drm/i915: Check for downstream topology errors

HDCP compliant Repeaters can support max of 127 devices and max
depth of 7 for downstream topology.

If these max limits are exceeded, repeater will set the
topology error flags MAX_CASCADE_EXCEEDED and/or MAX_DEVS_EXCEEDED
in Bstatus followed by asserting READY/CP_IRQ for HDCP transmitter.

This patch check for these error flags as soon as READY bit is asserted.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
[seanpaul fixed checkpatch alignment issue]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1516254488-4971-5-git-send-email-ramalingam.c@intel.com

drivers/gpu/drm/i915/intel_hdcp.c

@@ -160,6 +160,12 @@ int intel_hdcp_auth_downstream(struct intel_digital_port *intel_dig_port,
 	if (ret)
 		return ret;
 
+	if (DRM_HDCP_MAX_DEVICE_EXCEEDED(bstatus[0]) ||
+	    DRM_HDCP_MAX_CASCADE_EXCEEDED(bstatus[1])) {
+		DRM_ERROR("Max Topology Limit Exceeded\n");
+		return -EPERM;
+	}
+
 	/* If there are no downstream devices, we're all done. */
 	num_downstream = DRM_HDCP_NUM_DOWNSTREAM(bstatus[0]);
 	if (num_downstream == 0) {

include/drm/drm_hdcp.h

@@ -20,6 +20,8 @@
 #define DRM_HDCP_V_PRIME_PART_LEN		4
 #define DRM_HDCP_V_PRIME_NUM_PARTS		5
 #define DRM_HDCP_NUM_DOWNSTREAM(x)		(x & 0x3f)
+#define DRM_HDCP_MAX_CASCADE_EXCEEDED(x)	(x & BIT(3))
+#define DRM_HDCP_MAX_DEVICE_EXCEEDED(x)		(x & BIT(7))
 
 /* Slave address for the HDCP registers in the receiver */
 #define DRM_HDCP_DDC_ADDR			0x3A