Freescale mma845x三轴加速度传感器驱动分析

最近刚看完freescale mma8451的驱动，并且一直了驱动，自己也没怎么改代码，不过读了一下代码，还是有点体会的，下面我就来分析一下。

首先看下代码结构，有兴趣的可以从一下方式获得代码，[e-mail]:zhangjie201412/WorkSpace.git ，最好是先发mail给我，

jay@jay:~/mygit$ tree
.
└── kernel
├── arch
│ └── arm
│ └── mach-mx5
│ └── mx53_smd.c
├── drivers
│ └── hwmon
│ └── mma845x
│ ├── Makefile
│ ├── mma845x.c
│ ├── mma845x.h
│ ├── mma_char.c
│ ├── mma_core.c
│ ├── mma_input.c
│ ├── mma_regs.h
│ ├── mma_sysfs.c
│ └── mma_sysfs.h
└── include
└── linux
└── mma845x.h

其中一个头文件，然后是一个驱动包，里面内容蛮丰富的，还有就是要在板级文件里面注册platform的device端，我这里是基于iMX53的Android BSP

首先咱还是来找源头吧，找啊找，看名字就知道我们先要分析这个mma_core.c文件

static int __init init_mma845x(void)
{
    /*
     * register driver 
     */
    printk(KERN_INFO "add mma i2c driver\n");
    return i2c_add_driver(&i2c_mma845x_driver);
}

/*!
* This function implements "exit" routine for driver
*/
static void __exit exit_mma845x(void)
{
    printk(KERN_INFO "del mma i2c driver.\n");
#ifdef CONFIG_EARLYSUSPEND
    // Register early_suspend and late_wakeup handlers
    unregister_early_suspend(&mma845x_early_suspend_desc);
#endif
    return i2c_del_driver(&i2c_mma845x_driver);
}

module_init(init_mma845x);
module_exit(exit_mma845x);

这个初始化和卸载模块就不多说了，注册了i2c类型的驱动，接着去platform文件中找注册的device端，mx53_smd.c

//+++add head file for g-sensor
#include <linux/mma845x.h>

//++++add for mma driver
static struct mxc_mma845x_platform_data mma845x_data = {
	.gpio_pin_get = NULL,
	.gpio_pin_put = NULL,
	.int1 = gpio_to_irq(MX53_SMD_ACCL_INT1_IN), // ACCL_INT1 is gpio for MMA845X INT1

	.int2 = gpio_to_irq(MX53_SMD_ACCL_INT2_IN), // ACCL_INT2 is gpio for MMA845X INT2
};
//-----add by Jay end

static struct i2c_board_info mxc_i2c0_board_info[] __initdata = {
	{
	.type = "mma845x",
	.addr = 0x1C,
//	.irq = gpio_to_irq(MX53_SMD_ACCL_INT1_IN),	//+++++add by Jay for g-sensor interrupt mode
	.platform_data = (void *)&mma845x_data,	//+++add by Jay
	 },
	{
	.type = "ov5642",
	.addr = 0x3C,
	.platform_data = (void *)&camera_data,
	 },
	{
	.type = "mma7660",
	.addr = 0x4C,
	 },
};

这里，填充了mma845x驱动的一些platform_data

然后是注册，

	i2c_register_board_info(0, mxc_i2c0_board_info,
				ARRAY_SIZE(mxc_i2c0_board_info));

这个函数会把i2c0上的所有驱动都挂到platform driver的device上去，进行匹配，这里我要提示的一点是，这里的2根GPIO 中断引脚，我们要设置为input

	//+++++add by Jay for g-sensor interrupt mode to get data
	gpio_request(MX53_SMD_ACCL_INT1_IN, "gsensor-irq");
	msleep(5);
	gpio_direction_input(MX53_SMD_ACCL_INT1_IN);
	//-----end add

接下来分析mma_core.c中的probe函数，这里是最终要的一个函数了

/*!
* This function implements probe routine for driver
* client     : pointer to i2c client
* id         : i2c device id
* return 0         : Success
* return -ENOMEM   : Memory allocation for pDev failed
* return -ENODEV   : Platform data not found
*/
static int mma845x_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
    int ret = 0,
    i = 0;
    struct ChipInfo_t *pChip = NULL;
    struct mxc_mma_device_t *pDev = NULL;
    int             mask = 0;
   
    plat_data =
	(struct mxc_mma845x_platform_data *) client->dev.platform_data;
    if (plat_data == NULL) {
	dev_err(&client->dev, "lack of platform data!\n");
	return -ENODEV;
    }

    pDev = kzalloc(sizeof(struct mxc_mma_device_t), GFP_KERNEL);
    if (!pDev) {
	pDev = NULL;
	return -ENOMEM;
    }

     printk(KERN_INFO "\r\nProbing Module: %s %s\r\n", MODULE_NAME, DRIVER_VERSION);
     printk(KERN_INFO "Freescale Android 2.3 Release: %s\r\n", ANDROID_RELEASE); 
     printk(KERN_INFO "Build Date: %s [%s]\r\n", __DATE__, __TIME__);
    
    i2c_set_clientdata(client, pDev);

