drm/i915: fix calculation of eDP signal levels on Sandybridge

Some voltage swing/pre-emphasis level use the same value on eDP
Sandybridge, like 400mv_0db and 600mv_0db are with the same value
of (0x0 << 22). So, fix them, and point out the value if it isn't
a supported voltage swing/pre-emphasis level.
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

drivers/gpu/drm/i915/i915_reg.h

@@ -3174,10 +3174,11 @@
 #define  EDP_LINK_TRAIN_600MV_3_5DB_SNB_A	(0x01<<22)
 #define  EDP_LINK_TRAIN_800MV_0DB_SNB_A		(0x0<<22)
 /* SNB B-stepping */
-#define  EDP_LINK_TRAIN_400MV_0DB_SNB_B		(0x0<<22)
-#define  EDP_LINK_TRAIN_400MV_6DB_SNB_B		(0x3a<<22)
-#define  EDP_LINK_TRAIN_600MV_3_5DB_SNB_B	(0x39<<22)
-#define  EDP_LINK_TRAIN_800MV_0DB_SNB_B		(0x38<<22)
+#define  EDP_LINK_TRAIN_400_600MV_0DB_SNB_B	(0x0<<22)
+#define  EDP_LINK_TRAIN_400MV_3_5DB_SNB_B	(0x1<<22)
+#define  EDP_LINK_TRAIN_400_600MV_6DB_SNB_B	(0x3a<<22)
+#define  EDP_LINK_TRAIN_600_800MV_3_5DB_SNB_B	(0x39<<22)
+#define  EDP_LINK_TRAIN_800_1200MV_0DB_SNB_B	(0x38<<22)
 #define  EDP_LINK_TRAIN_VOL_EMP_MASK_SNB	(0x3f<<22)
 
 #define  FORCEWAKE				0xA18C

drivers/gpu/drm/i915/intel_dp.c

@@ -1153,18 +1153,27 @@ intel_dp_signal_levels(uint8_t train_set, int lane_count)
 static uint32_t
 intel_gen6_edp_signal_levels(uint8_t train_set)
 {
-	switch (train_set & (DP_TRAIN_VOLTAGE_SWING_MASK|DP_TRAIN_PRE_EMPHASIS_MASK)) {
+	int signal_levels = train_set & (DP_TRAIN_VOLTAGE_SWING_MASK |
+					 DP_TRAIN_PRE_EMPHASIS_MASK);
+	switch (signal_levels) {
 	case DP_TRAIN_VOLTAGE_SWING_400 | DP_TRAIN_PRE_EMPHASIS_0:
-		return EDP_LINK_TRAIN_400MV_0DB_SNB_B;
+	case DP_TRAIN_VOLTAGE_SWING_600 | DP_TRAIN_PRE_EMPHASIS_0:
+		return EDP_LINK_TRAIN_400_600MV_0DB_SNB_B;
+	case DP_TRAIN_VOLTAGE_SWING_400 | DP_TRAIN_PRE_EMPHASIS_3_5:
+		return EDP_LINK_TRAIN_400MV_3_5DB_SNB_B;
 	case DP_TRAIN_VOLTAGE_SWING_400 | DP_TRAIN_PRE_EMPHASIS_6:
-		return EDP_LINK_TRAIN_400MV_6DB_SNB_B;
+	case DP_TRAIN_VOLTAGE_SWING_600 | DP_TRAIN_PRE_EMPHASIS_6:
+		return EDP_LINK_TRAIN_400_600MV_6DB_SNB_B;
 	case DP_TRAIN_VOLTAGE_SWING_600 | DP_TRAIN_PRE_EMPHASIS_3_5:
-		return EDP_LINK_TRAIN_600MV_3_5DB_SNB_B;
+	case DP_TRAIN_VOLTAGE_SWING_800 | DP_TRAIN_PRE_EMPHASIS_3_5:
+		return EDP_LINK_TRAIN_600_800MV_3_5DB_SNB_B;
 	case DP_TRAIN_VOLTAGE_SWING_800 | DP_TRAIN_PRE_EMPHASIS_0:
-		return EDP_LINK_TRAIN_800MV_0DB_SNB_B;
+	case DP_TRAIN_VOLTAGE_SWING_1200 | DP_TRAIN_PRE_EMPHASIS_0:
+		return EDP_LINK_TRAIN_800_1200MV_0DB_SNB_B;
 	default:
-		DRM_DEBUG_KMS("Unsupported voltage swing/pre-emphasis level\n");
-		return EDP_LINK_TRAIN_400MV_0DB_SNB_B;
+		DRM_DEBUG_KMS("Unsupported voltage swing/pre-emphasis level:"
+			      "0x%x\n", signal_levels);
+		return EDP_LINK_TRAIN_400_600MV_0DB_SNB_B;
 	}
 }