drm/i915: Mark up the GTT flush following WC writes as ORIGIN_CPU

Similarly to invalidating beforehand, if the object is mmapped via
I915_MMAP_WC we cannot track writes through the I915_GEM_DOMAIN_GTT. At
the conclusion of the write, i915_gem_object_flush_gtt_writes() we also
need to treat the origin carefully in case it may have been untracked.

See also commit aeecc96 ("drm/i915: use ORIGIN_CPU for frontbuffer
invalidation on WC mmaps").

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818161718.27187-5-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -1450,7 +1450,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 	return ret;
 }
 
-static enum fb_op_origin
+static inline enum fb_op_origin
 write_origin(struct drm_i915_gem_object *obj, unsigned domain)
 {
 	return domain == I915_GEM_DOMAIN_GTT && !obj->has_wc_mmap ?
@@ -3155,7 +3155,7 @@ i915_gem_object_flush_gtt_write_domain(struct drm_i915_gem_object *obj)
 	old_write_domain = obj->base.write_domain;
 	obj->base.write_domain = 0;
 
-	intel_fb_obj_flush(obj, false, ORIGIN_GTT);
+	intel_fb_obj_flush(obj, false, write_origin(obj, I915_GEM_DOMAIN_GTT));
 
 	trace_i915_gem_object_change_domain(obj,
 					    obj->base.read_domains,