drm/i915: Accept more fixed modes with VRR panels

It seem that when dealing with VRR capable eDP panels we need
to accept fixed modes with variable vblank length (which is what
VRR varies dynamically). Typically the preferred mode seems to be
a non-VRR more (lowish dotclock/refresh rate + short vblank).

We also have examples where it looks like even the hblank length
is a bit different between the preferred mode vs. VRR mode(s).
So let's just accept anything that has matching hdisp+vdisp+flags.

v2: Document that is_alt_drrs_mode() is a subset of is_alt_vrr_mode() (Jani)

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/125Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220531191844.11313-4-ville.syrjala@linux.intel.com

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

@@ -5216,7 +5216,8 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
 			      IS_ERR(edid) ? NULL : edid);
 
 	intel_panel_add_edid_fixed_modes(intel_connector,
-					 intel_connector->panel.vbt.drrs_type != DRRS_TYPE_NONE);
+					 intel_connector->panel.vbt.drrs_type != DRRS_TYPE_NONE,
+					 intel_vrr_is_capable(intel_connector));
 
 	/* MSO requires information from the EDID */
 	intel_edp_mso_init(intel_dp);

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

@@ -972,7 +972,8 @@ void intel_lvds_init(struct drm_i915_private *dev_priv)
 
 	/* Try EDID first */
 	intel_panel_add_edid_fixed_modes(intel_connector,
-					 intel_connector->panel.vbt.drrs_type != DRRS_TYPE_NONE);
+					 intel_connector->panel.vbt.drrs_type != DRRS_TYPE_NONE,
+					 false);
 
 	/* Failed to get EDID, what about VBT? */
 	if (!intel_panel_preferred_fixed_mode(intel_connector))

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

@@ -71,6 +71,27 @@ intel_panel_fixed_mode(struct intel_connector *connector,
 	return best_mode;
 }
 
+static bool is_alt_drrs_mode(const struct drm_display_mode *mode,
+			     const struct drm_display_mode *preferred_mode)
+{
+	return drm_mode_match(mode, preferred_mode,
+			      DRM_MODE_MATCH_TIMINGS |
+			      DRM_MODE_MATCH_FLAGS |
+			      DRM_MODE_MATCH_3D_FLAGS) &&
+		mode->clock != preferred_mode->clock;
+}
+
+static bool is_alt_vrr_mode(const struct drm_display_mode *mode,
+			    const struct drm_display_mode *preferred_mode)
+{
+	return drm_mode_match(mode, preferred_mode,
+			      DRM_MODE_MATCH_FLAGS |
+			      DRM_MODE_MATCH_3D_FLAGS) &&
+		mode->hdisplay == preferred_mode->hdisplay &&
+		mode->vdisplay == preferred_mode->vdisplay &&
+		mode->clock != preferred_mode->clock;
+}
+
 const struct drm_display_mode *
 intel_panel_downclock_mode(struct intel_connector *connector,
 			   const struct drm_display_mode *adjusted_mode)
@@ -83,7 +104,8 @@ intel_panel_downclock_mode(struct intel_connector *connector,
 	list_for_each_entry(fixed_mode, &connector->panel.fixed_modes, head) {
 		int vrefresh = drm_mode_vrefresh(fixed_mode);
 
-		if (vrefresh >= min_vrefresh && vrefresh < max_vrefresh) {
+		if (is_alt_drrs_mode(fixed_mode, adjusted_mode) &&
+		    vrefresh >= min_vrefresh && vrefresh < max_vrefresh) {
 			max_vrefresh = vrefresh;
 			best_mode = fixed_mode;
 		}
@@ -151,16 +173,18 @@ int intel_panel_compute_config(struct intel_connector *connector,
 }
 
 static bool is_alt_fixed_mode(const struct drm_display_mode *mode,
-			      const struct drm_display_mode *preferred_mode)
+			      const struct drm_display_mode *preferred_mode,
+			      bool has_vrr)
 {
-	return drm_mode_match(mode, preferred_mode,
-			      DRM_MODE_MATCH_TIMINGS |
-			      DRM_MODE_MATCH_FLAGS |
-			      DRM_MODE_MATCH_3D_FLAGS) &&
-		mode->clock != preferred_mode->clock;
+	/* is_alt_drrs_mode() is a subset of is_alt_vrr_mode() */
+	if (has_vrr)
+		return is_alt_vrr_mode(mode, preferred_mode);
+	else
+		return is_alt_drrs_mode(mode, preferred_mode);
 }
 
-static void intel_panel_add_edid_alt_fixed_modes(struct intel_connector *connector)
+static void intel_panel_add_edid_alt_fixed_modes(struct intel_connector *connector,
+						 bool has_vrr)
 {
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	const struct drm_display_mode *preferred_mode =
@@ -168,7 +192,7 @@ static void intel_panel_add_edid_alt_fixed_modes(struct intel_connector *connect
 	struct drm_display_mode *mode, *next;
 
 	list_for_each_entry_safe(mode, next, &connector->base.probed_modes, head) {
-		if (!is_alt_fixed_mode(mode, preferred_mode))
+		if (!is_alt_fixed_mode(mode, preferred_mode, has_vrr))
 			continue;
 
 		drm_dbg_kms(&dev_priv->drm,
@@ -226,11 +250,12 @@ static void intel_panel_destroy_probed_modes(struct intel_connector *connector)
 	}
 }
 
-void intel_panel_add_edid_fixed_modes(struct intel_connector *connector, bool has_drrs)
+void intel_panel_add_edid_fixed_modes(struct intel_connector *connector,
+				      bool has_drrs, bool has_vrr)
 {
 	intel_panel_add_edid_preferred_mode(connector);
-	if (intel_panel_preferred_fixed_mode(connector) && has_drrs)
-		intel_panel_add_edid_alt_fixed_modes(connector);
+	if (intel_panel_preferred_fixed_mode(connector) && (has_drrs || has_vrr))
+		intel_panel_add_edid_alt_fixed_modes(connector, has_vrr);
 	intel_panel_destroy_probed_modes(connector);
 }
 

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

@@ -40,7 +40,8 @@ int intel_panel_fitting(struct intel_crtc_state *crtc_state,
 			const struct drm_connector_state *conn_state);
 int intel_panel_compute_config(struct intel_connector *connector,
 			       struct drm_display_mode *adjusted_mode);
-void intel_panel_add_edid_fixed_modes(struct intel_connector *connector, bool has_drrs);
+void intel_panel_add_edid_fixed_modes(struct intel_connector *connector,
+				      bool has_drrs, bool has_vrr);
 void intel_panel_add_vbt_lfp_fixed_mode(struct intel_connector *connector);
 void intel_panel_add_vbt_sdvo_fixed_mode(struct intel_connector *connector);
 void intel_panel_add_encoder_fixed_mode(struct intel_connector *connector,

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

@@ -2910,7 +2910,7 @@ intel_sdvo_lvds_init(struct intel_sdvo *intel_sdvo, int device)
 
 	if (!intel_panel_preferred_fixed_mode(intel_connector)) {
 		intel_ddc_get_modes(connector, &intel_sdvo->ddc);
-		intel_panel_add_edid_fixed_modes(intel_connector, false);
+		intel_panel_add_edid_fixed_modes(intel_connector, false, false);
 	}
 
 	intel_panel_init(intel_connector);