1 概述

(1)mailbox是一种框架，通过消息队列和中断驱动信号处理多处理器间的通讯；

(2)mailbox的实现分为contoller和client。简单的说就是client 可以通过controller提供的channel发送信息给controller；

(3)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：

Kconfig文件：内核开关，用于配置mbox模块是否编译到内核；

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.

Makefile文件：根据Kconfig编译相应的模块；

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

(4)client 通过mbox_send_message给controller发送数据的时候必须指定channel；

int mbox_send_message(struct mbox_chan *chan, void *mssg)

(5)client 在通过mbox_send_message给controller发送数据的时候必须指定channel,channel可以通过以下方式获得。

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的一个封装。

2 基本框架

目录：

drivers/mailbox

mailbox.c/mailbox.h/mailbox-test.c/-mailbox.c

3 关键数据结构

struct mbox_controller {

struct device *dev;                                      // 特定mailbox驱动probe时赋值 dev = &pdev->dev

const struct mbox_chan_ops *ops;                         // mailbox channel需要实现的功能函数

struct mbox_chan *chans;                                 // mailbox channel指针数组

int num_chans;                                           // mailbox channel个数

bool txdone_irq; // 通过中断来判断上次传输是否完成

bool txdone_poll;   // 通过poll机制来判断上次传输是否完成

unsigned txpoll_period;                                  // POLL 周期, 以ms计

struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,

const struct of_phandle_args *sp);     // 获取特定channel的回调函数

/* Internal to API */

struct hrtimer poll_hrt;

struct list_head node;

};

struct mbox_chan {

struct mbox_controller *mbox;                            // contronller指针

unsigned txdone_method;

struct mbox_client *cl;                                  // client指针

struct completion tx_complete;                           //

void *active_req;

unsigned msg_count, msg_free;

void *msg_data[MBOX_TX_QUEUE_LEN];

spinlock_t lock; /* Serialise access to the channel */

void *con_priv;

};

struct mbox_chan_ops {

int (*send_data)(struct mbox_chan *chan, void *data);         // 发送数据(需要last data sent)

int (*startup)(struct mbox_chan *chan);                       // 特定mailbox 启动

void (*shutdown)(struct mbox_chan *chan);                     // 特定mailbox 关闭

bool (*last_tx_done)(struct mbox_chan *chan);                 // 如果TXDONE_BY_POLL 该回调会被使用

bool (*peek_data)(struct mbox_chan *chan);                    // 检测是否有数据

};

struct mbox_client {

struct device *dev;                                           // client 设备

bool tx_block;                                                // block until last data is all transmitted

unsigned long tx_tout;                                        // max block period for timeout

bool knows_txdone;                                            // txdone 回调，如果controller已经有txdone，则该配置无效

void (*rx_callback)(struct mbox_client *cl, void *mssg);      // 收到数据

void (*tx_prepare)(struct mbox_client *cl, void *mssg); // 准备数据

void (*tx_done)(struct mbox_client *cl, void *mssg, int r);   // 检测txdone

};

4 函数接口

4.1 mailbox controller api

文件：kernel/include/linux/mailbox_controller.h

(1)注册、注销控制器

int mbox_controller_register(struct mbox_controller *mbox); /* can sleep */--------probe中调用

void mbox_controller_unregister(struct mbox_controller *mbox); /* can sleep */-------probe中调用

(2)(对外接口)将底层收到的数据回调给上层应用

void mbox_chan_received_data(struct mbox_chan *chan, void *data); /* atomic */

(3)通知上层当前数据已经发送完成

void mbox_chan_txdone(struct mbox_chan *chan, int r); /* atomic */

4.2 mailbox client api

文件：kernel/include/linux/mailbox_client.h

(1)发送数据前，申请通道

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);

(2)数据发送

int mbox_send_message(struct mbox_chan *chan, void *mssg);

void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */

(3)数据记录

bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */

(4)释放通道

void mbox_free_channel(struct mbox_chan *chan); /* may sleep */

5 Device Tree中的写法

kernel4.14/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt

Hisilicon Hi6220 Mailbox Driver

===============================

Hisilicon Hi6220 mailbox supports up to 32 channels. Each channel

is unidirectional with a maximum message size of 8 words. I/O is

performed using register access (there is no DMA) and the cell

raises an interrupt when messages are received.

Mailbox Device Node(Controller):(设备节点相关的设备树)

====================

Required properties:

--------------------

- compatible:        Shall be "hisilicon,hi6220-mbox"

- reg:            Contains the mailbox register address range (base

address and length); the first item is for IPC

registers, the second item is shared buffer for

slots.

