diff --git a/include/drm/amdgpu_drm.h b/include/drm/amdgpu_drm.h
index 7f01f983..c0a0ad10 100644
--- a/include/drm/amdgpu_drm.h
+++ b/include/drm/amdgpu_drm.h
@@ -553,6 +553,10 @@ struct drm_amdgpu_gem_va {
 #define AMDGPU_HW_IP_VCE          4
 #define AMDGPU_HW_IP_UVD_ENC      5
 #define AMDGPU_HW_IP_VCN_DEC      6
+/*
+ * From VCN4, AMDGPU_HW_IP_VCN_ENC is re-used to support
+ * both encoding and decoding jobs.
+ */
 #define AMDGPU_HW_IP_VCN_ENC      7
 #define AMDGPU_HW_IP_VCN_JPEG     8
 #define AMDGPU_HW_IP_NUM          9