drm/i915/skl: Add module parameter to select edp vswing table

This provides an option to override the value set by VBT
for selecting edp Vswing Pre-emph setting table.

v2: Adding comment about this being a temporary workaround and
making the parameter read-only (Jani)
v3: Changing mode to 0400 instead of 0 (Jani)

https://bugs.freedesktop.org/show_bug.cgi?id=89554
Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1364,7 +1364,6 @@ struct intel_vbt_data {
 	bool edp_initialized;
 	bool edp_support;
 	int edp_bpp;
-	bool edp_low_vswing;
 	struct edp_power_seq edp_pps;
 
 	struct {
@@ -1846,6 +1845,8 @@ struct drm_i915_private {
 		void (*stop_ring)(struct intel_engine_cs *ring);
 	} gt;
 
+	bool edp_low_vswing;
+
 	/*
 	 * NOTE: This is the dri1/ums dungeon, don't add stuff here. Your patch
 	 * will be rejected. Instead look for a better place.
@@ -2515,6 +2516,7 @@ struct i915_params {
 	int mmio_debug;
 	bool verbose_state_checks;
 	bool nuclear_pageflip;
+	int edp_vswing;
 };
 extern struct i915_params i915 __read_mostly;
 

drivers/gpu/drm/i915/i915_params.c

@@ -53,6 +53,7 @@ struct i915_params i915 __read_mostly = {
 	.mmio_debug = 0,
 	.verbose_state_checks = 1,
 	.nuclear_pageflip = 0,
+	.edp_vswing = 0,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -184,3 +185,10 @@ MODULE_PARM_DESC(verbose_state_checks,
 module_param_named_unsafe(nuclear_pageflip, i915.nuclear_pageflip, bool, 0600);
 MODULE_PARM_DESC(nuclear_pageflip,
 		 "Force atomic modeset functionality; only planes work for now (default: false).");
+
+/* WA to get away with the default setting in VBT for early platforms.Will be removed */
+module_param_named_unsafe(edp_vswing, i915.edp_vswing, int, 0400);
+MODULE_PARM_DESC(edp_vswing,
+		 "Ignore/Override vswing pre-emph table selection from VBT "
+		 "(0=use value from vbt [default], 1=low power swing(200mV),"
+		 "2=default swing(400mV))");

drivers/gpu/drm/i915/intel_bios.c

@@ -672,8 +672,13 @@ parse_edp(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
 	if (bdb->version >= 173) {
 		uint8_t vswing;
 
-		vswing = (edp->edp_vswing_preemph >> (panel_type * 4)) & 0xF;
-		dev_priv->vbt.edp_low_vswing = vswing == 0;
+		/* Don't read from VBT if module parameter has valid value*/
+		if (i915.edp_vswing) {
+			dev_priv->edp_low_vswing = i915.edp_vswing == 1;
+		} else {
+			vswing = (edp->edp_vswing_preemph >> (panel_type * 4)) & 0xF;
+			dev_priv->edp_low_vswing = vswing == 0;
+		}
 	}
 }
 

drivers/gpu/drm/i915/intel_ddi.c

@@ -282,7 +282,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port,
 		ddi_translations_fdi = NULL;
 		ddi_translations_dp = skl_ddi_translations_dp;
 		n_dp_entries = ARRAY_SIZE(skl_ddi_translations_dp);
-		if (dev_priv->vbt.edp_low_vswing) {
+		if (dev_priv->edp_low_vswing) {
 			ddi_translations_edp = skl_ddi_translations_edp;
 			n_edp_entries = ARRAY_SIZE(skl_ddi_translations_edp);
 		} else {

drivers/gpu/drm/i915/intel_dp.c

@@ -2894,7 +2894,7 @@ intel_dp_voltage_max(struct intel_dp *intel_dp)
 	if (IS_BROXTON(dev))
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 	else if (INTEL_INFO(dev)->gen >= 9) {
-		if (dev_priv->vbt.edp_low_vswing && port == PORT_A)
+		if (dev_priv->edp_low_vswing && port == PORT_A)
 			return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;
 	} else if (IS_VALLEYVIEW(dev))