[Beignet] Haswell issues

[Rebecca N. Palmer]

> After revert the beignet's atomic in l3 patch [9e8874c ?], the i915.enable_ppgtt=2 should work for HSW platform.
If it's that easy to really fix this, I agree we should do so; I'd taken 
the absence of anything other than "patch the kernel" in the 
documentation to mean that no other fix was known.

> Daniel already submitted a patchset to address part of this issue.
http://lists.freedesktop.org/archives/intel-gfx/2015-April/064635.html ?

> could you help to identify the first kernel version which this enable_ppgtt=2 works for beignet?
Looks like 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=78a423772d08eb5a048765a883b5b5a308ea0d0f 
but I don't have the hardware to try it.