Re: [Intel-gfx] [PATCH v6 08/17] drm/ttm: use gem vma_node

[Gerd Hoffmann]

 > Hi Gerd,
> 
> I've been seeing a regression on Nouveau with recent linux-next releases
> and git bisect points at this commit as the first bad one. If I revert
> it (there's a tiny conflict with a patch that was merged subsequently),
> things are back to normal.
> 
> I think the reason for this issue is that Nouveau doesn't use GEM
> objects for all buffer objects,

That shouldn't be a problem ...

> and even when it uses GEM objects, the
> code will not initialize the GEM object until after the buffer objects
> and the backing TTM objects have been created.

... but the initialization order is.

ttm_bo_uses_embedded_gem_object() assumes gem gets initialized first.

drm_gem_object_init() init calling drm_vma_node_reset() again is
probably the root cause for the breakage.

> I tried to fix that by making sure drm_gem_object_init() gets called by
> Nouveau before ttm_bo_init(), but the changes are fairly involved and I
> was unable to get the GEM reference counting right. I can look into the
> proper fix some more, but it might be worth reverting this patch for
> now to get Nouveau working again.

Changing the order doesn't look hard.  Patch attached (untested, have no
test hardware).  But maybe I missed some detail ...

The other patch attached works around the issue with a flag, to avoid
drm_vma_node_reset() being called twice.

cheers,
  Gerd