drm/i915: Stop duplicating the EDID fixed/downclock modes

Instead of duplicating the fixed/downclock modes we can just grab
the originals straight from the probed_modes list and keep them.
The next .get_modes() is going to repopulate the probed_modes list
anyway so whatever we leave there is just going to sit around until
that time wasting memory. In fact let's clear out the probed modes
list entirely to make sure we get 100% consistent behaviour starting
already from the very first real .get_modes().
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331112822.11462-7-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_panel.c

@@ -164,8 +164,7 @@ static void intel_panel_add_edid_downclock_mode(struct intel_connector *connecto
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	const struct drm_display_mode *fixed_mode =
 		intel_panel_preferred_fixed_mode(connector);
-	const struct drm_display_mode *scan, *best_mode = NULL;
-	struct drm_display_mode *downclock_mode;
+	struct drm_display_mode *scan, *best_mode = NULL;
 	int best_clock = fixed_mode->clock;
 
 	list_for_each_entry(scan, &connector->base.probed_modes, head) {
@@ -190,58 +189,54 @@ static void intel_panel_add_edid_downclock_mode(struct intel_connector *connecto
 	if (!best_mode)
 		return;
 
-	downclock_mode = drm_mode_duplicate(&dev_priv->drm, best_mode);
-	if (!downclock_mode)
-		return;
-
 	drm_dbg_kms(&dev_priv->drm,
-		    "[CONNECTOR:%d:%s] using downclock mode from EDID: " DRM_MODE_FMT "\n",
+		    "[CONNECTOR:%d:%s] using EDID downclock mode: " DRM_MODE_FMT "\n",
 		    connector->base.base.id, connector->base.name,
-		    DRM_MODE_ARG(downclock_mode));
+		    DRM_MODE_ARG(best_mode));
 
-	list_add_tail(&downclock_mode->head, &connector->panel.fixed_modes);
+	list_move_tail(&best_mode->head, &connector->panel.fixed_modes);
 }
 
 static void intel_panel_add_edid_fixed_mode(struct intel_connector *connector)
 {
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
-	const struct drm_display_mode *scan;
-	struct drm_display_mode *fixed_mode;
+	struct drm_display_mode *scan, *fixed_mode = NULL;
 
 	if (list_empty(&connector->base.probed_modes))
 		return;
 
-	/* prefer fixed mode from EDID if available */
+	/* make sure the preferred mode is first */
 	list_for_each_entry(scan, &connector->base.probed_modes, head) {
-		if ((scan->type & DRM_MODE_TYPE_PREFERRED) == 0)
-			continue;
-
-		fixed_mode = drm_mode_duplicate(&dev_priv->drm, scan);
-		if (!fixed_mode)
-			return;
-
-		drm_dbg_kms(&dev_priv->drm,
-			    "[CONNECTOR:%d:%s] using preferred mode from EDID: " DRM_MODE_FMT "\n",
-			    connector->base.base.id, connector->base.name,
-			    DRM_MODE_ARG(fixed_mode));
-
-		list_add_tail(&fixed_mode->head, &connector->panel.fixed_modes);
-		return;
+		if (scan->type & DRM_MODE_TYPE_PREFERRED) {
+			fixed_mode = scan;
+			break;
+		}
 	}
 
-	scan = list_first_entry(&connector->base.probed_modes,
-				typeof(*scan), head);
-	fixed_mode = drm_mode_duplicate(&dev_priv->drm, scan);
 	if (!fixed_mode)
-		return;
+		fixed_mode = list_first_entry(&connector->base.probed_modes,
+					      typeof(*fixed_mode), head);
 
-	fixed_mode->type |= DRM_MODE_TYPE_PREFERRED;
 	drm_dbg_kms(&dev_priv->drm,
-		    "[CONNECTOR:%d:%s] using first mode from EDID: " DRM_MODE_FMT "\n",
+		    "[CONNECTOR:%d:%s] using %s EDID fixed mode: " DRM_MODE_FMT "\n",
 		    connector->base.base.id, connector->base.name,
+		    fixed_mode->type & DRM_MODE_TYPE_PREFERRED ? "preferred" : "first",
 		    DRM_MODE_ARG(fixed_mode));
 
-	list_add_tail(&fixed_mode->head, &connector->panel.fixed_modes);
+	fixed_mode->type |= DRM_MODE_TYPE_PREFERRED;
+
+	list_move_tail(&fixed_mode->head, &connector->panel.fixed_modes);
+}
+
+static void intel_panel_destroy_probed_modes(struct intel_connector *connector)
+{
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct drm_display_mode *mode, *next;
+
+	list_for_each_entry_safe(mode, next, &connector->base.probed_modes, head) {
+		list_del(&mode->head);
+		drm_mode_destroy(&i915->drm, mode);
+	}
 }
 
 void intel_panel_add_edid_fixed_modes(struct intel_connector *connector, bool has_drrs)
@@ -249,6 +244,7 @@ void intel_panel_add_edid_fixed_modes(struct intel_connector *connector, bool ha
 	intel_panel_add_edid_fixed_mode(connector);
 	if (intel_panel_preferred_fixed_mode(connector) && has_drrs)
 		intel_panel_add_edid_downclock_mode(connector);
+	intel_panel_destroy_probed_modes(connector);
 }
 
 static void intel_panel_add_fixed_mode(struct intel_connector *connector,