drm/i915: Simplify the way BC bifurcation state consistency is kept

Remove the global modeset resource function that would disable the
bifurcation bit, and instead enable/disable it when enabling the pch
transcoder. The mode set consistency check should prevent us from
disabling the bit if pipe C is enabled so the change should be safe.

Note that this doens't affect the logic that prevents the bit being
set while a pipe is active, since the patch retains the behavior of
only chaging the bit if necessary. Because of the checks during mode
set, the first change would necessarily happen with both pipes B and
C disabled, and any subsequent write would be skipped.

v2: Only change the bit during pch trancoder enable. (Ville)
Signed-off-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3147,32 +3147,6 @@ static bool pipe_has_enabled_pch(struct intel_crtc *crtc)
 		crtc->config->has_pch_encoder;
 }
 
-static void ivb_modeset_global_resources(struct drm_device *dev)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_crtc *pipe_B_crtc =
-		to_intel_crtc(dev_priv->pipe_to_crtc_mapping[PIPE_B]);
-	struct intel_crtc *pipe_C_crtc =
-		to_intel_crtc(dev_priv->pipe_to_crtc_mapping[PIPE_C]);
-	uint32_t temp;
-
-	/*
-	 * When everything is off disable fdi C so that we could enable fdi B
-	 * with all lanes. Note that we don't care about enabled pipes without
-	 * an enabled pch encoder.
-	 */
-	if (!pipe_has_enabled_pch(pipe_B_crtc) &&
-	    !pipe_has_enabled_pch(pipe_C_crtc)) {
-		WARN_ON(I915_READ(FDI_RX_CTL(PIPE_B)) & FDI_RX_ENABLE);
-		WARN_ON(I915_READ(FDI_RX_CTL(PIPE_C)) & FDI_RX_ENABLE);
-
-		temp = I915_READ(SOUTH_CHICKEN1);
-		temp &= ~FDI_BC_BIFURCATION_SELECT;
-		DRM_DEBUG_KMS("disabling fdi C rx\n");
-		I915_WRITE(SOUTH_CHICKEN1, temp);
-	}
-}
-
 /* The FDI link training functions for ILK/Ibexpeak. */
 static void ironlake_fdi_link_train(struct drm_crtc *crtc)
 {
@@ -3828,20 +3802,23 @@ static void ironlake_pch_transcoder_set_timings(struct intel_crtc *crtc,
 		   I915_READ(VSYNCSHIFT(cpu_transcoder)));
 }
 
-static void cpt_enable_fdi_bc_bifurcation(struct drm_device *dev)
+static void cpt_set_fdi_bc_bifurcation(struct drm_device *dev, bool enable)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	uint32_t temp;
 
 	temp = I915_READ(SOUTH_CHICKEN1);
-	if (temp & FDI_BC_BIFURCATION_SELECT)
+	if (!!(temp & FDI_BC_BIFURCATION_SELECT) == enable)
 		return;
 
 	WARN_ON(I915_READ(FDI_RX_CTL(PIPE_B)) & FDI_RX_ENABLE);
 	WARN_ON(I915_READ(FDI_RX_CTL(PIPE_C)) & FDI_RX_ENABLE);
 
-	temp |= FDI_BC_BIFURCATION_SELECT;
-	DRM_DEBUG_KMS("enabling fdi C rx\n");
+	temp &= ~FDI_BC_BIFURCATION_SELECT;
+	if (enable)
+		temp |= FDI_BC_BIFURCATION_SELECT;
+
+	DRM_DEBUG_KMS("%sabling fdi C rx\n", enable ? "en" : "dis");
 	I915_WRITE(SOUTH_CHICKEN1, temp);
 	POSTING_READ(SOUTH_CHICKEN1);
 }
@@ -3849,20 +3826,19 @@ static void cpt_enable_fdi_bc_bifurcation(struct drm_device *dev)
 static void ivybridge_update_fdi_bc_bifurcation(struct intel_crtc *intel_crtc)
 {
 	struct drm_device *dev = intel_crtc->base.dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	switch (intel_crtc->pipe) {
 	case PIPE_A:
 		break;
 	case PIPE_B:
 		if (intel_crtc->config->fdi_lanes > 2)
-			WARN_ON(I915_READ(SOUTH_CHICKEN1) & FDI_BC_BIFURCATION_SELECT);
+			cpt_set_fdi_bc_bifurcation(dev, false);
 		else
-			cpt_enable_fdi_bc_bifurcation(dev);
+			cpt_set_fdi_bc_bifurcation(dev, true);
 
 		break;
 	case PIPE_C:
-		cpt_enable_fdi_bc_bifurcation(dev);
+		cpt_set_fdi_bc_bifurcation(dev, true);
 
 		break;
 	default:
@@ -13141,8 +13117,6 @@ static void intel_init_display(struct drm_device *dev)
 	} else if (IS_IVYBRIDGE(dev)) {
 		/* FIXME: detect B0+ stepping and use auto training */
 		dev_priv->display.fdi_link_train = ivb_manual_fdi_link_train;
-		dev_priv->display.modeset_global_resources =
-			ivb_modeset_global_resources;
 	} else if (IS_HASWELL(dev) || IS_BROADWELL(dev)) {
 		dev_priv->display.fdi_link_train = hsw_fdi_link_train;
 	} else if (IS_VALLEYVIEW(dev)) {