drm/amd/display: avoid to authentication when DEVICE_COUNT=0

[why]
we don't support authentication with DEVICE_COUNT=0

[how]
check value DEVICE_COUNT before doing authentication
Signed-off-by: Yu-ting Shen <Yu-ting.Shen@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Wayne Lin <waynelin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c

@@ -128,6 +128,11 @@ static inline uint8_t get_device_count(struct mod_hdcp *hdcp)
 
 static inline enum mod_hdcp_status check_device_count(struct mod_hdcp *hdcp)
 {
+	/* Avoid device count == 0 to do authentication */
+	if (0 == get_device_count(hdcp)) {
+		return MOD_HDCP_STATUS_HDCP1_DEVICE_COUNT_MISMATCH_FAILURE;
+	}
+
 	/* Some MST display may choose to report the internal panel as an HDCP RX.
 	 * To update this condition with 1(because the immediate repeater's internal
 	 * panel is possibly not included in DEVICE_COUNT) + get_device_count(hdcp).

drivers/gpu/drm/amd/display/modules/hdcp/hdcp2_execution.c

@@ -207,6 +207,11 @@ static inline uint8_t get_device_count(struct mod_hdcp *hdcp)
 
 static enum mod_hdcp_status check_device_count(struct mod_hdcp *hdcp)
 {
+	/* Avoid device count == 0 to do authentication */
+	if (0 == get_device_count(hdcp)) {
+		return MOD_HDCP_STATUS_HDCP1_DEVICE_COUNT_MISMATCH_FAILURE;
+	}
+
 	/* Some MST display may choose to report the internal panel as an HDCP RX.   */
 	/* To update this condition with 1(because the immediate repeater's internal */
 	/* panel is possibly not included in DEVICE_COUNT) + get_device_count(hdcp). */