转载自: http://blog.csdn.net/yj4231/article/details/7751279
该系列文章将分为四个部分:
第一部分,将对SPI子系统整体进行描述,同时给出SPI的相关数据结构,最后描述SPI总线的注册。基于S3C2440的嵌入式Linux驱动——SPI子系统解读(一)
第二部分,该文将对SPI的主控制器(master)驱动进行描述。基于S3C2440的嵌入式Linux驱动——SPI子系统解读(二)
第三部分,即本篇文章,该文将对SPI设备驱动,也称protocol 驱动,进行讲解。
第四部分,通过SPI设备驱动留给用户层的API,我们将从上到下描述数据是如何通过SPI的protocol 驱动,由bitbang中转,最后由master驱动将数据传输出
去。 基于S3C2440的嵌入式Linux驱动——SPI子系统解读(四)
本文属于第三部分。
5. SPI设备驱动
在主控制器驱动中,spi_device已经注册了,在设备驱动中,首先要做的就是注册spi_driver,并提供用户层相应的API。
5.1 SPI设备驱动的注册
下列数据结构及函数位于drivers/spi/spidev.c。
static struct file_operations spidev_fops = { .owner = THIS_MODULE, /* REVISIT switch to aio primitives, so that userspace * gets more complete API coverage. It'll simplify things * too, except for the locking. */ .write = spidev_write, .read = spidev_read, .unlocked_ioctl = spidev_ioctl, .open = spidev_open, .release = spidev_release, }; /* The main reason to have this class is to make mdev/udev create the * /dev/spidevB.C character device nodes exposing our userspace API. * It also simplifies memory management. */ static struct class *spidev_class; static struct spi_driver spidev_spi = { .driver = { .name = "spidev", .owner = THIS_MODULE, }, .probe = spidev_probe, .remove = __devexit_p(spidev_remove), /* NOTE: suspend/resume methods are not necessary here. * We don't do anything except pass the requests to/from * the underlying controller. The refrigerator handles * most issues; the controller driver handles the rest. */ }; static int __init spidev_init(void) { int status; /* Claim our 256 reserved device numbers. Then register a class * that will key udev/mdev to add/remove /dev nodes. Last, register * the driver which manages those device numbers. */ BUILD_BUG_ON(N_SPI_MINORS > 256); /*检查次设备号*/ status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops); /*注册字符设备,major=153*/ if (status < 0) return status; spidev_class = class_create(THIS_MODULE, "spidev"); /*创建sysfs入口,spidev类*/ if (IS_ERR(spidev_class)) { unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name); return PTR_ERR(spidev_class); } status = spi_register_driver(&spidev_spi); /*注册spi_driver,并调用probe方法*/ if (status < 0) { class_destroy(spidev_class); /* 在sysfs中移除spidev_class目录*/ unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name); } return status; } module_init(spidev_init); static void __exit spidev_exit(void) { spi_unregister_driver(&spidev_spi); /*注销spi_driver*/ class_destroy(spidev_class); /*注销类*/ unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name);/*注销字符设备*/ } module_exit(spidev_exit);该函数中,创建了一个字符设备以提供API给用户层,同时创建了一个spidev类,最后注册spi_driver到内核中。
在这里我们看到了SPI设备驱动是如何提供API给用户层的,那就是通过再熟悉不过的字符设备。通过字符设备,给用户层提供了5个API:open,release,write,read和ioctl。本文在后面将介绍open和close,剩余3个将在本系列的第四篇文章中介绍。
接着看下spi_register_driver函数, 该函数位于drivers/spi/spidev.c。
/** * 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); } EXPORT_SYMBOL_GPL(spi_register_driver);在调用driver_register的过程中,将用driver.name和spi_device的modalias字段进行比较,两者相等则将该spi_driver和spi_device进行绑定。
当spi_driver注册成功以后,将调用probe方法:spidev_probe函数。
5.2 probe方法
我们来看看spidev_probe这个函数,该函数位于drivers/spi/spidev.c。
#define SPIDEV_MAJOR 153 /* assigned */ #define N_SPI_MINORS 32 /* ... up to 256 */ static unsigned long minors[N_SPI_MINORS / BITS_PER_LONG]; /**/ static LIST_HEAD(device_list); static DEFINE_MUTEX(device_list_lock); static int spidev_probe(struct spi_device *spi) { struct spidev_data *spidev; int status; unsigned long minor; /* Allocate driver data */ spidev = kzalloc(sizeof(*spidev), GFP_KERNEL); /*以kmalloc分配内存,并清0*/ if (!spidev) return -ENOMEM; /* Initialize the driver data */ spidev->spi = spi; /*保存spi_device*/ spin_lock_init(&spidev->spi_lock); /*初始化自旋锁*/ mutex_init(&spidev->buf_lock); /*初始化互斥体*/ INIT_LIST_HEAD(&spidev->device_entry); /*初始化链表头,链表为双向循环链表*/ /* If we can allocate a minor number, hook up this device. * Reusing minors is fine so long as udev or mdev is working. */ mutex_lock(&device_list_lock); /*上锁*/ minor = find_first_zero_bit(minors, N_SPI_MINORS); /*分配次设备号*/ if (minor < N_SPI_MINORS) { struct device *dev; spidev->devt = MKDEV(SPIDEV_MAJOR, minor); /*根据主次设备号来获取设备号*/ dev = device_create(spidev_class, &spi->dev, spidev->devt, /*创建设备节点*/ spidev, "spidev%d.