drm/i915/bdw: unleash PPGTT

v2: Squash in fix from Ben: Set PPGTT batches as necessary

This fixes the regression in the last couple of days when we enabled
PPGTT.

v3: Squash in fixup to still use GTT for secure batches from Ville:

BDW doesn't have a separate secure vs. non-secure bit in
MI_BATCH_BUFFER_START. So for secure batches we have to simply
leave the PPGTT bit unset. Fortunately older generations (except
HSW) had similar limitations so execbuffer already creates a GTT
mapping for all secure batches.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 78786c4..885d595 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1146,8 +1146,7 @@
 
 	/* snb/ivb/vlv conflate the "batch in ppgtt" bit with the "non-secure
 	 * batch" bit. Hence we need to pin secure batches into the global gtt.
-	 * hsw should have this fixed, but let's be paranoid and do it
-	 * unconditionally for now. */
+	 * hsw should have this fixed, but bdw mucks it up again. */
 	if (flags & I915_DISPATCH_SECURE && !batch_obj->has_global_gtt_mapping)
 		i915_gem_gtt_bind_object(batch_obj, batch_obj->cache_level);