drm/i915: Enable LVDS downclock feature through EDID.

If more than one mode with the same resolution defined in EDID has different
refresh rate, it is thought that the downclock is found for LVDS.
We will program the different FPx0/1 register so that we can select dynamically
between the low and high frequency.

On the g4x platform we will use the CxSR feature to switch the different
refresh rate if the LVDS downclock feature is supported.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 835625b..dcc061c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -539,6 +539,8 @@
 	/* Reclocking support */
 	bool render_reclock_avail;
 	bool lvds_downclock_avail;
+	/* indicates the reduced downclock for LVDS*/
+	int lvds_downclock;
 	struct work_struct idle_work;
 	struct timer_list idle_timer;
 	bool busy;