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>

1 files changed, 46 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 881251611512..82c58eb1aa66 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/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;