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. */
};- 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;
- }