Linux下MCP2515驱动解析 .

拿到一个设备驱动，首先要看的是设备初始化函数。

static int __init mcp251x_init(void)
{
    int ret;
    can_class = class_create(THIS_MODULE, "can");
    if (IS_ERR(can_class))
        return PTR_ERR(can_class);
    ret = alloc_chrdev_region(&devid, 0, CAN_DEV_MAX, DRIVER_NAME);
    if (ret < 0)
    {
        printk(KERN_ERR "%s: failed to allocate char dev region\n", __FILE__);
        class_destroy(can_class);
        return ret;
    }

    return spi_register_driver(&mcp251x_driver);
}

static int __init mcp251x_init(void)
{
    int ret;
    can_class = class_create(THIS_MODULE, "can");
    if (IS_ERR(can_class))
        return PTR_ERR(can_class);
    ret = alloc_chrdev_region(&devid, 0, CAN_DEV_MAX, DRIVER_NAME);
    if (ret < 0)
    {
        printk(KERN_ERR "%s: failed to allocate char dev region\n", __FILE__);
        class_destroy(can_class);
        return ret;
    }

    return spi_register_driver(&mcp251x_driver);
}

class_create()用于自动创建设备节点，我们可以暂时不看，有兴趣的可以看看Linux源码。alloc_chrdev_region()自动为DRIVER_NAME分配设备号。在这里，我们真正关心的是spi_register_driver()函数和mcp251x_driver结构体的内容。
我们先看spi_register_driver()的内容。

/**
 * spi_register_driver - register a SPI driver
 * @sdrv: the driver to register
 * Context: can sleep
 */
int spi_register_driver(struct spi_driver *sdrv)
{
    sdrv->driver.bus = &spi_bus_type;
    if (sdrv->probe)
        sdrv->driver.probe = spi_drv_probe;
    if (sdrv->remove)
        sdrv->driver.remove = spi_drv_remove;
    if (sdrv->shutdown)
        sdrv->driver.shutdown = spi_drv_shutdown;
    return driver_register(&sdrv->driver);
}

/**
 * spi_register_driver - register a SPI driver
 * @sdrv: the driver to register
 * Context: can sleep
 */
int spi_register_driver(struct spi_driver *sdrv)
{
	sdrv->driver.bus = &spi_bus_type;
	if (sdrv->probe)
		sdrv->driver.probe = spi_drv_probe;
	if (sdrv->remove)
		sdrv->driver.remove = spi_drv_remove;
	if (sdrv->shutdown)
		sdrv->driver.shutdown = spi_drv_shutdown;
	return driver_register(&sdrv->driver);
}

spi_register_driver()完成了驱动在总线的挂载以及spi驱动函数probe, remove, shutdown的赋值。那mcp251x_driver是什么样的结构体，里面又存储了什么内容呢？

static struct spi_driver mcp251x_driver = {
    .driver = {
               .name = DRIVER_NAME,
               .bus = &spi_bus_type,
               .owner = THIS_MODULE,
               },
    .probe = mcp251x_probe,
    .remove = __devexit_p(mcp251x_remove),
#ifdef CONFIG_PM
    .suspend = mcp251x_suspend,
    .resume = mcp251x_resume,
#endif
};

static struct spi_driver mcp251x_driver = {
    .driver = {
               .name = DRIVER_NAME,
               .bus = &spi_bus_type,
               .owner = THIS_MODULE,
               },
    .probe = mcp251x_probe,
    .remove = __devexit_p(mcp251x_remove),
#ifdef CONFIG_PM
    .suspend = mcp251x_suspend,
    .resume = mcp251x_resume,
#endif
};

mcp251x_driver是结构体spi_driver的实例，在mcp251x_driver里面完成了mcp251x驱动函数probe, remove, suspend, resume的赋值。

在进入mcp251x的驱动函数之前，我们还是先看看mcp251x的结构吧！

struct mcp251x
{
    struct cdev cdev;
    struct class_device *class_dev;
    struct semaphore lock;      /* semaphore for spi bus share. */
    struct semaphore rxblock;   /* semaphore for ring buffer of receive. */
    struct semaphore txblock;   /* semaphore for ring buffer of send. */

    uint8_t *spi_transfer_buf;  /* temp buffer for spi bus transfer. */

    struct can_frame rxb[MCP251X_BUF_LEN];  /* ring buffer for receive. */
    struct can_frame txb[MCP251X_BUF_LEN];  /* ring buffer for send. */

    int txbin;                  /* pos of in for ring buffer of sned. */
    int txbout;                 /* pos of out for ring buffer of send. */
    int rxbin;                  /* pos of in for ring buffer of receive. */
    int rxbout;                 /* pos of out for ring buffer of receive. */

    int bit_rate;               /* save bit rate of current set. */
    int count;                  /* count of the device opened. */

    wait_queue_head_t wq;       /* queue for read process. */

    struct work_struct irq_work;    /* bottom half of interrupt task. */

    struct spi_device *spi;     /* save the point of struce spi_device. */
    struct can_filter filter;   /* save the filter data of current set. */
};