    /*
     * bind the right device to the driver 
     */
    ret = IdentifyChipset(client);
    if (ret < 0) {
	 printk(KERN_INFO "%s:: Unable to identify device.\r\n", __func__);
	return -EIO;
    }

    /*
     * Associate chip layer 
     */
    for (i = 0; i < sizeof(ChipTable) / sizeof(ChipTable[0]); i++) {
	if (ChipTable[i]->ChipId == ret) {
	    pChip = ChipTable[i];
	    pChip->ChipId = ret;
	    pChip->client = client;
	    pChip->ChipType = ChipType;
	    break;
	}
    }

    if (i >= (sizeof(ChipTable) / sizeof(ChipTable[0]))) {
	 printk(KERN_INFO "Chipset not supported by MMA driver\r\n");
	return -ENOMEM;
    }

    gpChip = pChip;
    gpDev = pDev;
    SetDefaultVal(pChip);

    /*
     * Inialize default event codes 
     */
    pDev->fm_event_type = 0x25;
    pDev->ornt_event_type = 0x26;
    pDev->trans_event_type = 0x27;
    pDev->event_type_single = 0x28;
    pDev->event_type_double = 0x29;

    pDev->aflag = 1;
    /*
     * Initialize chipset 
     */
    pChip->Init(pChip);

    pDev->pChip = pChip;
    pDev->version = 1;

    /*
     * configure gpio as input for interrupt monitor 
     */

    if(plat_data->gpio_pin_get)
	    plat_data->gpio_pin_get();

    /*
     * Register character device 
     */
    pDev->major = register_chrdev(0, "mma", &mma_fops);
    if (ret < 0) {
	 printk(KERN_INFO "%s:: Unable to register device\r\n", __func__);
	goto error_disable_power;
    }

    strcpy(pDev->devname, "mma");
    printk(KERN_INFO "%s:: Registered char dev \"%s\" @ %d\r\n", __func__,
	pDev->devname, pDev->major);

    /*
     * Initialize input layer 
     */
    InitializeInputInterface(pDev);

    /*
     * Create sysfs entries 
     */
    InitializeSysfs( (struct i2c_client *)client);

    /*
     * Initialize semaphore for interrupt
     */
    sema_init(&chip_ready, 0);

    setup_timer(&stall_timer, stall_timer_fn, 0);
    hIstThread = kthread_run(IntServiceThread, pDev, "mxc845x_ist");
    if (IS_ERR(hIstThread)) {
	 printk(KERN_INFO "Error creating mxc845x ist.\n");
	goto error_free_irq1;
    }
    if (plat_data->int1 > 0)  {   
	    set_irq_type(plat_data->int1, IRQF_TRIGGER_FALLING);

	    ret = request_irq(plat_data->int1, mma845x_interrupt,
			      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);

	    if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
			plat_data->int1, ret);
		goto error_disable_power;
	    }
    }
    else {
		gpChip->DisableInt(INT_EN_FIFO | INT_EN_DRDY);
		poll_mode = 1;
	}
    if (plat_data->int2 > 0){
    	 printk(KERN_INFO "%s:: Configuring interrupt IRQ [%d]\r\n", __func__,
	   plat_data->int2);

   	 set_irq_type(plat_data->int2, IRQF_TRIGGER_FALLING);
   	 ret = request_irq(plat_data->int2, mma845x_interrupt,
		      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);
     if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
		plat_data->int2, ret);
		goto error_free_irq1;
     }
   }
#ifdef CONFIG_EARLYSUSPEND
    register_early_suspend(&mma845x_early_suspend_desc);
#endif

注释也写的蛮清楚的但是咱还是一起来看一下

    plat_data =
	(struct mxc_mma845x_platform_data *) client->dev.platform_data;
    if (plat_data == NULL) {
	dev_err(&client->dev, "lack of platform data!\n");
	return -ENODEV;
    }

这里是由probe函数传进来的client参数来得到platform_data，就是我们在板级文件中填充的那些个结构体，我觉得Linux设计的这个platform架构的驱动很好，他可以很好的把驱动和设备隔离开来，虽然有的时候还是会联系到一起，但是对于可移植性更强了，因为，驱动只是对设备的统一管理，而platform device端只需要配置cpu的gpio跟deivce的连接情况，还有一些soc中继承的功能的配置以及注册。

    pDev = kzalloc(sizeof(struct mxc_mma_device_t), GFP_KERNEL);
    if (!pDev) {
	pDev = NULL;
	return -ENOMEM;
    }

     printk(KERN_INFO "\r\nProbing Module: %s %s\r\n", MODULE_NAME, DRIVER_VERSION);
     printk(KERN_INFO "Freescale Android 2.3 Release: %s\r\n", ANDROID_RELEASE); 
     printk(KERN_INFO "Build Date: %s [%s]\r\n", __DATE__, __TIME__);

