drm/i915: Assume dual channel LVDS if pixel clock necessitates it

l1k · jnikula · commit 6f317cfe42c9 · 2015-05-05T17:09:44.000+03:00
Single channel LVDS maxes out at 112 MHz, anything above must be dual channel. This avoids the need to specify i915.lvds_channel_mode=2 on all 17" MacBook Pro models with i915 graphics since they had 1920x1200 (193 MHz), plus those 15" pre-retina models which had a resolution of 1680x1050 (119 MHz) as a BTO option. Source for 112 MHz limit of single channel LVDS is section 2.3 of: https://01.org/linuxgraphics/sites/default/files/documentation/ivb_ihd_os_vol3_part4.pdf v2: Avoid hardcoding 17" models by assuming dual channel LVDS if the resolution necessitates it, suggested by Jani Nikula. v3: Fix typo, thanks Joonas Lahtinen. v4: Split commit in two, suggested by Ville Syrjälä. Signed-off-by: Lukas Wunner <lukas@wunner.de> Tested-by: Lukas Wunner <lukas@wunner.de> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: stable@vger.kernel.org [Jani: included spec reference into the commit message] Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
@@ -848,6 +848,11 @@ static bool compute_is_dual_link_lvds(struct intel_lvds_encoder *lvds_encoder)
 	if (i915.lvds_channel_mode > 0)
 		return i915.lvds_channel_mode == 2;
 
+	/* single channel LVDS is limited to 112 MHz */
+	if (lvds_encoder->attached_connector->base.panel.fixed_mode->clock
+	    > 112999)
+		return true;
+
 	if (dmi_check_system(intel_dual_link_lvds))
 		return true;
 
@@ -1111,6 +1116,8 @@ void intel_lvds_init(struct drm_device *dev)
 out:
 	mutex_unlock(&dev->mode_config.mutex);
 
+	intel_panel_init(&intel_connector->panel, fixed_mode, downclock_mode);
+
 	lvds_encoder->is_dual_link = compute_is_dual_link_lvds(lvds_encoder);
 	DRM_DEBUG_KMS("detected %s-link lvds configuration\n",
 		      lvds_encoder->is_dual_link ? "dual" : "single");
@@ -1125,7 +1132,6 @@ void intel_lvds_init(struct drm_device *dev)
 	}
 	drm_connector_register(connector);
 
-	intel_panel_init(&intel_connector->panel, fixed_mode, downclock_mode);
 	intel_panel_setup_backlight(connector, INVALID_PIPE);
 
 	return;
