drm/i915: Check whether the LVDS downclock is found in VBT

Enumerate the LVDS panel timing info entry list in VBT to check whether
the LVDS downclock is found. If found, the downclock is also used to switch
dynamically between low and high frequency for LVDS.
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_bios.c

@@ -114,6 +114,8 @@ parse_lfp_panel_data(struct drm_i915_private *dev_priv,
 	struct lvds_dvo_timing *dvo_timing;
 	struct drm_display_mode *panel_fixed_mode;
 	int lfp_data_size, dvo_timing_offset;
+	int i, temp_downclock;
+	struct drm_display_mode *temp_mode;
 
 	/* Defaults if we can't find VBT info */
 	dev_priv->lvds_dither = 0;
@@ -162,6 +164,46 @@ parse_lfp_panel_data(struct drm_i915_private *dev_priv,
 	DRM_DEBUG_KMS("Found panel mode in BIOS VBT tables:\n");
 	drm_mode_debug_printmodeline(panel_fixed_mode);
 
+	temp_mode = kzalloc(sizeof(*temp_mode), GFP_KERNEL);
+	temp_downclock = panel_fixed_mode->clock;
+	/*
+	 * enumerate the LVDS panel timing info entry in VBT to check whether
+	 * the LVDS downclock is found.
+	 */
+	for (i = 0; i < 16; i++) {
+		entry = (struct bdb_lvds_lfp_data_entry *)
+			((uint8_t *)lvds_lfp_data->data + (lfp_data_size * i));
+		dvo_timing = (struct lvds_dvo_timing *)
+			((unsigned char *)entry + dvo_timing_offset);
+
+		fill_detail_timing_data(temp_mode, dvo_timing);
+
+		if (temp_mode->hdisplay == panel_fixed_mode->hdisplay &&
+		temp_mode->hsync_start == panel_fixed_mode->hsync_start &&
+		temp_mode->hsync_end == panel_fixed_mode->hsync_end &&
+		temp_mode->htotal == panel_fixed_mode->htotal &&
+		temp_mode->vdisplay == panel_fixed_mode->vdisplay &&
+		temp_mode->vsync_start == panel_fixed_mode->vsync_start &&
+		temp_mode->vsync_end == panel_fixed_mode->vsync_end &&
+		temp_mode->vtotal == panel_fixed_mode->vtotal &&
+		temp_mode->clock < temp_downclock) {
+			/*
+			 * downclock is already found. But we expect
+			 * to find the lower downclock.
+			 */
+			temp_downclock = temp_mode->clock;
+		}
+		/* clear it to zero */
+		memset(temp_mode, 0, sizeof(*temp_mode));
+	}
+	kfree(temp_mode);
+	if (temp_downclock < panel_fixed_mode->clock) {
+		dev_priv->lvds_downclock_avail = 1;
+		dev_priv->lvds_downclock = temp_downclock;
+		DRM_DEBUG_KMS("LVDS downclock is found in VBT. ",
+				"Normal Clock %dKHz, downclock %dKHz\n",
+				temp_downclock, panel_fixed_mode->clock);
+	}
 	return;
 }