some half-baked ttm ideas

Hi Christian,

I've been trying to move towards the idea of not having TTM manage the global TT, I'm still not sure what the result would look like so I've been randomly trying out a direction or two,

There are some patches in : https://github.com/airlied/linux/commits/ttm-half-baked-ideas

a) it splits use_tt into two flags, one for system memory backing and one for binding, and tries to use them correctly. b) adds cpu_pin/unpin hooks for the amdgpu/radeon drivers to use for userptr.

I sort of envision being able to set the use_tt flag to false for drivers who don't want TTM to maintain their global TT, but I'm still not certain how that would look, I'd welcome any input there.

Thanks, Dave.