- #mbox-cells:        Common mailbox binding property to identify the number

of cells required for the mailbox specifier. Must be 3.

phandle: Label name of mailbox controller

slot_id: Slot id used either for TX or RX

dst_irq: IRQ identifier index number which used by MCU

ack_irq: IRQ identifier index number with generating a

TX/RX interrupt to application processor,

mailbox driver uses it to acknowledge interrupt

- interrupts:        Contains the interrupt information for the mailbox

device. The format is dependent on which interrupt

controller the SoCs use.

Optional Properties:

--------------------

- hi6220,mbox-tx-noirq: Property of MCU firmware's feature, so mailbox driver

use this flag to ask MCU to enable "automatic idle

flag" mode or IRQ generated mode to acknowledge a TX

completion.

Example:

--------

mailbox: mailbox@f7510000 {

compatible = "hisilicon,hi6220-mbox";

reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */

<0x0 0x06dff800 0x0 0x0800>; /* Mailbox */

interrupt-parent = ;

interrupts = ;

#mbox-cells = <3>;

};

Mailbox client(client相关的设备树)

===============

Required properties:

--------------------

- compatible:        Many (See the client docs).

- mboxes:        Standard property to specify a Mailbox (See ./mailbox.txt)

Cells must match 'mbox-cells' (See Mailbox Device Node above).

Optional Properties:

--------------------

- mbox-names:        Name given to channels seen in the 'mboxes' property.

Example:

--------

stub_clock: stub_clock {

compatible = "hisilicon,hi6220-stub-clk";

hisilicon,hi6220-clk-sram = ;

#clock-cells = <1>;

mbox-names = "mbox-tx", "mbox-rx";

mboxes = , ;

};

Example：

kernel4.14/arch/arm64/boot/dts/hisilicon/hi6220.dtsi

mailbox: mailbox@f7510000 {

compatible = "hisilicon,hi6220-mbox";

reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */

<0x0 0x06dff800 0x0 0x0800>; /* Mailbox */

interrupt-parent = ;

interrupts = ;

#mbox-cells = <3>;

};

Example:

--------

stub_clock: stub_clock {

compatible = "hisilicon,hi6220-stub-clk";

hisilicon,hi6220-clk-sram = ;

#clock-cells = <1>;

mbox-names = "mbox-tx", "mbox-rx";

mboxes = , ;

};

6 原理详解

6.1 原理概述

(1)driver 通过mbox_controller_register 注册controller；

(2)client 通过mbox_request_channel调用driver->startup；

(3)client 通过mbox_send_message调用driver->send_data，并等待txdone；

(4)driver 收到remote的中断读取数据调用mbox_chan_received_data将数据放到 client->rx_buffer中；

6.1.1 mailbox driver流程

(1)配置controller属性:

(2)申请chan，配置chan个数

(3)配置of_xlate回调，获取chan

(4)配置chan_ops

(5)配置txdone判断方式

(6)通过mailbox_controller_register 注册controller；

6.1.2 mailbox client 流程

(1)通过mbox_request_channel_byname 根据"mbox-names"申请channel；

(2)创建mbox设备；

(3)通过mbox设备的write/read 函数访问controller；

其中，

write 通过调用mbox_send_message，add_to_rbuf拷贝msg到chan->msg_data[MAX = 20]，msg_submit读取msg_data[idx]，放到tx_prepare中，调用具体驱动的send message写寄存器；

read 通过irq驱动，irq读取寄存器得到消息，调用mailbox.c中的mbox_chan_received_data，再调用client的rx_callback将得到的数据放到client->rx_buffer中；

6.2 Mailbox Controller驱动

6.2.1 Mailbox Controller驱动初始化

6.2.1.1 mbox controller初始化函数

core_initcall(hi6220_mbox_init)

>>>platform_driver_register(&hi6220_mbox_driver);

module_exit(hi6220_mbox_exit);

>>>platform_driver_unregister(&hi6220_mbox_driver);

static struct platform_driver hi6220_mbox_driver = {

.driver = {

.name = "hi6220-mbox",

.owner = THIS_MODULE,

.of_match_table = hi6220_mbox_of_match,

},

.probe    = hi6220_mbox_probe,//mbox controller drivers 初始化函数

.remove    = hi6220_mbox_remove, //mbox controller drivers 逆初始化函数

};

static const struct of_device_id hi6220_mbox_of_match[] = {

{ .compatible = "hisilicon,hi6220-mbox", },

{},

};