接着这里是给我们驱动中定义的mxc_mma_device_t结构体分配内存，然后是一些kernel info的打印没什么好说了。

还是先来看一下这个结构体吧，

/*sensor platform data structure for mma8451/mma8452/mma8453*/
struct mxc_mma845x_platform_data {
	void (*gpio_pin_get) (void);
	void (*gpio_pin_put) (void);
	int int1;
	int int2;
};

这个结构体比较简单，定义了2个中断号，还有中断GPIO的get和put，我们这边对这2个函数没有实现，我猜想get函数是对中断GPIO的配置，put是对中断GPIO的free，拙见而已，

   i2c_set_clientdata(client, pDev);

    /*
     * bind the right device to the driver 
     */
    ret = IdentifyChipset(client);
    if (ret < 0) {
	 printk(KERN_INFO "%s:: Unable to identify device.\r\n", __func__);
	return -EIO;
    }

    /*
     * Associate chip layer 
     */
    for (i = 0; i < sizeof(ChipTable) / sizeof(ChipTable[0]); i++) {
	if (ChipTable[i]->ChipId == ret) {
	    pChip = ChipTable[i];
	    pChip->ChipId = ret;
	    pChip->client = client;
	    pChip->ChipType = ChipType;
	    break;
	}
    }

    if (i >= (sizeof(ChipTable) / sizeof(ChipTable[0]))) {
	 printk(KERN_INFO "Chipset not supported by MMA driver\r\n");
	return -ENOMEM;
    }

    gpChip = pChip;
    gpDev = pDev;
    SetDefaultVal(pChip);

    /*
     * Inialize default event codes 
     */
    pDev->fm_event_type = 0x25;
    pDev->ornt_event_type = 0x26;
    pDev->trans_event_type = 0x27;
    pDev->event_type_single = 0x28;
    pDev->event_type_double = 0x29;

    pDev->aflag = 1;
    /*
     * Initialize chipset 
     */
    pChip->Init(pChip);

    pDev->pChip = pChip;
    pDev->version = 1;

    /*
     * configure gpio as input for interrupt monitor 
     */

    if(plat_data->gpio_pin_get)
	    plat_data->gpio_pin_get();

    /*
     * Register character device 
     */

这里首先是对mma_845x器件身份的识别，来看下IdentifyChipset函数

/*!
* This function Identify the chip connected on bus and associate client driver for the chipset 
* client   : i2c_client pointer for i2c bus attached to device
* return chip_id : Chip id of identified device
* return -1      : Device not identified
*/
static int IdentifyChipset(struct i2c_client *client)
{
    int             retVal = 0;
    int             ChipIdentified = 0;

    retVal = i2c_smbus_read_byte_data(client, REG(WHO_AM_I));
    switch (retVal) {
    case ID_MMA8451:
	{
	    printk("%s:: Found MMA8451 chipset with chip ID 0x%02x\r\n",
		   __func__, retVal);
	    ChipIdentified = 1;
	}
	break;

    case ID_MMA8452:
	{
	    printk("%s:: Found MMA8452 chipset with chip ID 0x%02x\r\n",
		   __func__, retVal);
	    ChipIdentified = 1;
	}
	break;

    case ID_MMA8453:
	{
	    printk("%s:: Found MMA8453 chipset with chip ID 0x%02x\r\n",
		   __func__, retVal);
	    ChipIdentified = 1;
	}
	break;

    default:
	{
	    printk("%s:: Not a valid MMA845X chipset. Chip ID 0x%02x\r\n",
		   __func__, retVal);
	    ChipIdentified = 0;
	}
	break;

读i2c bus上面mma传感器的WHO_AM_I 寄存器，来判断连上的是哪个device

    /*
     * Associate chip layer 
     */
    for (i = 0; i < sizeof(ChipTable) / sizeof(ChipTable[0]); i++) {
	if (ChipTable[i]->ChipId == ret) {
	    pChip = ChipTable[i];
	    pChip->ChipId = ret;
	    pChip->client = client;
	    pChip->ChipType = ChipType;
	    break;
	}
    }

    if (i >= (sizeof(ChipTable) / sizeof(ChipTable[0]))) {
	 printk(KERN_INFO "Chipset not supported by MMA driver\r\n");
	return -ENOMEM;
    }

    gpChip = pChip;
    gpDev = pDev;
    SetDefaultVal(pChip);

这里首先是对芯片层的一些赋值，找到这里我们注册的是哪款芯片，然后把i2c client，chip id， chiptype等信息赋值给这里的局部变量，然后再把局部变量赋值给全局的几个指针，然后再试对芯片寄存器设置一些默认值。

