drm/i915: Use ORIGIN_CPU for fb invalidation from pwrite

As pwrite does not use the fence for its GTT access, and may even go
through a secondary interface avoiding the main VMA, we cannot treat the
write as automatically invalidated by the hardware and so we require
ORIGIN_CPU frontbufer invalidate/flushes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818161718.27187-4-chris@chris-wilson.co.uk
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -1082,7 +1082,7 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_private *i915,
 	if (ret)
 		goto out_unpin;
 
-	intel_fb_obj_invalidate(obj, ORIGIN_GTT);
+	intel_fb_obj_invalidate(obj, ORIGIN_CPU);
 	obj->dirty = true;
 
 	user_data = u64_to_user_ptr(args->data_ptr);
@@ -1149,7 +1149,7 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_private *i915,
 		}
 	}
 
-	intel_fb_obj_flush(obj, false, ORIGIN_GTT);
+	intel_fb_obj_flush(obj, false, ORIGIN_CPU);
 out_unpin:
 	if (node.allocated) {
 		wmb();