6.2.1.2 调用probe/remove 函数

probe()函数主要用于初始化mbox controller.

hi6220_mbox_probe(struct platform_device *pdev)

>>>mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);//分配vendor设备结构体struct hi6220_mbox *mbox

>>>初始化struct hi6220_mbox *mbox中的相关成员变量

>>>mbox->mchan = devm_kzalloc(dev,mbox->chan_num * sizeof(*mbox->mchan), GFP_KERNEL);//为chan_num个struct hi6220_mbox_chan申请内存

>>>mbox->chan = devm_kzalloc(dev,mbox->chan_num * sizeof(*mbox->chan), GFP_KERNEL);//为chan_num个struct mbox_chan申请内存

>>>mbox->irq = platform_get_irq(pdev, 0);

>>>res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

mbox->ipc = devm_ioremap_resource(dev, res);

>>>    res = platform_get_resource(pdev, IORESOURCE_MEM, 1);

mbox->base = devm_ioremap_resource(dev, res);

>>>申请中断

err = devm_request_irq(dev, mbox->irq, hi6220_mbox_interrupt, 0,    dev_name(dev), mbox);//其中，hi6220_mbox_interrupt为中断mbox->irq对应的服务函数

>>>初始化controller

mbox->controller.dev = dev;

mbox->controller.chans = &mbox->chan[0];

mbox->controller.num_chans = mbox->chan_num;

mbox->controller.ops = &hi6220_mbox_ops;

mbox->controller.of_xlate = hi6220_mbox_xlate;

for (i = 0; i < mbox->chan_num; i++) {

mbox->chan[i].con_priv = &mbox->mchan[i];

mbox->irq_map_chan[i] = NULL;

mbox->mchan[i].parent = mbox;

mbox->mchan[i].slot   = i;

}

>>>mask and clear all interrupt vectors

writel(0x0,  ACK_INT_MSK_REG(mbox->ipc));

writel(~0x0, ACK_INT_CLR_REG(mbox->ipc));

>>>判断中断使用poll方式还是中断方式

/* use interrupt for tx's ack */

if (of_find_property(node, "hi6220,mbox-tx-noirq", NULL))

mbox->tx_irq_mode = false;

else

mbox->tx_irq_mode = true;

if (mbox->tx_irq_mode)

mbox->controller.txdone_irq = true;

else {

mbox->controller.txdone_poll = true;

mbox->controller.txpoll_period = 5;

}

>>>注册控制器

err = mbox_controller_register(&mbox->controller);

>>>保存mbox设备数据到pdev->dev->driver_data

platform_set_drvdata(pdev, mbox);

hi6220_mbox_remove(struct platform_device *pdev)

>>>struct hi6220_mbox *mbox = platform_get_drvdata(pdev);

>>>mbox_controller_unregister(&mbox->controller);

6.2.1.3 中断处理流程

probe函数中注册中断，driver 收到remote的中断，读取数据调用mbox_chan_received_data将数据放到 client->rx_buffer中

static irqreturn_t hi6220_mbox_interrupt(int irq, void *p)

>>>读取中断状态(哪个子中断置位？？？)

state = readl(ACK_INT_STAT_REG(mbox->ipc));

>>>    查询每个子中断的状态并进行响应

while (state) {

>>>查询中断状态中的最高置1的位

intr_bit = __ffs(state);//

state &= (state - 1);

chan = mbox->irq_map_chan[intr_bit];//每个中断位对应一个中断通道

if (!chan) {

dev_warn(mbox->dev, "%s: unexpected irq vector %d\n",

__func__, intr_bit);

continue;

}

mchan = chan->con_priv;         //通道私有数据

if (mchan->dir == MBOX_TX)      //若该通道(中断)为发送方向

mbox_chan_txdone(chan, 0);

else {                          //若该通道(中断)为接受方向

for (i = 0; i < MBOX_MSG_LEN; i++)

msg[i] = readl(mbox->base +MBOX_DATA_REG(mchan->slot) + i * 4);//读取数据

mbox_chan_received_data(chan, (void *)msg);    //将数据交给数据接受函数进行处理

}

/* clear IRQ source */清中断

writel(BIT(mchan->ack_irq), ACK_INT_CLR_REG(mbox->ipc));

mbox_set_state(mbox, mchan->slot, MBOX_STATE_IDLE);

}

6.2.2 数据接收流程

数据接收是以中断的方式进行的。

hi6220_mbox_interrupt()

