smn_read_register
return read_poll_timeout(smn_read_register, data, data > 0, DELAY_US,
ret = read_poll_timeout(smn_read_register, data, data > 0 && data & MBOX_READY_MASK,
ret = read_poll_timeout(smn_read_register, data, data > 0, MBOX_DELAY_US,