    /*
     * Inialize default event codes 
     */
    pDev->fm_event_type = 0x25;
    pDev->ornt_event_type = 0x26;
    pDev->trans_event_type = 0x27;
    pDev->event_type_single = 0x28;
    pDev->event_type_double = 0x29;

    pDev->aflag = 1;
    /*
     * Initialize chipset 
     */
    pChip->Init(pChip);

    pDev->pChip = pChip;
    pDev->version = 1;

然后是初始化芯片的事件类型，这里这块芯片分很多事件类型，有撞击事件，横竖切换事件等，接下来如果pChip结构体中Init成员函数非空的话就执行这个函数。

    /*
     * Register character device 
     */
    pDev->major = register_chrdev(0, "mma", &mma_fops);
    if (ret < 0) {
	 printk(KERN_INFO "%s:: Unable to register device\r\n", __func__);
	goto error_disable_power;
    }

    strcpy(pDev->devname, "mma");
    printk(KERN_INFO "%s:: Registered char dev \"%s\" @ %d\r\n", __func__,
	pDev->devname, pDev->major);

接下来注册了一个字符类型的驱动，咱来看看这个驱动是干啥用的，最主要的还是看mma_fops这个文件操作结构体中实现了哪些个东西，mma_char.c

/* 
 * This structure is the file operations structure, which specifies what
 * callbacks functions the kernel should call when a user mode process
 * attempts to perform these operations on the device.
 */
const struct file_operations mma_fops = {
	.owner	 = THIS_MODULE,
	.open	 = mma_open,
	.ioctl 	 = mma_ioctl,
	.release = mma_release,
	.read 	 = mma_read,
};

这里有打开关闭，读，还有ioctl功能，

/*!
* Open call for accelerometer char driver. 
* inode : Pointer to the node to be opened.
* file  : Pointer to file structure.
* return 0    : After successful opening.  
*/

static int mma_open(struct inode * inode, struct file * file)
{
	pContext_t p = file->private_data;

	if (!p) {
		p = kmalloc(sizeof(*p), GFP_KERNEL);
		if (!p)
			return -ENOMEM;

		p->threshold = 5;
		p->read_pos = 0;
		sema_init(&p->sem, 1);
		file->private_data = p;
	}
	return 0;	
}

首先是open函数，这里还要先看下pContext_t这个结构体

typedef struct
{
	struct semaphore sem;
	int threshold;
	int read_pos;
}Context_t, *pContext_t;

里面有3个成员变量，乍看之下还不清楚是用来干嘛的，先不管，接着往下看就明白了，回到open函数中，首先把文件结构体中的数据给这个结构体，然后判断，这里的意思应该是如果open函数被打开了一次那么就会执行if中的代码，如果已经被打开了，那么就直接返回零，if语句中也就是多结构体的初始化，还有初始化了一个信号量，然后把p指针传给file->private，代表已经被打开了，非空。

/*!
* Release call for accelerometer char driver. 
* inode : Pointer to the node to be opened.
* file  : Pointer to file structure.
* return 0    : After successful release of resources.  
*/

static int mma_release(struct inode *inode, struct file *file)
{
	pContext_t p = file->private_data;

	if (p) 
	{
		mutex_destroy(&p->lock);
		kfree(p);
		p = NULL;
	}

	return 0;
}

release中的代码就不多说了，跟open函数正好相反。

然后是比较重要的ioctl和read function

/*!
* read call for accelerometer char driver. 
* inode    : Pointer to the node to be opened.
* file     : Pointer to file structure.
* command  : contains command for register.
* arg      : contains data required to apply settings specified in cmd.
* return  0      : For successful	 
*/

static int mma_ioctl(struct inode *inode, struct file *filp,
		  unsigned int command, unsigned long arg)
{
	pContext_t dev = filp->private_data;
	u32 threshold = 0;
	
	switch(command)
	{
		case MMA_GET_THRESHOLD:
			{

				if (copy_to_user(&arg, &(dev->threshold), sizeof(u32)))
			       	{
					printk("ioctl, copy to user failed\n");
					return -EFAULT;
				}
			}
			break;

		case MMA_GET_THRESHOLD_VALUE:
			{

				return dev->threshold;
			}
			break;

		case MMA_SET_THRESHOLD:
			{
				if (copy_from_user(&threshold, &arg, sizeof(u32)))
			       	{
					return -EFAULT;
				}
				if(threshold <= 0)
				{
					return -EINVAL;
				}
				
				dev->threshold = threshold;
			}
			break;

		case MMA_SET_THRESHOLD_VALUE:
			{
				threshold = arg;
				if(threshold <= 0)
				{
					printk("Invalid value [0x%x]\r\n", threshold);
					return -EINVAL;
				}
				dev->threshold = threshold;
			}
			break;

		case MMA_GET_ACCLEROMETER_FLAG:
			{

				return GetAcclerometerFlag();
			}
			break;

		case MMA_SET_ACCLEROMETER_FLAG:
			{
				int AcclFlag = arg;

				return SetAcclerometerFlag(AcclFlag);
			}
			break;

		default:
			{
				printk("%s:: Invalid IOCTL [0x%x]\r\n", __func__, command);
			}
	}
	return 0;
}