>>>for (i = 0; i < MBOX_MSG_LEN; i++)

msg[i] = readl(mbox->base +MBOX_DATA_REG(mchan->slot) + i * 4);//读取数据

>>>mbox_chan_received_data(chan, (void *)msg);    //讲数据交给数据接受函数进行处理

>>>chan->cl->rx_callback(chan->cl, mssg); //上层client回调

6.2.3 数据发送流程

6.2.3.1 数据发送分为三种方式

中断方式，polling方式，ACK方式

#define TXDONE_BY_IRQ    BIT(0) /* controller has remote RTR irq */

#define TXDONE_BY_POLL    BIT(1) /* controller can read status of last TX */

#define TXDONE_BY_ACK    BIT(2) /* S/W ACK recevied by Client ticks the TX */

6.2.3.2 数据发送的基本流程

1 获取mailbox的channel

1)申请通道时，client对象指定了自己的需求和能力；

2)在原子上下文中不能调用；

3)通道在一个client占用之后，没有释放之前，不能被其它client使用；

4)分配完成之后，任何此通道上接受的数据包将通过rx_callback传递到客户端

5)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 */

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);

struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)

函数功能：通过dts中配置的channel index申请通道

>>>of_parse_phandle_with_args(dev->of_node, "mboxes", "#mbox-cells", index, &spec)

>>>根据dts中配置的channel index获得mbox_chan

list_for_each_entry(mbox, &mbox_cons, node)

chan = mbox->of_xlate(mbox, &spec);

>>>初始化mbox

chan->msg_free = 0;

chan->msg_count = 0;

chan->active_req = NULL;

chan->cl = cl;

init_completion(&chan->tx_complete);

>>>启动通道

ret = chan->mbox->ops->startup(chan);

struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,const char *name);

函数功能：通过channel name 申请通道，调用mbox_request_channel()函数来实现

2 使用mbox_send_message给controller发送数据

函数功能：在client提交数据到controller进而发送到目标处理器的过程中。

若client设置为tx_block，此函数调用只有在远程已经完成数据接受或tx_out(超时)才能返回；

若client设置为非block模式下，client的每个请求将被此API进行缓存，并返回一个非负数；

若client请求没有进入queue,将返回一个负数。

无论失败，还是成功，API将调用tx_done；

int mbox_send_message(struct mbox_chan *chan, void *mssg)

>>>    t = add_to_rbuf(chan, mssg);    //将要发送的msg发暂存到对应通道的rbuf中

>>>msg_submit(chan);

>>>data = chan->msg_data[idx];

>>>chan->cl->tx_prepare(chan->cl, data);   //发到缓存

>>>err = chan->mbox->ops->send_data(chan, data);  //发送数据  hi6220_mbox_send_data,

>>>mbox_set_state(mbox, slot, MBOX_STATE_TX);

>>>if (mbox->tx_irq_mode)

mbox_set_mode(mbox, slot, MBOX_ACK_IRQ);

>>>发送数据

for (i = 0; i < MBOX_MSG_LEN; i++)

writel(buf[i], mbox->base + MBOX_DATA_REG(slot) + i * 4);

>>>/* trigger remote request */

writel(BIT(mchan->dst_irq), DST_INT_RAW_REG(mbox->ipc));

等待中断。。。。。。。。。。

------------------------------------------------------

在中断服务函数中

发送完成中断到来----------->

>>>hi6220_mbox_interrupt

>>>mbox_chan_txdone(chan, 0);

>>>tx_tick(chan, r);

>>>msg_submit(chan);

>>>chan->cl->tx_done(chan->cl, mssg, r);

------------------------------------------------------

>>>若为polling方式下，启定时器

hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);

>>>若为block形式的发送

>>>设置超时时间

wait = msecs_to_jiffies(3600000);//永不超时

wait = msecs_to_jiffies(chan->cl->tx_tout);

>>>阻塞等待超时或完成

ret = wait_for_completion_timeout(&chan->tx_complete, wait);

>>>若超时时间到

tx_tick(chan, t);

>>>chan->cl->tx_done(chan->cl, mssg, r);

>>>complete(&chan->tx_complete);

6.3 Mailbox Client驱动

以mailbox-test为例说明。

struct mbox_test_device {

struct device        *dev;

void __iomem        *tx_mmio;

void __iomem        *rx_mmio;

struct mbox_chan    *tx_channel;

struct mbox_chan    *rx_channel;

char            *rx_buffer;

char            *signal;

char            *message;

spinlock_t        lock;

wait_queue_head_t    waitq;

struct fasync_struct    *async_queue;

};

6.3.1 Client 设备树相关的配置

Controller

----------

Required properties:

