drm/i915: Engage the DP scramble reset for pipe C on CHV

To get stable CRCs from the DP CRC source we need to reset the
scrambler for each frame. Enable the reset feature when grabbing
CRCs for pipe C on CHV. Pipes A and B were already covered due
sharing the code with VLV.

We can safely extend PIPE_SCRAMBLE_RESET_MASK to deal with CHV since
the extra bit was MBZ on the older platforms.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -3120,11 +3120,19 @@ static int vlv_pipe_crc_ctl_reg(struct drm_device *dev,
 		uint32_t tmp = I915_READ(PORT_DFT2_G4X);
 
 		tmp |= DC_BALANCE_RESET_VLV;
-		if (pipe == PIPE_A)
+		switch (pipe) {
+		case PIPE_A:
 			tmp |= PIPE_A_SCRAMBLE_RESET;
-		else
+			break;
+		case PIPE_B:
 			tmp |= PIPE_B_SCRAMBLE_RESET;
-
+			break;
+		case PIPE_C:
+			tmp |= PIPE_C_SCRAMBLE_RESET;
+			break;
+		default:
+			return -EINVAL;
+		}
 		I915_WRITE(PORT_DFT2_G4X, tmp);
 	}
 
@@ -3213,10 +3221,19 @@ static void vlv_undo_pipe_scramble_reset(struct drm_device *dev,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	uint32_t tmp = I915_READ(PORT_DFT2_G4X);
 
-	if (pipe == PIPE_A)
+	switch (pipe) {
+	case PIPE_A:
 		tmp &= ~PIPE_A_SCRAMBLE_RESET;
-	else
+		break;
+	case PIPE_B:
 		tmp &= ~PIPE_B_SCRAMBLE_RESET;
+		break;
+	case PIPE_C:
+		tmp &= ~PIPE_C_SCRAMBLE_RESET;
+		break;
+	default:
+		return;
+	}
 	if (!(tmp & PIPE_SCRAMBLE_RESET_MASK))
 		tmp &= ~DC_BALANCE_RESET_VLV;
 	I915_WRITE(PORT_DFT2_G4X, tmp);

drivers/gpu/drm/i915/i915_reg.h

@@ -2789,7 +2789,8 @@ enum punit_power_well {
 #define   DC_BALANCE_RESET			(1 << 25)
 #define PORT_DFT2_G4X		(dev_priv->info.display_mmio_offset + 0x61154)
 #define   DC_BALANCE_RESET_VLV			(1 << 31)
-#define   PIPE_SCRAMBLE_RESET_MASK		(0x3 << 0)
+#define   PIPE_SCRAMBLE_RESET_MASK		((1 << 14) | (0x3 << 0))
+#define   PIPE_C_SCRAMBLE_RESET			(1 << 14) /* chv */
 #define   PIPE_B_SCRAMBLE_RESET			(1 << 1)
 #define   PIPE_A_SCRAMBLE_RESET			(1 << 0)