drm/i915: clarify gen2 pageflip cmd

I've reviewed gen2 pageflip code to hunt down multiple prepare pageflip
issues. The only thing I've found is a slight but functionally
meaningless confusion about the length of the mi cmd.

Fix it up and add a comment about what this dword should be (according
to docs at least).

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ebe71ed..4247a7b 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7288,7 +7288,7 @@ static int intel_gen2_queue_flip(struct drm_device *dev,
                 MI_DISPLAY_FLIP_PLANE(intel_crtc->plane));
        OUT_RING(fb->pitches[0]);
        OUT_RING(obj->gtt_offset + offset);
-       OUT_RING(MI_NOOP);
+       OUT_RING(0); /* aux display base address, unused */
        ADVANCE_LP_RING();
 out:
        return ret;