- compatible : Should be "st,stih407-mailbox"

- reg : Offset and length of the device's register set

- mbox-name : Name of the mailbox

- #mbox-cells: : Must be 2

phandle : Label name of controller

instance : Instance number

channel : Channel number

Optional properties

- interrupts : Contains the IRQ line for a Rx mailbox

Example:

mailbox0: mailbox@0 {

compatible = "st,stih407-mailbox";

reg = <0x08f00000 0x1000>;

interrupts = ;

#mbox-cells = <2>;

mbox-name = "a9";

};

Client

------

Required properties:

- compatible : Many (See the client docs)

- reg : Shared (between Application and Remote) memory address

- mboxes : Standard property to specify a Mailbox (See ./mailbox.txt)

Cells must match 'mbox-cells' (See Controller docs above)

Optional properties

- mbox-names : Name given to channels seen in the 'mboxes' property.

Example:

mailbox_test {

compatible = "mailbox-test";

reg = <0x[shared_memory_address], [shared_memory_size]>;

mboxes = , ;

mbox-names = "tx", "rx";

};

6.3.2 Client初始化

static struct platform_driver mbox_test_driver = {

.driver = {

.name = "mailbox_test",

.of_match_table = mbox_test_match,

},

.probe = mbox_test_probe,

.remove = mbox_test_remove,

};

module_platform_driver(mbox_test_driver);

static int mbox_test_probe(struct platform_device *pdev)

>>>tdev = devm_kzalloc(&pdev->dev, sizeof(*tdev), GFP_KERNEL);

>>>res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

>>>size = resource_size(res);

>>>tdev->tx_mmio = devm_ioremap_resource(&pdev->dev, res);

>>>申请通道

tdev->tx_channel = mbox_test_request_channel(pdev, "tx");

tdev->rx_channel = mbox_test_request_channel(pdev, "rx");

>>> client = devm_kzalloc(&pdev->dev, sizeof(*client), GFP_KERNEL);

>>> client->dev= &pdev->dev;

>>> client->rx_callback= mbox_test_receive_message;

>>> client->tx_prepare= mbox_test_prepare_message;

>>> client->tx_done= mbox_test_message_sent;

>>> client->tx_block= true;

>>> client->knows_txdone= false;

>>> client->tx_tout= 500;

>>> channel = mbox_request_channel_byname(client, name); //调用API申请通道

>>>platform_set_drvdata(pdev, tdev);

>>>spin_lock_init(&tdev->lock);

>>>tdev->rx_buffer = devm_kzalloc(&pdev->dev,

MBOX_MAX_MSG_LEN, GFP_KERNEL);

>>>ret = mbox_test_add_debugfs(pdev, tdev);

>>>init_waitqueue_head(&tdev->waitq);

static int mbox_test_remove(struct platform_device *pdev)

>>> debugfs_remove_recursive(root_debugfs_dir);

>>> mbox_free_channel(tdev->tx_channel);

>>> mbox_free_channel(tdev->rx_channel);

6.3.3 Client数据收发

数据接收(回调函数)

static void mbox_test_receive_message(struct mbox_client *client, void *message)

spin_lock_irqsave(&tdev->lock, flags);

if (tdev->rx_mmio) {

memcpy_fromio(tdev->rx_buffer, tdev->rx_mmio, MBOX_MAX_MSG_LEN);

} else if (message) {

memcpy(tdev->rx_buffer, message, MBOX_MAX_MSG_LEN);

}

mbox_data_ready = true;

spin_unlock_irqrestore(&tdev->lock, flags);

wake_up_interruptible(&tdev->waitq);

kill_fasync(&tdev->async_queue, SIGIO, POLL_IN);

数据发送

static void mbox_test_prepare_message(struct mbox_client *client, void *message)

{

struct mbox_test_device *tdev = dev_get_drvdata(client->dev);

if (tdev->tx_mmio) {

if (tdev->signal)

memcpy_toio(tdev->tx_mmio, tdev->message, MBOX_MAX_MSG_LEN);

else

memcpy_toio(tdev->tx_mmio, message, MBOX_MAX_MSG_LEN);

}

}

static void mbox_test_message_sent(struct mbox_client *client,

void *message, int r)

{

if (r)

dev_warn(client->dev,

"Client: Message could not be sent: %d\n", r);

else

dev_info(client->dev,

"Client: Message sent\n");

}

————————————————

版权声明：本文为CSDN博主「huofengfeihu」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。

原文链接：https://blog.csdn.net/u010961173/article/details/96422441