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>

1 files changed, 14 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 33113c7d4e49..a65838ed24b9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2869,14 +2869,25 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
                 return -EINVAL;
         }
 
-        if (limit->find_reduced_pll && dev_priv->lvds_downclock_avail) {
+        if (is_lvds && limit->find_reduced_pll &&
+                        dev_priv->lvds_downclock_avail) {
                 memcpy(&reduced_clock, &clock, sizeof(intel_clock_t));
                 has_reduced_clock = limit->find_reduced_pll(limit, crtc,
-                                                            (adjusted_mode->clock*3/4),
+                                                            dev_priv->lvds_downclock,
                                                             refclk,
                                                             &reduced_clock);
+                if (has_reduced_clock && (clock.p != reduced_clock.p)) {
+                        /*
+                         * If the different P is found, it means that we can't
+                         * switch the display clock by using the FP0/FP1.
+                         * In such case we will disable the LVDS downclock
+                         * feature.
+                         */
+                        DRM_DEBUG_KMS("Different P is found for "
+                                                "LVDS clock/downclock\n");
+                        has_reduced_clock = 0;
+                }
         }
-
         /* SDVO TV has fixed PLL values depend on its clock range,
            this mirrors vbios setting. */
         if (is_sdvo && is_tv) {