drm/i915: HDCP: retry link integrity check on failure

A single Ri mismatch doesn't automatically mean that the link integrity
is broken. Update and check of Ri and Ri' are done asynchronously. In
case an update happens just between the read of Ri' and the check against
Ri there will be a mismatch even if the link integrity is fine otherwise.
Signed-off-by: Oliver Barta <oliver.barta@aptiv.com>
Reviewed-by: Sean Paul <sean@poorly.run>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200504123524.7731-1-oliver.barta@aptiv.com

drivers/gpu/drm/i915/display/intel_hdmi.c

@@ -1540,7 +1540,7 @@ int intel_hdmi_hdcp_toggle_signalling(struct intel_digital_port *intel_dig_port,
 }
 
 static
-bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
+bool intel_hdmi_hdcp_check_link_once(struct intel_digital_port *intel_dig_port)
 {
 	struct drm_i915_private *i915 = to_i915(intel_dig_port->base.base.dev);
 	struct intel_connector *connector =
@@ -1563,8 +1563,7 @@ bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
 	if (wait_for((intel_de_read(i915, HDCP_STATUS(i915, cpu_transcoder, port)) &
 		      (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC)) ==
 		     (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1)) {
-		drm_err(&i915->drm,
-			"Ri' mismatch detected, link check failed (%x)\n",
+		drm_dbg_kms(&i915->drm, "Ri' mismatch detected (%x)\n",
 			intel_de_read(i915, HDCP_STATUS(i915, cpu_transcoder,
 							port)));
 		return false;
@@ -1572,6 +1571,20 @@ bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
 	return true;
 }
 
+static
+bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
+{
+	struct drm_i915_private *i915 = to_i915(intel_dig_port->base.base.dev);
+	int retry;
+
+	for (retry = 0; retry < 3; retry++)
+		if (intel_hdmi_hdcp_check_link_once(intel_dig_port))
+			return true;
+
+	drm_err(&i915->drm, "Link check failed\n");
+	return false;
+}
+
 struct hdcp2_hdmi_msg_timeout {
 	u8 msg_id;
 	u16 timeout;