[igt-dev] [PATCH i-g-t 0/7] Prepare IGTs to allow only zero alignment

[Zbigniew Kempczyński]

On Thu, Oct 14, 2021 at 08:28:30AM -0700, Dixit, Ashutosh wrote:
> On Thu, 14 Oct 2021 01:19:10 -0700, Zbigniew Kempczyński wrote:
> >
> > In the future we're planning to allow passing only zero alignment so
> > this is preparation step to introduce check and disable or fix
> > igts which uses this constraint.
> >
> > v2: rename to gem_allows_obj_alignment() (Ashutosh)
> >     addressing review comments from Ashutosh
> >
> 
> For patches 1 through 6:
> 
> Reviewed-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
> 
> For patch 7, I think the point below from my earlier email is still
> unaddressed:
> 
> > So assigning a new offset will cause a new fault-in (bind) but not sure if
> > it will cause an actual fault-out (unbind). Though I am not sure if there
> > is actually a way to force it to happen if this doesn't work? Is there a
> > way to verify that the unbind is actually happening?
> 
> Maybe if assign the same offset to a different object/page that will cause
> a fault-out (unbind) followed by a fault-in (bind).

For softpin case if you're changing the offset i915 will unbind/bind vma
in ppgtt, see eb_vma_misplaced() condition:

	if (flags & EXEC_OBJECT_PINNED &&
	    vma->node.start != entry->offset)
		return true;

so when you will go out from eb_pin_vma() with an error in else {} part
i915_vma_unbind() will be called. You can verify this using dynamic ftrace.

I'm not able to do this on !ppgtt due to lack of such gen.

--
Zbigniew