这个ioctl函数很简单，通过switch case语句，把用户传进去的参数分类，然后做出不同的动作，其中有对threshold的设置，读取，对acclerometer_flag的设置和获取等动作。

/*!
* read call for pressure char driver. 
* file  : Pointer to file structure.
* buf 	 : Pointer to user buffer in which data will be read.
* size  : Size of data be read.
* ppos  : Pointer to Offset in the file.
* return  1. no of bytes read - For successful read \
   	     2. ENOMEM - file private data pointer is NULL	 
*/

static ssize_t mma_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	int retval = 0;
	unsigned short nr = 0;
	pContext_t dev = file->private_data;
	int bytestocopy = 0;
	unsigned long bytescopied = 0;
	char __user *buff = buf;

	unsigned short hdr = 0xffff;

	if (!dev) 
	{
		return -ENOMEM;
	}

	/* Acquire semaphore to manage re-entrancy */
	if (down_interruptible(&dev->sem))
		return -ERESTARTSYS;


	/* Loop till data available has crossed the watermark */
	nr = GetAvailableData(dev->read_pos);
	while (nr < dev->threshold ) 
	{ 
		/* Wait on accelerometer queue (AcclQ) till condition GetAvailableData(dev->read_pos) >= dev->threshold gets satisfied */
		if (wait_event_interruptible(AcclDataQ, 
					(GetAvailableData(dev->read_pos) >= dev->threshold)))
			return -ERESTARTSYS;
		nr = GetAvailableData(dev->read_pos);
	}

	bytescopied = copy_to_user(buff, &hdr, sizeof(unsigned short));
	retval += sizeof(unsigned short);
	buff += sizeof(unsigned short);
	bytescopied = copy_to_user(buff, &nr, sizeof(unsigned short));

	retval += sizeof(unsigned short);
	buff += sizeof(unsigned short);

	/* Loop here to copy bytes to user buffer */
	while(nr)
	{
		if(dev->read_pos + nr >= ACCL_FIFO_SIZE)
		{
			bytestocopy = ACCL_FIFO_SIZE - dev->read_pos ;
		}
		else
		{
			bytestocopy = nr;
		}

		/* Copy the required records to user buffer */
		bytescopied = copy_to_user(buff, &AcclDataFifo[dev->read_pos], bytestocopy * sizeof(AcclData_t));

		retval += bytestocopy * sizeof(AcclData_t);
		buff += bytestocopy * sizeof(AcclData_t);
		
		nr -= bytestocopy;

		/* Increment the read_pos */
		dev->read_pos += bytestocopy;
		if(dev->read_pos >= ACCL_FIFO_SIZE)
			dev->read_pos -= ACCL_FIFO_SIZE;
	}
	/* release the lock */
	up(&dev->sem); 
	/* Return the number of bytes written to buffer */
	return retval;
}

这个函数看上去很复杂，其实就做了一件事情，调用copy_to_user把数据传到用户空间，其实这里我很不明白这个字符驱动到底跟我们的mma器件有什么关系，因为这里read函数中我没有看到一点关于i2cread 的内容，所以我觉得，这里这个字符驱动是多余的，不过这里对等待队列的读操作有待学习。

我们也可以自己再这里加上对I2C的读操作来把这里的read函数挂到用户空间，我想这里的ioctl函数应该是来设置threshold的，应该是用在HAL层中来被设置的。

而这里的read函数也可以当做poll模式下来读取xyz的数据，大家可以看到在read中有作比较，当读回来的数据大于threshold时才把数据copy到用户空间。

OK，这个字符驱动暂时介绍到这边，下面我们接着看mma_core.c中的probe函数

    /*
     * Initialize input layer 
     */
    InitializeInputInterface(pDev);

    /*
     * Create sysfs entries 
     */
    InitializeSysfs( (struct i2c_client *)client);

