drm/i915: scramble reset support for DP port CRC on vlv

They've moved the DC balance reset bit around. Again I don't think we
need it, but better safe than sorry and maybe HDMI port CRC will prove
useful for checking infoframes or hdmi audio.

v2: Apply the suggestions from Damien's review.
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2026,6 +2026,9 @@ static int vlv_pipe_crc_ctl_reg(struct drm_device *dev,
 				enum intel_pipe_crc_source *source,
 				uint32_t *val)
 {
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	bool need_stable_symbols = false;
+
 	if (*source == INTEL_PIPE_CRC_SOURCE_AUTO) {
 		int ret = i9xx_pipe_crc_auto_source(dev, pipe, source);
 		if (ret)
@@ -2038,9 +2041,11 @@ static int vlv_pipe_crc_ctl_reg(struct drm_device *dev,
 		break;
 	case INTEL_PIPE_CRC_SOURCE_DP_B:
 		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_DP_B_VLV;
+		need_stable_symbols = true;
 		break;
 	case INTEL_PIPE_CRC_SOURCE_DP_C:
 		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_DP_C_VLV;
+		need_stable_symbols = true;
 		break;
 	case INTEL_PIPE_CRC_SOURCE_NONE:
 		*val = 0;
@@ -2049,6 +2054,29 @@ static int vlv_pipe_crc_ctl_reg(struct drm_device *dev,
 		return -EINVAL;
 	}
 
+	/*
+	 * When the pipe CRC tap point is after the transcoders we need
+	 * to tweak symbol-level features to produce a deterministic series of
+	 * symbols for a given frame. We need to reset those features only once
+	 * a frame (instead of every nth symbol):
+	 *   - DC-balance: used to ensure a better clock recovery from the data
+	 *     link (SDVO)
+	 *   - DisplayPort scrambling: used for EMI reduction
+	 */
+	if (need_stable_symbols) {
+		uint32_t tmp = I915_READ(PORT_DFT2_G4X);
+
+		WARN_ON(!IS_G4X(dev));
+
+		tmp |= DC_BALANCE_RESET_VLV;
+		if (pipe == PIPE_A)
+			tmp |= PIPE_A_SCRAMBLE_RESET;
+		else
+			tmp |= PIPE_B_SCRAMBLE_RESET;
+
+		I915_WRITE(PORT_DFT2_G4X, tmp);
+	}
+
 	return 0;
 }
 
@@ -2128,6 +2156,22 @@ static int i9xx_pipe_crc_ctl_reg(struct drm_device *dev,
 	return 0;
 }
 
+static void vlv_undo_pipe_scramble_reset(struct drm_device *dev,
+					 enum pipe pipe)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t tmp = I915_READ(PORT_DFT2_G4X);
+
+	if (pipe == PIPE_A)
+		tmp &= ~PIPE_A_SCRAMBLE_RESET;
+	else
+		tmp &= ~PIPE_B_SCRAMBLE_RESET;
+	if (!(tmp & PIPE_SCRAMBLE_RESET_MASK))
+		tmp &= ~DC_BALANCE_RESET_VLV;
+	I915_WRITE(PORT_DFT2_G4X, tmp);
+
+}
+
 static void g4x_undo_pipe_scramble_reset(struct drm_device *dev,
 					 enum pipe pipe)
 {
@@ -2267,6 +2311,8 @@ static int pipe_crc_set_source(struct drm_device *dev, enum pipe pipe,
 
 		if (IS_G4X(dev))
 			g4x_undo_pipe_scramble_reset(dev, pipe);
+		else if (IS_VALLEYVIEW(dev))
+			vlv_undo_pipe_scramble_reset(dev, pipe);
 	}
 
 	return 0;