只罗列增加取走消息：

static int add_to_rbuf(struct mbox_chan *chan, void *mssg){    int idx;    unsigned long flags;    spin_lock_irqsave(&chan->lock, flags);    /* See if there is any space left */    if (chan->msg_count == MBOX_TX_QUEUE_LEN) {        spin_unlock_irqrestore(&chan->lock, flags);        return -ENOBUFS;    }    idx = chan->msg_free;    chan->msg_data[idx] = mssg;    chan->msg_count++;    if (idx == MBOX_TX_QUEUE_LEN - 1)        chan->msg_free = 0;    else        chan->msg_free++;    spin_unlock_irqrestore(&chan->lock, flags);    return idx;}static void msg_submit(struct mbox_chan *chan){    unsigned count, idx;    unsigned long flags;    void *data;    int err;    spin_lock_irqsave(&chan->lock, flags);    if (!chan->msg_count || chan->active_req)        goto exit;    count = chan->msg_count;    idx = chan->msg_free;    if (idx >= count)        idx -= count;    else        idx += MBOX_TX_QUEUE_LEN - count;    data = chan->msg_data[idx];    /* Try to submit a message to the MBOX controller */    err = chan->mbox->ops->send_data(chan, data);    if (!err) {        chan->active_req = data;        chan->msg_count--;    }exit:    spin_unlock_irqrestore(&chan->lock, flags);}