diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index b4505d55990d6ba4dcf9e479dd45b0810fe06191..fe25a01c81f22661cb5c8a7d3db34a7851e579b3 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1511,6 +1511,11 @@ struct drm_i915_perf_oa_config {
 	__u32 n_boolean_regs;
 	__u32 n_flex_regs;
 
+	/*
+	 * These fields are pointers to tuples of u32 values (register
+	 * address, value). For example the expected length of the buffer
+	 * pointed by mux_regs_ptr is (2 * sizeof(u32) * n_mux_regs).
+	 */
 	__u64 mux_regs_ptr;
 	__u64 boolean_regs_ptr;
 	__u64 flex_regs_ptr;