    /*
     * Initialize semaphore for interrupt
     */
    sema_init(&chip_ready, 0);

    setup_timer(&stall_timer, stall_timer_fn, 0);
    hIstThread = kthread_run(IntServiceThread, pDev, "mxc845x_ist");
    if (IS_ERR(hIstThread)) {
	 printk(KERN_INFO "Error creating mxc845x ist.\n");
	goto error_free_irq1;
    }
    if (plat_data->int1 > 0)  {   
	    set_irq_type(plat_data->int1, IRQF_TRIGGER_FALLING);

	    ret = request_irq(plat_data->int1, mma845x_interrupt,
			      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);

	    if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
			plat_data->int1, ret);
		goto error_disable_power;
	    }
    }
    else {
		gpChip->DisableInt(INT_EN_FIFO | INT_EN_DRDY);
		poll_mode = 1;
	}
    if (plat_data->int2 > 0){
    	 printk(KERN_INFO "%s:: Configuring interrupt IRQ [%d]\r\n", __func__,
	   plat_data->int2);

   	 set_irq_type(plat_data->int2, IRQF_TRIGGER_FALLING);
   	 ret = request_irq(plat_data->int2, mma845x_interrupt,
		      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);
     if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
		plat_data->int2, ret);
		goto error_free_irq1;
     }
   }

这里是一些列的初始化，input sybsystem、文件系统、信号量、定时器、线程的初始化，先看输入子系统初始化过程

int InitializeInputInterface(struct mxc_mma_device_t *pDev)
{
	int RetVal = 0;
	int i = 0;

	if(pDev == NULL)
	{
		printk("%s: pDev => NULL pointer\r\n", __func__);
		return -EPERM;
	}

	pDev->inp1 = input_allocate_device();

	if (!pDev->inp1)
       	{
		RetVal = -ENOMEM;
		printk(KERN_ERR
		       "%s: Failed to allocate input device-1\n", __func__);
		return RetVal;
	}

	set_bit(EV_ABS, pDev->inp1->evbit);						// Accelerometer readings

	/* yaw */
	input_set_abs_params(pDev->inp1, ABS_RX, 0, 360, 0, 0);
	/* pitch */
	input_set_abs_params(pDev->inp1, ABS_RY, -180, 180, 0, 0);
	/* roll */
	input_set_abs_params(pDev->inp1, ABS_RZ, -90, 90, 0, 0);

	/* x-axis acceleration */
	input_set_abs_params(pDev->inp1, ABS_X, -32768, 32767, 0, 0);
	/* y-axis acceleration */
	input_set_abs_params(pDev->inp1, ABS_Y, -32768, 32767, 0, 0);
	/* z-axis acceleration */
	input_set_abs_params(pDev->inp1, ABS_Z, -32768, 32767, 0, 0);

	pDev->inp1->name = "mma8451";

	RetVal = input_register_device(pDev->inp1);

	if (RetVal) 
	{
		printk(KERN_ERR "%s: Unable to register input device: %s\n",__func__, pDev->inp1->name);
		return RetVal;
	}
	
	/* Register input device 2 */
	pDev->inp2 = input_allocate_device();

	if (!pDev->inp2)
       	{
		RetVal = -ENOMEM;
		printk(KERN_ERR "%s: Failed to allocate input device-2\n", __func__);
		return RetVal;
	}

	/* Initialize all event codes as this is a configurable param and may change runtime from user space */
	for(i = 0x20; i < 0x40; i++)
		input_set_abs_params(pDev->inp2, i, 0, 255, 0, 0);

	pDev->inp2->mscbit[0] = BIT_MASK(MSC_RAW) | BIT_MASK(MSC_SCAN);


	pDev->inp2->name = "Accl1";

	set_bit(EV_ABS, pDev->inp2->evbit);
	set_bit(EV_KEY, pDev->inp2->evbit);
	set_bit(EV_MSC, pDev->inp2->evbit);

	RetVal = input_register_device(pDev->inp2);

	bitmap_fill(pDev->inp2->keybit, KEY_MAX);

	if (RetVal) 
	{
		printk(KERN_ERR "%s: Unable to register input device: %s\n", __func__, pDev->inp2->name);
		return RetVal;
	}
	return RetVal;	
}

分别调用input_allocate_device和input_register_device函数来注册input 驱动，然后就是设置input 驱动的类型，下面还注册了一个输入设备这里我的理解是这样的，input1主要是输出xyz方向上的重力加速度分量，而input2主要是用来输出一些碰撞和震动，还有横竖切换等事件。

下面是初始化文件系统

/*!
* This method is used to Initialize Sysfs. 
* client   : Pointer to i2c_client structure.
* return -EPERM  : Device pointer is NULL.
* return  0      : Success. 
*/
struct class *sensor_class_obj = NULL;
int InitializeSysfs(struct i2c_client *client)
{
	int RetVal = 0;
	int i = 0;
	int Iterator = 0;
	int Instance = 0;
	struct mxc_mma_device_t *pDev = i2c_get_clientdata(client);
	struct ChipInfo_t *pChip = pDev->pChip;
	struct SysfsInfo_t *pSysfsInfo = pChip->pSysfsInfo;

	if(pDev == NULL)
	{
		printk("%s: pDev => NULL pointer\r\n", __func__);
		return -EPERM;
	}

