mailbox的controller

mailbox是kernel提供的一种板子上的硬件和soc通过messages queue，interrupt 进行通讯的一个架构。正式版的英文翻译如下：
menuconfig MAILBOX
	bool "Mailbox Hardware Support"
	help
	  Mailbox is a framework to control hardware communication between
	  on-chip processors through queued messages and interrupt driven
	  signals. Say Y if your platform supports hardware mailboxes.
mailbox的实现分为contoller和client。简单的说就是clinet 可以通过controller提供的channle发送信息给conroller
因此在drivers/mailbox下实现的都是controller的源码
具体到某个厂商的硬件，则描述如下：
config ARM_MHU
    tristate "ARM MHU Mailbox"
    depends on ARM_AMBA
    help
      Say Y here if you want to build the ARM MHU controller driver.
      The controller has 3 mailbox channels, the last of which can be
      used in Secure mode only.
通过makefile我们知道要实现mailbox的源文件其实只有两个
obj-$(CONFIG_MAILBOX)		+= mailbox.o
obj-$(CONFIG_ARM_MHU)	+= arm_mhu.o
其中mailbox.c 是kernel提供的framework，arm_mhu.c 则是具体厂商的实现
这里直接看arm_mhu.c的probe函数
static int mhu_probe(struct amba_device *adev, const struct amba_id *id)
{
	int i, err;
	struct arm_mhu *mhu;
	struct device *dev = &adev->dev;
	int mhu_reg[MHU_CHANS] = {MHU_LP_OFFSET, MHU_HP_OFFSET, MHU_SEC_OFFSET};

	/* Allocate memory for device */
	mhu = devm_kzalloc(dev, sizeof(*mhu), GFP_KERNEL);
	if (!mhu)
		return -ENOMEM;

	mhu->base = devm_ioremap_resource(dev, &adev->res);
	if (IS_ERR(mhu->base)) {
		dev_err(dev, "ioremap failed\n");
		return PTR_ERR(mhu->base);
	}
//mailbox的channel 表示可以发送信息的寄存器
	for (i = 0; i < MHU_CHANS; i++) {
		mhu->chan[i].con_priv = &mhu->mlink[i];
		mhu->mlink[i].irq = adev->irq[i];
		mhu->mlink[i].rx_reg = mhu->base + mhu_reg[i];
		mhu->mlink[i].tx_reg = mhu->mlink[i].rx_reg + TX_REG_OFFSET;
	}
//初始化mbox的结构体
	mhu->mbox.dev = dev;
	mhu->mbox.chans = &mhu->chan[0];
	mhu->mbox.num_chans = MHU_CHANS;
//mbox.ops 表示mailbox这个硬件具体的操作，例如发送数据，初始化等
	mhu->mbox.ops = &mhu_ops;
//发送数据采用poll的方式
	mhu->mbox.txdone_irq = false;
	mhu->mbox.txdone_poll = true;
	mhu->mbox.txpoll_period = 1;

	amba_set_drvdata(adev, mhu);
//所有的controller 最终都要通过mbox_controller_register 来注册自己
	err = mbox_controller_register(&mhu->mbox);
	if (err) {
		dev_err(dev, "Failed to register mailboxes %d\n", err);
		return err;
	}

	dev_info(dev, "ARM MHU Mailbox registered\n");
	return 0;
}

int mbox_controller_register(struct mbox_controller *mbox)
{
	int i, txdone;
//下面这四个任何一个为null，就退出注册
	/* Sanity check */
	if (!mbox || !mbox->dev || !mbox->ops || !mbox->num_chans)
		return -EINVAL;
//client发送数据是通过poll的方式还是irq的方式，后面针对两种方式有不同的处理方式
	if (mbox->txdone_irq)
		txdone = TXDONE_BY_IRQ;
	else if (mbox->txdone_poll)
		txdone = TXDONE_BY_POLL;
	else /* It has to be ACK then */
		txdone = TXDONE_BY_ACK;
//如果是poll的方式，则注册一个timer，定时查询
	if (txdone == TXDONE_BY_POLL) {

		if (!mbox->ops->last_tx_done) {
			dev_err(mbox->dev, "last_tx_done method is absent\n");
			return -EINVAL;
		}

		hrtimer_init(&mbox->poll_hrt, CLOCK_MONOTONIC,
			     HRTIMER_MODE_REL);
		mbox->poll_hrt.function = txdone_hrtimer;
	}
//初始化controller的channel，表示contoller 同时能尽量几路信息的传递
	for (i = 0; i < mbox->num_chans; i++) {
		struct mbox_chan *chan = &mbox->chans[i];

		chan->cl = NULL;
		chan->mbox = mbox;
		chan->txdone_method = txdone;
		spin_lock_init(&chan->lock);
	}

	if (!mbox->of_xlate)
		mbox->of_xlate = of_mbox_index_xlate;
//所有的mailbox最终都会添加到mbox_cons 这个list中
	mutex_lock(&con_mutex);
	list_add_tail(&mbox->node, &mbox_cons);
	mutex_unlock(&con_mutex);

	return 0;
}