drm/i915: Always program unique transition scale for CHV

The docs give you the impression that the unique transition scale
value shouldn't matter when unique transition scale is enabled. But
as Imre found on BXT (and I verfied also on BSW) the value does
matter. So from now on just program the same value 0x9a always.

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 26 insertions, 27 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index dcda86a7d68d..da7d1ae18b9b 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3179,6 +3179,12 @@ static uint32_t vlv_signal_levels(struct intel_dp *intel_dp)
 	return 0;
 }
 
+static bool chv_need_uniq_trans_scale(uint8_t train_set)
+{
+	return (train_set & DP_TRAIN_PRE_EMPHASIS_MASK) == DP_TRAIN_PRE_EMPH_LEVEL_0 &&
+		(train_set & DP_TRAIN_VOLTAGE_SWING_MASK) == DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
+}
+
 static uint32_t chv_signal_levels(struct intel_dp *intel_dp)
 {
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
@@ -3297,41 +3303,34 @@ static uint32_t chv_signal_levels(struct intel_dp *intel_dp)
 	/* Program swing margin */
 	for (i = 0; i < 4; i++) {
 		val = vlv_dpio_read(dev_priv, pipe, CHV_TX_DW2(ch, i));
+
 		val &= ~DPIO_SWING_MARGIN000_MASK;
 		val |= margin_reg_value << DPIO_SWING_MARGIN000_SHIFT;
+
+		/*
+		 * Supposedly this value shouldn't matter when unique transition
+		 * scale is disabled, but in fact it does matter. Let's just
+		 * always program the same value and hope it's OK.
+		 */
+		val &= ~(0xff << DPIO_UNIQ_TRANS_SCALE_SHIFT);
+		val |= 0x9a << DPIO_UNIQ_TRANS_SCALE_SHIFT;
+
 		vlv_dpio_write(dev_priv, pipe, CHV_TX_DW2(ch, i), val);
 	}
 
-	/* Disable unique transition scale */
+	/*
+	 * The document said it needs to set bit 27 for ch0 and bit 26
+	 * for ch1. Might be a typo in the doc.
+	 * For now, for this unique transition scale selection, set bit
+	 * 27 for ch0 and ch1.
+	 */
 	for (i = 0; i < 4; i++) {
 		val = vlv_dpio_read(dev_priv, pipe, CHV_TX_DW3(ch, i));
-		val &= ~DPIO_TX_UNIQ_TRANS_SCALE_EN;
-		vlv_dpio_write(dev_priv, pipe, CHV_TX_DW3(ch, i), val);
-	}
-
-	if (((train_set & DP_TRAIN_PRE_EMPHASIS_MASK)
-			== DP_TRAIN_PRE_EMPH_LEVEL_0) &&
-		((train_set & DP_TRAIN_VOLTAGE_SWING_MASK)
-			== DP_TRAIN_VOLTAGE_SWING_LEVEL_3)) {
-
-		/*
-		 * The document said it needs to set bit 27 for ch0 and bit 26
-		 * for ch1. Might be a typo in the doc.
-		 * For now, for this unique transition scale selection, set bit
-		 * 27 for ch0 and ch1.
-		 */
-		for (i = 0; i < 4; i++) {
-			val = vlv_dpio_read(dev_priv, pipe, CHV_TX_DW3(ch, i));
+		if (chv_need_uniq_trans_scale(train_set))
 			val |= DPIO_TX_UNIQ_TRANS_SCALE_EN;
-			vlv_dpio_write(dev_priv, pipe, CHV_TX_DW3(ch, i), val);
-		}
-
-		for (i = 0; i < 4; i++) {
-			val = vlv_dpio_read(dev_priv, pipe, CHV_TX_DW2(ch, i));
-			val &= ~(0xff << DPIO_UNIQ_TRANS_SCALE_SHIFT);
-			val |= (0x9a << DPIO_UNIQ_TRANS_SCALE_SHIFT);
-			vlv_dpio_write(dev_priv, pipe, CHV_TX_DW2(ch, i), val);
-		}
+		else
+			val &= ~DPIO_TX_UNIQ_TRANS_SCALE_EN;
+		vlv_dpio_write(dev_priv, pipe, CHV_TX_DW3(ch, i), val);
 	}
 
 	/* Start swing calculation */