	if(sensor_class_obj == NULL)
	{
		pDev->class = class_create(THIS_MODULE, "sensor");
		if (IS_ERR(pDev->class)) 
		{
			printk(KERN_ERR "Unable to create class for Mxc MMA\n");
			RetVal = PTR_ERR(pDev->class);
		}
		sensor_class_obj = pDev->class;
	}
		else
	{
		pDev->class = sensor_class_obj;
	}
	client->dev.class = pDev->class;

	pDev->sys_device = device_create(pDev->class, NULL, MKDEV(pDev->major, 0), pDev,"mma");

	if (IS_ERR(pDev->sys_device))
       	{
		printk(KERN_ERR "Unable to create class device for Mxc Ipu\n");
		RetVal = PTR_ERR(pDev->sys_device);
		return RetVal;
	}

	dev_set_drvdata( (struct device *)&pDev->sys_device, pDev);

	for(Iterator = 0; Iterator < pChip->SysfsInfoSize; Iterator++)
	{
		for(Instance = 0; Instance < pSysfsInfo[Iterator].Instance; Instance++)
		{		
			/* Create motion_detection device */
			if(pSysfsInfo[Iterator].grpName != NULL)
			{
				pDev->sys_motion_dev = device_create(pDev->class, pDev->sys_device, MKDEV(0, 0), pDev,
						"%s%d", pSysfsInfo[Iterator].grpName, Instance);
			}
			else
			{
				pDev->sys_motion_dev = pDev->sys_device;
			}

			for(i=0; i < pSysfsInfo[Iterator].TotalEntries; i++)
			{
				if(sysfs_create_file(&pDev->sys_motion_dev->kobj, &pSysfsInfo[Iterator].AttrEntry[i].attr) < 0)
				printk("%s sys file creation failed.\r\n", pSysfsInfo[Iterator].AttrEntry[i].attr.name);
			}
		}
	}
	return RetVal;	
}
EXPORT_SYMBOL(sensor_class_obj);

这里代码很多，在mma_sysfs.c中，其实一点都不难，就是太多了有点复杂，看过内核驱动模型的同学应该很熟悉这里，这里就是建立了一个名为sensor的class，来作为这些文件的父类，具体的我不多说了，这里的文件太多了，也讲不完，可以一边参照data sheet一边看这里的文件时用来干嘛的，这里read/write 的时候就分别会回调这里相关的函数，然后去设置寄存器。大家可以看到下面就是这里建立的文件系统

/sys/class/sensor # ls -l
lrwxrwxrwx 1 root root 0 Jan 2 01:10 mma -> ../../devices/virtual/sensor/mma
lrwxrwxrwx 1 root root 0 Jan 2 01:10 motion_detection0 -> ../../devices/virtual/sensor/mma/motion_detection0
lrwxrwxrwx 1 root root 0 Jan 2 01:10 orientation_detection0 -> ../../devices/virtual/sensor/mma/orientation_detection0
lrwxrwxrwx 1 root root 0 Jan 2 01:10 tap_detection0 -> ../../devices/virtual/sensor/mma/tap_detection0
lrwxrwxrwx 1 root root 0 Jan 2 01:10 transient_detection0 -> ../../devices/virtual/sensor/mma/transient_detection0
/sys/class/sensor #

然后是初始化信号量和定时器，这里就不多说了。

接下来是创建了一个线程并执行他，这个线程是一个死循环，也就是我们这里最关键的一个函数，之后再说。

    if (plat_data->int1 > 0)  {   
	    set_irq_type(plat_data->int1, IRQF_TRIGGER_FALLING);

	    ret = request_irq(plat_data->int1, mma845x_interrupt,
			      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);

	    if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
			plat_data->int1, ret);
		goto error_disable_power;
	    }
    }
    else {
		gpChip->DisableInt(INT_EN_FIFO | INT_EN_DRDY);
		poll_mode = 1;
	}
    if (plat_data->int2 > 0){
    	 printk(KERN_INFO "%s:: Configuring interrupt IRQ [%d]\r\n", __func__,
	   plat_data->int2);

   	 set_irq_type(plat_data->int2, IRQF_TRIGGER_FALLING);
   	 ret = request_irq(plat_data->int2, mma845x_interrupt,
		      IRQF_TRIGGER_FALLING, DEVICE_NAME, pDev);
     if (ret) {
		dev_err(&client->dev, "request_irq(%d) returned error %d\n",
		plat_data->int2, ret);
		goto error_free_irq1;
     }

然后这里是申请中断，如果我们使用中断模式的话就申请中断，如果没有使用中断模式的话这里有一个flag，poll_mode被设置成1，初始化的时候是0.

porbe函数就先讲到这里，这里主要还是做了一些初始化的东西，下面来分析一下这个驱动是如何工作的，其实相关的就是这里最重要的2个东西，一个是定时器，还有一个是这个thread的处理，我们下面接着看

