diff --git a/drivers/gpu/drm/radeon/r600_hdmi.c b/drivers/gpu/drm/radeon/r600_hdmi.c
index e2ae1c237fb4..5b729319f27b 100644
--- a/drivers/gpu/drm/radeon/r600_hdmi.c
+++ b/drivers/gpu/drm/radeon/r600_hdmi.c
@@ -451,6 +451,7 @@ void r600_hdmi_setmode(struct drm_encoder *encoder, struct drm_display_mode *mod
 	}
 
 	WREG32(HDMI0_ACR_PACKET_CONTROL + offset,
+	       HDMI0_ACR_SOURCE | /* select SW CTS value - XXX verify that hw CTS works on all families */
 	       HDMI0_ACR_AUTO_SEND); /* allow hw to sent ACR packets when required */
 
 	WREG32(HDMI0_VBI_PACKET_CONTROL + offset,