%d", spi->master->bus_num, spi->chip_select); status = IS_ERR(dev) ? PTR_ERR(dev) : 0; } else { dev_dbg(&spi->dev, "no minor number available!\n"); status = -ENODEV; } if (status == 0) { set_bit(minor, minors); /*保存已使用的次设备号*/ list_add(&spidev->device_entry, &device_list);/*在链表头list后面添加entry*/ } mutex_unlock(&device_list_lock);/*解锁互斥体*/ if (status == 0) spi_set_drvdata(spi, spidev);/*spi->dev.driver_data=spidev*/ else kfree(spidev); return status; }其中用到的的 struct spidev_data 结构如下:
struct spidev_data { dev_t devt; spinlock_t spi_lock; struct spi_device *spi; struct list_head device_entry; /* buffer is NULL unless this device is open (users > 0) */ struct mutex buf_lock; unsigned users; u8 *buffer; };
这个函数中,分配了spidev_data和次设备号,随后根据主次设备号创建了设备节点。设备节点的名字是spidev“bus_num””.chip_select",意思就是该设备是在第几个SPI接口上的第几个设备。
此外,将spidev添加到device_list中,这样做就方便查找该spidev。
5.3 remove方法
下列函数位于drivers/spi/spidev.c。
static int spidev_remove(struct spi_device *spi) { struct spidev_data *spidev = spi_get_drvdata(spi); /* make sure ops on existing fds can abort cleanly */ spin_lock_irq(&spidev->spi_lock); spidev->spi = NULL; spi_set_drvdata(spi, NULL); spin_unlock_irq(&spidev->spi_lock); /* prevent new opens */ mutex_lock(&device_list_lock); list_del(&spidev->device_entry); /*删除entry*/ device_destroy(spidev_class, spidev->devt); /*删除设备节点*/ clear_bit(MINOR(spidev->devt), minors);/*删除使用的次设备号信息*/ if (spidev->users == 0) kfree(spidev); mutex_unlock(&device_list_lock); return 0; }6. open和release
接着来看下open和release系统调用的API接口,其余3个接口将在本系列的第四篇文章中给出。
6.1 open方法
下列函数位于drivers/spi/spidev.c。
static int spidev_open(struct inode *inode, struct file *filp) { struct spidev_data *spidev; int status = -ENXIO; lock_kernel(); /*加锁大内核锁,可以睡眠,只能在进程上下文使用*/ mutex_lock(&device_list_lock); /*加锁互斥体*/ list_for_each_entry(spidev, &device_list, device_entry) {/*从list开始遍历entry,即遍历所有的spidev*/ if (spidev->devt == inode->i_rdev) { /*判断设备号是否相等*/ status = 0; /*找到匹配的spi设备*/ break; } } if (status == 0) { /*NOTE:多个程序调用open方法,但他们共享一个buffer,因此对buufer需要进行互斥保护*/ if (!spidev->buffer) { /*buffer为空*/ spidev->buffer = kmalloc(bufsiz, GFP_KERNEL);/*分配buffer缓冲区,默认4KB*/ if (!spidev->buffer) { dev_dbg(&spidev->spi->dev, "open/ENOMEM\n"); status = -ENOMEM; } } if (status == 0) { spidev->users++; /*成功open以后,增加用户计数*/ filp->private_data = spidev; /*保存spidev指针*/ nonseekable_open(inode, filp); /*禁用lseek*/ } } else pr_debug("spidev: nothing for minor %d\n", iminor(inode)); mutex_unlock(&device_list_lock);/*释放互斥体*/ unlock_kernel(); /*释放大内核锁*/ return status; }
6.2 release方法
下列函数位于drivers/spi/spidev.c。
static int spidev_release(struct inode *inode, struct file *filp) { struct spidev_data *spidev; int status = 0; mutex_lock(&device_list_lock); /*加锁互斥体*/ spidev = filp->private_data; /*获取spidev*/ filp->private_data = NULL; /* last close? */ spidev->users--; /*关闭设备文件,减少用户计数*/ if (!spidev->users) { /*如果用户数为0*/ int dofree; kfree(spidev->buffer); /*释放缓冲区*/ spidev->buffer = NULL; /* ... after we unbound from the underlying device? */ spin_lock_irq(&spidev->spi_lock); /*加锁互斥体*/ dofree = (spidev->spi == NULL); /*????*/ spin_unlock_irq(&spidev->spi_lock); /*释放互斥体*/ if (dofree) kfree(spidev); /*释放spidev,在probe中分配*/ } mutex_unlock(&device_list_lock);/*释放互斥体*/ return status; }至此,对于protocol驱动层的框架进行了简单的分析,在下一篇将对该驱动层很多未分析的函数进行一一讲解。下一篇的内容非常的重要哦。