+ /* In theory multiple mdio_mux could be stacked, thus creating
+ * more than a single level of nesting. But in practice,
+ * SINGLE_DEPTH_NESTING will cover the vast majority of use
+ * cases. We use it, instead of trying to handle the general
+ * case.
+ */
+ mutex_lock_nested(&pb->mii_bus->mdio_lock, SINGLE_DEPTH_NESTING);