drm/i915: Fix KBL HDCP2.2 encrypt status signalling

HDCP transmitter is supposed to indicate the HDCP encryption status of
the link through enc_en signals in a window of time called "window of
opportunity" defined by HDCP HDMI spec.

But on KBL this timing of signalling has an issue. To fix the issue this
WA of resetting the signalling is required.

v2:
  WA is moved into the toggle_signalling [Daniel]
v3:
  Commit msg is rewritten with more information
v4:
  Reviewed-by Daniel.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1550338640-17470-17-git-send-email-ramalingam.c@intel.com

drivers/gpu/drm/i915/intel_hdmi.c

@@ -1083,10 +1083,44 @@ int intel_hdmi_hdcp_read_v_prime_part(struct intel_digital_port *intel_dig_port,
 	return ret;
 }
 
+static int kbl_repositioning_enc_en_signal(struct intel_connector *connector)
+{
+	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
+	struct intel_digital_port *intel_dig_port = conn_to_dig_port(connector);
+	struct drm_crtc *crtc = connector->base.state->crtc;
+	struct intel_crtc *intel_crtc = container_of(crtc,
+						     struct intel_crtc, base);
+	u32 scanline;
+	int ret;
+
+	for (;;) {
+		scanline = I915_READ(PIPEDSL(intel_crtc->pipe));
+		if (scanline > 100 && scanline < 200)
+			break;
+		usleep_range(25, 50);
+	}
+
+	ret = intel_ddi_toggle_hdcp_signalling(&intel_dig_port->base, false);
+	if (ret) {
+		DRM_ERROR("Disable HDCP signalling failed (%d)\n", ret);
+		return ret;
+	}
+	ret = intel_ddi_toggle_hdcp_signalling(&intel_dig_port->base, true);
+	if (ret) {
+		DRM_ERROR("Enable HDCP signalling failed (%d)\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
 static
 int intel_hdmi_hdcp_toggle_signalling(struct intel_digital_port *intel_dig_port,
 				      bool enable)
 {
+	struct intel_hdmi *hdmi = &intel_dig_port->hdmi;
+	struct intel_connector *connector = hdmi->attached_connector;
+	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	int ret;
 
 	if (!enable)
@@ -1098,6 +1132,14 @@ int intel_hdmi_hdcp_toggle_signalling(struct intel_digital_port *intel_dig_port,
 			  enable ? "Enable" : "Disable", ret);
 		return ret;
 	}
+
+	/*
+	 * WA: To fix incorrect positioning of the window of
+	 * opportunity and enc_en signalling in KABYLAKE.
+	 */
+	if (IS_KABYLAKE(dev_priv) && enable)
+		return kbl_repositioning_enc_en_signal(connector);
+
 	return 0;
 }