diff --git a/sys/cam/cam_sim.c b/sys/cam/cam_sim.c
index e7a7348d0c44..abf65965fc8e 100644
--- a/sys/cam/cam_sim.c
+++ b/sys/cam/cam_sim.c
@@ -127,6 +127,19 @@ cam_sim_alloc(sim_action_func sim_action, sim_poll_func sim_poll,
 	return (sim);
 }
 
+/**
+ * @brief frees up the sim
+ *
+ * Frees up the CAM @c sim and optionally the devq. If a mutex is associated
+ * with the sim, it must be locked on entry. It will remain locked on
+ * return.
+ *
+ * This function will wait for all outstanding reference to the sim to clear
+ * before returning.
+ *
+ * @param sim          The sim to free
+ * @param free_devq    Free the devq associated with the sim at creation.
+ */
 void
 cam_sim_free(struct cam_sim *sim, int free_devq)
 {