drm/i915: Set the Z inversion overlap field

Dual link Z-inversion overlap field is present
in MIPI_CTRL register unlike the older platforms,
hence setting the same in this patch.
Signed-off-by: Deepak M <m.deepak@intel.com>
Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487078180-15147-5-git-send-email-madhav.chauhan@intel.com

drivers/gpu/drm/i915/intel_dsi.c

@@ -456,13 +456,22 @@ static void intel_dsi_port_enable(struct intel_encoder *encoder)
 
 	if (intel_dsi->dual_link == DSI_DUAL_LINK_FRONT_BACK) {
 		u32 temp;
-
+		if (IS_GEN9_LP(dev_priv)) {
+			for_each_dsi_port(port, intel_dsi->ports) {
+				temp = I915_READ(MIPI_CTRL(port));
+				temp &= ~BXT_PIXEL_OVERLAP_CNT_MASK |
+					intel_dsi->pixel_overlap <<
+					BXT_PIXEL_OVERLAP_CNT_SHIFT;
+				I915_WRITE(MIPI_CTRL(port), temp);
+			}
+		} else {
 			temp = I915_READ(VLV_CHICKEN_3);
 			temp &= ~PIXEL_OVERLAP_CNT_MASK |
 					intel_dsi->pixel_overlap <<
 					PIXEL_OVERLAP_CNT_SHIFT;
 			I915_WRITE(VLV_CHICKEN_3, temp);
 		}
+	}
 
 	for_each_dsi_port(port, intel_dsi->ports) {
 		i915_reg_t port_ctrl = IS_GEN9_LP(dev_priv) ?