struct mcp251x
{
    struct cdev cdev;
    struct class_device *class_dev;
    struct semaphore lock;      /* semaphore for spi bus share. */
    struct semaphore rxblock;   /* semaphore for ring buffer of receive. */
    struct semaphore txblock;   /* semaphore for ring buffer of send. */

    uint8_t *spi_transfer_buf;  /* temp buffer for spi bus transfer. */

    struct can_frame rxb[MCP251X_BUF_LEN];  /* ring buffer for receive. */
    struct can_frame txb[MCP251X_BUF_LEN];  /* ring buffer for send. */

    int txbin;                  /* pos of in for ring buffer of sned. */
    int txbout;                 /* pos of out for ring buffer of send. */
    int rxbin;                  /* pos of in for ring buffer of receive. */
    int rxbout;                 /* pos of out for ring buffer of receive. */

    int bit_rate;               /* save bit rate of current set. */
    int count;                  /* count of the device opened. */

    wait_queue_head_t wq;       /* queue for read process. */

    struct work_struct irq_work;    /* bottom half of interrupt task. */

    struct spi_device *spi;     /* save the point of struce spi_device. */
    struct can_filter filter;   /* save the filter data of current set. */
};

其中的很多结构体，我们暂时不管。下面开始进入正题。

static int __devinit mcp251x_probe(struct spi_device *spi)
{
    struct mcp251x *chip;
    int ret = 0;

    dev_dbg(&spi->dev, "%s: start\n", __FUNCTION__);

    /* 申请内存资源 */
    chip = kmalloc(sizeof(struct mcp251x), GFP_KERNEL);
    if (!chip)
    {
        ret = -ENOMEM;
        goto error_alloc;
    }

    /* 将mcp251x的设备信息保存到spi的设备结构体中 */
    dev_set_drvdata(&spi->dev, chip);

    /* mcp251x结构体初始化 */
    chip->txbin = chip->txbout = 0;
    chip->rxbin = chip->rxbout = 0;
    chip->count = 0;
    chip->spi = spi;
    init_MUTEX(&chip->lock);
    init_MUTEX(&chip->txblock);
    init_MUTEX(&chip->rxblock);
    init_waitqueue_head(&chip->wq);

#if (LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,20))
    INIT_WORK(&chip->irq_work, mcp251x_irq_handler);
#else
    INIT_WORK(&chip->irq_work, mcp251x_irq_handler, spi);
#endif

    /* 为spi的buf分配空间 */
    chip->spi_transfer_buf = kmalloc(SPI_TRANSFER_BUF_LEN, GFP_KERNEL);
    if (!chip->spi_transfer_buf)
    {
        ret = -ENOMEM;
        goto error_buf;
    }

    /* 输入模式，不使用内部上拉电阻 */
    at91_set_gpio_input(spi->irq, 0);
    /* 绑定输入函数mcp251x_irq，传递参数spi */
    /* mcp251x_irq函数我们等下再看，先放一放 */
    ret = request_irq(spi->irq, mcp251x_irq, IRQF_SAMPLE_RANDOM, DRIVER_NAME, spi);
    if (ret < 0)
    {
        dev_err(&spi->dev, "request irq %d failed (ret = %d)\n", spi->irq, ret);
        goto error_irq;
    }

    if (can_minor > CAN_DEV_MAX)
        goto error_register;

    if (can_major)
    {
        devid = MKDEV(can_major, can_minor++);
        ret = register_chrdev_region(devid, 0, DRIVER_NAME);
    }
    else
    {
        ret = alloc_chrdev_region(&devid, can_minor, 0, DRIVER_NAME);
        can_major = MAJOR(devid);
    }

    if (ret < 0)
    {
        dev_err(&spi->dev, "register char device region (%d:%d) failed (ret = %d)\n", MAJOR(devid),
                MINOR(devid), ret);
        goto error_register;
    }

    /* 字符设备的初始化以及添加到内核 */
    cdev_init(&chip->cdev, &mcp251x_fops);
    chip->cdev.owner = THIS_MODULE;
    ret = cdev_add(&chip->cdev, devid, 1);
    if (ret < 0)
    {
        dev_err(&spi->dev, "register char device failed (ret = %d)\n", ret);
        goto error_devadd;
    }

    dev_info(&spi->dev, "device register at dev(%d:%d)\n", MAJOR(devid), MINOR(devid));

    /* 自动创建设备文件 */
    chip->class_dev = device_create(can_class, NULL,
                                    MKDEV(MAJOR(devid), can_minor), &spi->dev, "can%d", can_minor);
    if (IS_ERR(chip->class_dev))
    {
        dev_err(&spi->dev, "cannot create CAN class device\n");
        ret = PTR_ERR(chip->class_dev);
        goto error_class_reg;
    }

    /* mcp251x初始化设置 */
    mcp251x_hw_init(spi);
    mcp251x_set_bit_rate(spi, 125000);  /* A reasonable default */
    mcp251x_hw_sleep(spi);

    return 0;

  error_class_reg:
    cdev_del(&chip->cdev);
  error_devadd:
    unregister_chrdev_region(devid, 0);
  error_register:
    free_irq(spi->irq, spi);
  error_irq:
    kfree(chip->spi_transfer_buf);
  error_buf:
    kfree(chip);
  error_alloc:
    return ret;
}