/*!
* This function implements interrupt handler routine 
* irq : Interrupt number
* dev_id
* return IRQ_RETVAL
*/
static irqreturn_t mma845x_interrupt(int irq, void *dev_id)
{
//+++add for debug
//printk("mma--irq\n");
    up(&chip_ready);
    return IRQ_RETVAL(1);
}

/*!
* This routine implements a call back for stall timer 
* data : Pointer to device data structure
* return NONE
*/
static void stall_timer_fn(unsigned long data)
{
//++++add for debug
//printk("mma-- poll\n");
    up(&chip_ready);
}

首先看下这里的中断响应函数和定时器响应函数，这里基本啥也没做，就是释放信号量，关键就在这，我们接着看

static int IntServiceThread(void *data)
{
    wait_queue_t    wait;
    int             ret = 0;
    struct mxc_mma_device_t *pDev = (struct mxc_mma_device_t *) data;
    struct ChipInfo_t *pChip = pDev->pChip;
    char buff[256];

    init_waitqueue_entry(&wait, current);

    mod_timer(&stall_timer, jiffies + (HZ));
    while (!done) {

	do {
	    ret = down_interruptible(&chip_ready);
	} while (ret == -EINTR);

	if (!poll_mode) {
		ret = pChip->GetIntSrc();
	} 
	else 
		ret = SRC_DRDY;


	if (SRC_DRDY & ret) {
	    pChip->Read(ACCL_DATA, (void *) buff);

	    UpdateAcclFiFo(buff);
	    if (!IsSuspended) {
		if (pDev->aflag == 1)
		    ReportEvent(pDev, ACCL_DATA, buff);
	    }
	}

	if (SRC_FIFO & ret) {
	    	int             count = 0,
			i = 0;
	    	char *pBuff = (char *) buff;
	    	printk(KERN_DEBUG "\t[FIFO] [%ld]\r\n", jiffies);
	    	count = pChip->Read(FIFO_DATA, (void *) buff);

	    	for (i = 0; i < count; i++) {
			UpdateAcclFiFo(pBuff + (i * sizeof(AcclData_t)));
			if (!IsSuspended) {
		    		if (pDev->aflag == 1)
					ReportEvent(pDev, ACCL_DATA,
				    	pBuff + (i * sizeof(AcclData_t)));
		}
	    }
	}

	/*
	 * Orientation 
	 */
	if (SRC_LNDPRT & ret) {
	    char           *pBuff = (char *) buff;
	    pChip->Read(ACCL_LNDPRT, (void *) buff);
	    if (!IsSuspended)
		ReportEvent(pDev, ACCL_LNDPRT, pBuff);
	}

	/*
	 * Motion / Freefall interrupt 
	 */
	if (SRC_FF_MT & ret) {
	    pChip->Read(ACCL_FF_MT, (void *) buff);
	    if (!IsSuspended)
		ReportEvent(pDev, ACCL_FF_MT, buff);
	}

	if (SRC_FF_MT_2 & ret) {
	    pChip->Read(ACCL_FF_MT_2, (void *) buff);
	    if (!IsSuspended)
		ReportEvent(pDev, ACCL_FF_MT_2, buff);
	}

	/*
	 * Motion / Freefall interrupt 
	 */
	if (SRC_PULSE & ret) {
	    pChip->Read(ACCL_PULSE, (void *) buff);
	    if (!IsSuspended)
		ReportEvent(pDev, ACCL_PULSE, buff);
	}

	if (SRC_TRANS & ret) {
	    pChip->Read(ACCL_TRANS, (void *) buff);
	    if (!IsSuspended)
		ReportEvent(pDev, ACCL_TRANS, buff);
	}
	if (!IsSuspended) {
		if (!poll_mode) {
		    mod_timer(&stall_timer, jiffies + (HZ));
		}
		else 
		    mod_timer(&stall_timer, jiffies + pChip->poll_time);
	}
	
    }
    return 0;
}

看下我们的线程，一开始是初始化了一堆变量，然后把data转化为我们这里的一个ChipInfo_t结构体指针，然后初始化等待队列，然后是修改定时器下次定时到达时间为1秒钟，然后是一个while循环，看下这个循环中到底做了啥事情。

首先是一个do while来试图获取信号量，这里信号量被初始化为0，所以这边是得不到的，就会一直等在这边，前面我们看过定时器和中断函数中都做了对信号量的释放动作，联想到这边就是说，我们的线程不是一直在走的，只有当发生定时器时间到达和中断发生了，才会让我们这里的线程继续往下走，也就实现了这里的polling和interrupt 这2中模式。

这个线程下面的代码我们都能猜到，就是通过I2C读取芯片中的数据，然后利用input子系统push到用户空间，如果是polling mode的话就修改下次定时到达的时间，这里的设计还是满巧妙的，有待学习，特别是我觉得代码写的比较规范。

下面来一张图来分析这里的处理流程。

画的太丑了，见谅！！