fm10k_fifo_head_offset
msg = fifo->buffer + fm10k_fifo_head_offset(fifo, len);
end = fm10k_fifo_head_offset(fifo, mbx->pulled);
head = fm10k_fifo_head_offset(&mbx->tx, mbx->pulled);
u32 *head = fifo->buffer + fm10k_fifo_head_offset(fifo, 0);
crc = fm10k_fifo_crc(fifo, fm10k_fifo_head_offset(fifo, mbx->pulled),