend_acquire()) {
+*              ERR_MSG("cannot acquire agp\n");
+*              cleanup(dinfo);
+*              return -ENODEV;
+*      } */

Obviously, what agp_backen_acquire is returning has changed, but it can
only be one of (-EINVAL,-EBUSY,0).  Which one will xen be feeding it?

B.

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