drm/i915/bios: use a flag for vbt hdmi level shift presence

The pre-initialized magic value is a bit silly, switch to a flag
instead.

v2: Reduce paranoia to a single sanity check (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/74fe24ab6d5f0ea2ff2059cdf044d6d3006080fc.1573227240.git.jani.nikula@intel.com

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

@@ -1509,6 +1509,7 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv,
 			      port_name(port),
 			      hdmi_level_shift);
 		info->hdmi_level_shift = hdmi_level_shift;
+		info->hdmi_level_shift_set = true;
 	}
 
 	if (bdb_version >= 204) {
@@ -1692,8 +1693,6 @@ parse_general_definitions(struct drm_i915_private *dev_priv,
 static void
 init_vbt_defaults(struct drm_i915_private *dev_priv)
 {
-	enum port port;
-
 	dev_priv->vbt.crt_ddc_pin = GMBUS_PIN_VGADDC;
 
 	/* Default to having backlight */
@@ -1721,13 +1720,6 @@ init_vbt_defaults(struct drm_i915_private *dev_priv)
 	dev_priv->vbt.lvds_ssc_freq = intel_bios_ssc_frequency(dev_priv,
 			!HAS_PCH_SPLIT(dev_priv));
 	DRM_DEBUG_KMS("Set default to SSC at %d kHz\n", dev_priv->vbt.lvds_ssc_freq);
-
-	for_each_port(port) {
-		struct ddi_vbt_port_info *info =
-			&dev_priv->vbt.ddi_port_info[port];
-
-		info->hdmi_level_shift = HDMI_LEVEL_SHIFT_UNKNOWN;
-	}
 }
 
 /* Defaults to initialize only if there is no VBT. */

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

@@ -888,11 +888,10 @@ icl_get_combo_buf_trans(struct drm_i915_private *dev_priv, int type, int rate,
 
 static int intel_ddi_hdmi_level(struct drm_i915_private *dev_priv, enum port port)
 {
+	struct ddi_vbt_port_info *port_info = &dev_priv->vbt.ddi_port_info[port];
 	int n_entries, level, default_entry;
 	enum phy phy = intel_port_to_phy(dev_priv, port);
 
-	level = dev_priv->vbt.ddi_port_info[port].hdmi_level_shift;
-
 	if (INTEL_GEN(dev_priv) >= 12) {
 		if (intel_phy_is_combo(dev_priv, phy))
 			icl_get_combo_buf_trans(dev_priv, INTEL_OUTPUT_HDMI,
@@ -927,12 +926,14 @@ static int intel_ddi_hdmi_level(struct drm_i915_private *dev_priv, enum port por
 		return 0;
 	}
 
-	/* Choose a good default if VBT is badly populated */
-	if (level == HDMI_LEVEL_SHIFT_UNKNOWN || level >= n_entries)
-		level = default_entry;
-
 	if (WARN_ON_ONCE(n_entries == 0))
 		return 0;
+
+	if (port_info->hdmi_level_shift_set)
+		level = port_info->hdmi_level_shift;
+	else
+		level = default_entry;
+
 	if (WARN_ON_ONCE(level >= n_entries))
 		level = n_entries - 1;
 

drivers/gpu/drm/i915/i915_drv.h

@@ -627,13 +627,9 @@ struct ddi_vbt_port_info {
 
 	int max_tmds_clock;
 
-	/*
-	 * This is an index in the HDMI/DVI DDI buffer translation table.
-	 * The special value HDMI_LEVEL_SHIFT_UNKNOWN means the VBT didn't
-	 * populate this field.
-	 */
-#define HDMI_LEVEL_SHIFT_UNKNOWN	0xff
+	/* This is an index in the HDMI/DVI DDI buffer translation table. */
 	u8 hdmi_level_shift;
+	u8 hdmi_level_shift_set:1;
 
 	u8 supports_dvi:1;
 	u8 supports_hdmi:1;