drm/i915: Introduce intel_ddi_dp_voltage_max()

Rather than sprinkling ideas of how big the DDI buf translation tables
are somewhere in intel_dp.c, let's concentrate it all in intel_ddi.c
where the actual tables are defined. To that end we introduce
intel_ddi_dp_voltage_max() which will actually look at the proper
translation table to determine what is the maximum voltage swing level
supported.

v2: Mask out the preemphasis bits from the return value of
    intel_ddi_dp_voltage_max()
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170223174901.26749-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_ddi.c

@@ -1615,6 +1615,25 @@ static void bxt_ddi_vswing_sequence(struct drm_i915_private *dev_priv,
 				     ddi_translations[level].deemphasis);
 }
 
+u8 intel_ddi_dp_voltage_max(struct intel_encoder *encoder)
+{
+	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
+	int n_entries;
+
+	if (encoder->type == INTEL_OUTPUT_EDP)
+		intel_ddi_get_buf_trans_edp(dev_priv, &n_entries);
+	else
+		intel_ddi_get_buf_trans_dp(dev_priv, &n_entries);
+
+	if (WARN_ON(n_entries < 1))
+		n_entries = 1;
+	if (WARN_ON(n_entries > ARRAY_SIZE(index_to_dp_signal_levels)))
+		n_entries = ARRAY_SIZE(index_to_dp_signal_levels);
+
+	return index_to_dp_signal_levels[n_entries - 1] &
+		DP_TRAIN_VOLTAGE_SWING_MASK;
+}
+
 static uint32_t translate_signal_level(int signal_levels)
 {
 	int i;

drivers/gpu/drm/i915/intel_dp.c

@@ -3098,9 +3098,8 @@ intel_dp_voltage_max(struct intel_dp *intel_dp)
 	if (IS_GEN9_LP(dev_priv))
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 	else if (INTEL_GEN(dev_priv) >= 9) {
-		if (dev_priv->vbt.edp.low_vswing && port == PORT_A)
-			return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
-		return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;
+		struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+		return intel_ddi_dp_voltage_max(encoder);
 	} else if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 	else if (IS_GEN7(dev_priv) && port == PORT_A)

drivers/gpu/drm/i915/intel_drv.h

@@ -1233,6 +1233,8 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
 			 struct intel_crtc_state *pipe_config);
 void intel_ddi_set_vc_payload_alloc(struct drm_crtc *crtc, bool state);
 uint32_t ddi_signal_levels(struct intel_dp *intel_dp);
+u8 intel_ddi_dp_voltage_max(struct intel_encoder *encoder);
+
 unsigned int intel_fb_align_height(struct drm_i915_private *dev_priv,
 				   unsigned int height,
 				   uint32_t pixel_format,