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, 56 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index b1e3af7..95011df 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -914,6 +914,61 @@ static int intel_lid_present(void)
 #endif
 
 /**
+ * intel_find_lvds_downclock - find the reduced downclock for LVDS in EDID
+ * @dev: drm device
+ * @connector: LVDS connector
+ *
+ * Find the reduced downclock for LVDS in EDID.
+ */
+static void intel_find_lvds_downclock(struct drm_device *dev,
+				struct drm_connector *connector)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_display_mode *scan, *panel_fixed_mode;
+	int temp_downclock;
+
+	panel_fixed_mode = dev_priv->panel_fixed_mode;
+	temp_downclock = panel_fixed_mode->clock;
+
+	mutex_lock(&dev->mode_config.mutex);
+	list_for_each_entry(scan, &connector->probed_modes, head) {
+		/*
+		 * If one mode has the same resolution with the fixed_panel
+		 * mode while they have the different refresh rate, it means
+		 * that the reduced downclock is found for the LVDS. In such
+		 * case we can set the different FPx0/1 to dynamically select
+		 * between low and high frequency.
+		 */
+		if (scan->hdisplay == panel_fixed_mode->hdisplay &&
+			scan->hsync_start == panel_fixed_mode->hsync_start &&
+			scan->hsync_end == panel_fixed_mode->hsync_end &&
+			scan->htotal == panel_fixed_mode->htotal &&
+			scan->vdisplay == panel_fixed_mode->vdisplay &&
+			scan->vsync_start == panel_fixed_mode->vsync_start &&
+			scan->vsync_end == panel_fixed_mode->vsync_end &&
+			scan->vtotal == panel_fixed_mode->vtotal) {
+			if (scan->clock < temp_downclock) {
+				/*
+				 * The downclock is already found. But we
+				 * expect to find the lower downclock.
+				 */
+				temp_downclock = scan->clock;
+			}
+		}
+	}
+	mutex_unlock(&dev->mode_config.mutex);
+	if (temp_downclock < panel_fixed_mode->clock) {
+		/* We found the downclock for LVDS. */
+		dev_priv->lvds_downclock_avail = 1;
+		dev_priv->lvds_downclock = temp_downclock;
+		DRM_DEBUG_KMS("LVDS downclock is found in EDID. "
+				"Normal clock %dKhz, downclock %dKhz\n",
+				panel_fixed_mode->clock, temp_downclock);
+	}
+	return;
+}
+
+/**
  * intel_lvds_init - setup LVDS connectors on this device
  * @dev: drm device
  *
@@ -1023,6 +1078,7 @@ void intel_lvds_init(struct drm_device *dev)
 			dev_priv->panel_fixed_mode =
 				drm_mode_duplicate(dev, scan);
 			mutex_unlock(&dev->mode_config.mutex);
+			intel_find_lvds_downclock(dev, connector);
 			goto out;
 		}
 		mutex_unlock(&dev->mode_config.mutex);