mailbox数据发送和接收的过程

我们知道在client 在通过mbox_send_message给controller发送数据的时候必须指定channel。例如下面的code
dc_sync->mbox =
(&dc_sync->cl, 0);
/* Populate data packet */
/* sp.abc = 123; etc */
/* Send message to remote in blocking mode */
mbox_send_message(dc_sync->mbox, &sp);
/* At this point 'sp' has been sent */
目前kernel提供了两种方法得到mailbox的channel
struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,const char *name);
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
使用完成后调用mbox_free_channel 释放channel，这样别人就可以继续使用这个channel
void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
其中mbox_request_channel_byname是mbox_request_channel的一个包装。所以这里直接看看mbox_request_channel
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
{
struct device *dev = cl->dev;
struct mbox_controller *mbox;
struct of_phandle_args spec;
struct mbox_chan *chan;
unsigned long flags;
int ret;

spin_lock_irqsave(&chan->lock, flags);
chan->msg_free = 0;
chan->msg_count = 0;
chan->active_req = NULL;
chan->cl = cl;
init_completion(&chan->tx_complete);

//初始化chan，并最终startup
ret = chan->mbox->ops->startup(chan);
if (ret) {
dev_err(dev, "Unable to startup the chan (%d)\n", ret);
mbox_free_channel(chan);
chan = ERR_PTR(ret);
}
}
以之前的arm_mhu.c 中定义的mbox_chan_ops为例
static const struct mbox_chan_ops mhu_ops = {
.send_data = mhu_send_data,
.startup = mhu_startup,
.shutdown = mhu_shutdown,
.last_tx_done = mhu_last_tx_done,
};

static int mhu_startup(struct mbox_chan *chan)
{
struct mhu_link *mlink = chan->con_priv;
u32 val;
int ret;

val = readl_relaxed(mlink->tx_reg + INTR_STAT_OFS);
writel_relaxed(val, mlink->tx_reg + INTR_CLR_OFS);
原来就是注册了一个中断，其回调函数是mhu_rx_interrupt
ret = request_irq(mlink->irq, mhu_rx_interrupt,
IRQF_SHARED, "mhu_link", chan);
if (ret) {
dev_err(chan->mbox->dev,
"Unable to acquire IRQ %d\n", mlink->irq);
return ret;
}

return 0;
}
这个中断函数如下：
当client 给controller 通过mbox_send_message发送数据后，arm_mhu 会产生一个中断给cotroller。
static irqreturn_t mhu_rx_interrupt(int irq, void *p)
{
struct mbox_chan *chan = p;
struct mhu_link *mlink = chan->con_priv;
u32 val;

val = readl_relaxed(mlink->rx_reg + INTR_STAT_OFS);
if (!val)
return IRQ_NONE;
controller调用mbox_chan_received_data 就可以得到client发送来的数据
mbox_chan_received_data(chan, (void *)&val);

writel_relaxed(val, mlink->rx_reg + INTR_CLR_OFS);

return IRQ_HANDLED;
}
void mbox_chan_received_data(struct mbox_chan *chan, void *mssg)
{
读去数据后，调用client的rx_callback 通知client
/* No buffering the received data */
if (chan->cl->rx_callback)
chan->cl->rx_callback(chan->cl, mssg);
}

controller接收数据的flow 清楚了，再看看client是如何调用mbox_send_message 发送数据的
mbox_send_message->msg_submit
if (chan->cl->tx_prepare)
chan->cl->tx_prepare(chan->cl, data);
/* 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--;
}
最终还是调用controll而的send_data 发送数据，本例controller的send_data函数为mhu_send_data
static int mhu_send_data(struct mbox_chan *chan, void *data)
{
struct mhu_link *mlink = chan->con_priv;
u32 *arg = data;
就是写controller的一个寄存器就行了，client写了之后后触发中断，controller会在中断中读到数据，并通过mbox_chan_received_data 通知client已经读取数据了
writel_relaxed(*arg, mlink->tx_reg + INTR_SET_OFS);

return 0;
}