drm/i915/hdcp: Mandate (seq_num_V==0) at first RecvId msg

HDCP Repeater initializes seq_num_V to 0 at the beginning of
hdcp Session i.e. after AKE_init received, refer
HDCP 2.2 Spec HDMI PAGE 19, DP PAGE 20.

HDCP 2.2 Comp specs 1B-06 test verifies that whether DUT
considers failure of authentication if the repeater provides a
non-zero value in seq_num_V in the first,
RepeaterAuth_Send_ReceiverID_List message.

Make sure that HDCP repeater initializes seq_num_V to zero at
beginning of session i.e. after AKE_Init, fail the Auth if
there is non zero seq_num_V.

v2:
- Used existing hdcp2_encrypted flag instead of
  declaring new flag. [Ram]

Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200220123217.23635-2-anshuman.gupta@intel.com

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

@@ -1470,6 +1470,12 @@ int hdcp2_authenticate_repeater_topology(struct intel_connector *connector)
 	seq_num_v =
 		drm_hdcp_be24_to_cpu((const u8 *)msgs.recvid_list.seq_num_v);
 
+	if (!hdcp->hdcp2_encrypted && seq_num_v) {
+		drm_dbg_kms(&dev_priv->drm,
+			    "Non zero Seq_num_v at first RecvId_List msg\n");
+		return -EINVAL;
+	}
+
 	if (seq_num_v < hdcp->seq_num_v) {
 		/* Roll over of the seq_num_v from repeater. Reauthenticate. */
 		drm_dbg_kms(&dev_priv->drm, "Seq_num_v roll over.\n");