drm/i915: Remove the broken DP CRC support for g4x

DP CRCs don't really work on g4x. If you want any CRCs on DP you must
select the CRC source before the port is enabled, otherwise the CRC
source select bits simply ignore any writes to them. And once the port
is enabled we mustn't change the CRC source select until the port is
disabled. That almost works, but not quite :( Eventually the CRC source
select bits get permanently stuck one way or the other, and after that
a reboot (or possibly a display reset) is needed to get working CRCs
on that pipe (not matter which CRC source we try to use).

Additionally the DFT scrambler reset bits we're trying to use don't
seem to exist on g4x. There are some potentially relevant looking bits
in the pipe registers, but when I tried it I got stable looking CRCs
without setting any bits for this.

If there is a way to make DP CRCs work reliably on g4x, I wasn't
able to find it. So let's just remove the broken code we have.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190214192219.3858-3-ville.syrjala@linux.intel.comReviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

drivers/gpu/drm/i915/intel_pipe_crc.c

@@ -191,8 +191,6 @@ static int i9xx_pipe_crc_ctl_reg(struct drm_i915_private *dev_priv,
 				 enum intel_pipe_crc_source *source,
 				 u32 *val)
 {
-	bool need_stable_symbols = false;
-
 	if (*source == INTEL_PIPE_CRC_SOURCE_AUTO) {
 		int ret = i9xx_pipe_crc_auto_source(dev_priv, pipe, source);
 		if (ret)
@@ -208,56 +206,23 @@ static int i9xx_pipe_crc_ctl_reg(struct drm_i915_private *dev_priv,
 			return -EINVAL;
 		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_TV_PRE;
 		break;
-	case INTEL_PIPE_CRC_SOURCE_DP_B:
-		if (!IS_G4X(dev_priv))
-			return -EINVAL;
-		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_DP_B_G4X;
-		need_stable_symbols = true;
-		break;
-	case INTEL_PIPE_CRC_SOURCE_DP_C:
-		if (!IS_G4X(dev_priv))
-			return -EINVAL;
-		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_DP_C_G4X;
-		need_stable_symbols = true;
-		break;
-	case INTEL_PIPE_CRC_SOURCE_DP_D:
-		if (!IS_G4X(dev_priv))
-			return -EINVAL;
-		*val = PIPE_CRC_ENABLE | PIPE_CRC_SOURCE_DP_D_G4X;
-		need_stable_symbols = true;
-		break;
 	case INTEL_PIPE_CRC_SOURCE_NONE:
 		*val = 0;
 		break;
 	default:
+		/*
+		 * The DP CRC source doesn't work on g4x.
+		 * It can be made to work to some degree by selecting
+		 * the correct CRC source before the port is enabled,
+		 * and not touching the CRC source bits again until
+		 * the port is disabled. But even then the bits
+		 * eventually get stuck and a reboot is needed to get
+		 * working CRCs on the pipe again. Let's simply
+		 * refuse to use DP CRCs on g4x.
+		 */
 		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) {
-		u32 tmp = I915_READ(PORT_DFT2_G4X);
-
-		WARN_ON(!IS_G4X(dev_priv));
-
-		I915_WRITE(PORT_DFT_I9XX,
-			   I915_READ(PORT_DFT_I9XX) | DC_BALANCE_RESET);
-
-		if (pipe == PIPE_A)
-			tmp |= PIPE_A_SCRAMBLE_RESET;
-		else
-			tmp |= PIPE_B_SCRAMBLE_RESET;
-
-		I915_WRITE(PORT_DFT2_G4X, tmp);
-	}
-
 	return 0;
 }
 
@@ -282,24 +247,6 @@ static void vlv_undo_pipe_scramble_reset(struct drm_i915_private *dev_priv,
 	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_i915_private *dev_priv,
-					 enum pipe pipe)
-{
-	u32 tmp = I915_READ(PORT_DFT2_G4X);
-
-	if (pipe == PIPE_A)
-		tmp &= ~PIPE_A_SCRAMBLE_RESET;
-	else
-		tmp &= ~PIPE_B_SCRAMBLE_RESET;
-	I915_WRITE(PORT_DFT2_G4X, tmp);
-
-	if (!(tmp & PIPE_SCRAMBLE_RESET_MASK)) {
-		I915_WRITE(PORT_DFT_I9XX,
-			   I915_READ(PORT_DFT_I9XX) & ~DC_BALANCE_RESET);
-	}
 }
 
 static int ilk_pipe_crc_ctl_reg(enum intel_pipe_crc_source *source,
@@ -485,9 +432,6 @@ static int i9xx_crc_source_valid(struct drm_i915_private *dev_priv,
 	switch (source) {
 	case INTEL_PIPE_CRC_SOURCE_PIPE:
 	case INTEL_PIPE_CRC_SOURCE_TV:
-	case INTEL_PIPE_CRC_SOURCE_DP_B:
-	case INTEL_PIPE_CRC_SOURCE_DP_C:
-	case INTEL_PIPE_CRC_SOURCE_DP_D:
 	case INTEL_PIPE_CRC_SOURCE_NONE:
 		return 0;
 	default:
@@ -612,9 +556,7 @@ int intel_crtc_set_crc_source(struct drm_crtc *crtc, const char *source_name)
 	POSTING_READ(PIPE_CRC_CTL(crtc->index));
 
 	if (!source) {
-		if (IS_G4X(dev_priv))
-			g4x_undo_pipe_scramble_reset(dev_priv, crtc->index);
-		else if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
+		if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 			vlv_undo_pipe_scramble_reset(dev_priv, crtc->index);
 		else if ((IS_HASWELL(dev_priv) ||
 			  IS_BROADWELL(dev_priv)) && crtc->index == PIPE_A)