https://bugs.freedesktop.org/show_bug.cgi?id=90537
--- Comment #24 from Michel Dänzer michel@daenzer.net --- (In reply to Christian König from comment #23)
How would it break backwards compatibility?
You would need to allow multiple mappings into the same address space per BO.
Which is exactly what I've did for amdgpu, but IIRC that would break the userspace interface because you won't return the mapped address any more when you try to map it multiple times....
What would that break? It could result in the same BO having several representations in userspace, but (why) is that a problem?
I'm not sure how not tracking the VA ranges per GEM handle could ever work as expected with several GEM handles referencing the same BO.
Actually it can indeed never work correctly. What we just do all the time is trying to avoid the case that several GEM handles reference the same BO very hard.
I'm afraid we can't always avoid that though, e.g. when sharing BOs between glamor and the Xorg driver.