linux SPI 设备驱动
由内核提供，位于drivers/spi/spidev.c
/* * spidev.c -- simple synchronous userspace interface to SPI devices * * Copyright (C) 2006 SWAPP * Andrea Paterniani <[email protected]> * Copyright (C) 2007 David Brownell (simplification, cleanup) * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include <linux/init.h> #include <linux/module.h> #include <linux/ioctl.h> #include <linux/fs.h> #include <linux/device.h> #include <linux/list.h> #include <linux/errno.h> #include <linux/mutex.h> #include <linux/slab.h> #include <linux/spi/spi.h> #include <linux/spi/spidev.h> #include <asm/uaccess.h> /* * This supports acccess to SPI devices using normal userspace I/O calls. * Note that while traditional UNIX/POSIX I/O semantics are half duplex, * and often mask message boundaries, full SPI support requires full duplex * transfers. There are several kinds of of internal message boundaries to * handle chipselect management and other protocol options. * * SPI has a character major number assigned. We allocate minor numbers * dynamically using a bitmask. You must use hotplug tools, such as udev * (or mdev with busybox) to create and destroy the /dev/spidevB.C device * nodes, since there is no fixed association of minor numbers with any * particular SPI bus or device. */ #define SPIDEV_MAJOR 153 /* assigned */ #define N_SPI_MINORS 32 /* ... up to 256 */ static unsigned long minors[N_SPI_MINORS / BITS_PER_LONG]; /* Bit masks for spi_device.mode management. Note that incorrect * settings for CS_HIGH and 3WIRE can cause *lots* of trouble for other * devices on a shared bus: CS_HIGH, because this device will be * active when it shouldn't be; 3WIRE, because when active it won't * behave as it should. * * REVISIT should changing those two modes be privileged? */ #define SPI_MODE_MASK (SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \ | SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP) struct spidev_data { struct device dev; struct spi_device *spi; struct list_head device_entry; struct mutex buf_lock; unsigned users; u8 *buffer; }; static LIST_HEAD(device_list); static DEFINE_MUTEX(device_list_lock); static unsigned bufsiz = 4096; module_param(bufsiz, uint, S_IRUGO); MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message"); /*-------------------------------------------------------------------------*/ /* Read-only message with current device setup */ static ssize_t spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos) { struct spidev_data *spidev; struct spi_device *spi; ssize_t status = 0; /* chipselect only toggles at start or end of operation */ if (count > bufsiz) return -EMSGSIZE; spidev = filp->private_data; spi = spidev->spi; mutex_lock(&spidev->buf_lock); status = spi_read(spi, spidev->buffer, count); if (status == 0) { unsigned long missing; missing = copy_to_user(buf, spidev->buffer, count); if (count && missing == count) status = -EFAULT; else status = count - missing; } mutex_unlock(&spidev->buf_lock); return status; } /* Write-only message with current device setup */ static ssize_t spidev_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos) { struct spidev_data *spidev; struct spi_device *spi; ssize_t status = 0; unsigned long missing; /* chipselect only toggles at start or end of operation */ if (count > bufsiz) return -EMSGSIZE; spidev = filp->private_data; spi = spidev->spi; mutex_lock(&spidev->buf_lock); missing = copy_from_user(spidev->buffer, buf, count); if (missing == 0) { status = spi_write(spi, spidev->buffer, count); if (status == 0) status = count; } else status = -EFAULT; mutex_unlock(&spidev->buf_lock); return status; } static int spidev_message(struct spidev_data *spidev, struct spi_ioc_transfer *u_xfers, unsigned n_xfers) { struct spi_message msg; struct spi_transfer *k_xfers; struct spi_transfer *k_tmp; struct spi_ioc_transfer *u_tmp; struct spi_device *spi = spidev->spi; unsigned n, total; u8 *buf; int status = -EFAULT; spi_message_init(&msg); k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);/*分配n个spi_transfer的内存空间，一个spi_message由多个数据段spi_message组成*/ if (k_xfers == NULL) return -ENOMEM; /* Construct spi_message, copying any tx data to bounce buffer. * We walk the array of user-provided transfers, using each one * to initialize a kernel version of the same transfer. */ mutex_lock(&spidev->buf_lock); buf = spidev->buffer; total = 0; /*这个for循环的主要任务是将所有的spi_transfer组装成一个spi_message*/ for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers; n; n--, k_tmp++, u_tmp++) { k_tmp->len = u_tmp->len;/*u_tmp是从用户空间传下来的spi_ioc_message的大小，spi_ioc_message是对spi_message的映射*/ /*统计要传输数据的总量*/ total += k_tmp->len; if (total > bufsiz) { status = -EMSGSIZE; goto done; } /*spi_transfer是一个读写的buffer对，如果是要接收则把buffer给接收的rx_buf*/ if (u_tmp->rx_buf) { k_tmp->rx_buf = buf; if (!access_ok(VERIFY_WRITE, (u8 __user *) (uintptr_t) u_tmp->rx_buf, u_tmp->len)) goto done; } if (u_tmp->tx_buf) {/*如果要传输，这个buffer给tx_buf使用，从用户空间拷过来要传输的数据*/ k_tmp->tx_buf = buf; if (copy_from_user(buf, (const u8 __user *) (uintptr_t) u_tmp->tx_buf, u_tmp->len)) goto done; } buf += k_tmp->len;/*指向下一段内存*/ k_tmp->cs_change = !!u_tmp->cs_change; /*最后一个transfer传输完毕是否会影响片选*/ k_tmp->bits_per_word = u_tmp->bits_per_word; /*每字长的字节数*/ k_tmp->delay_usecs = u_tmp->delay_usecs;/*一段数据传输完需要一定的时间等待*/ k_tmp->speed_hz = u_tmp->speed_hz; /*初始化传输速度*/ #ifdef VERBOSE dev_dbg(&spi->dev, " xfer len %zd %s%s%s%dbits %u usec %uHz\n", u_tmp->len, u_tmp->rx_buf ? "rx " : "", u_tmp->tx_buf ? "tx " : "", u_tmp->cs_change ? "cs " : "", u_tmp->bits_per_word ? : spi->bits_per_word, u_tmp->delay_usecs, u_tmp->speed_hz ? : spi->max_speed_hz); #endif spi_message_add_tail(k_tmp, &msg); /*将spi_transfer通过它的transfer_list字段挂到spi_message的transfer队列上*/ } status = spi_sync(spi, &msg);/*同步*/ if (status < 0) goto done; /* copy any rx data out of bounce buffer */ buf = spidev->buffer; for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {/*把传输数据拷贝到用户空间打印出来，可以查看是否传输成功*/ if (u_tmp->rx_buf) { if (__copy_to_user((u8 __user *) (uintptr_t) u_tmp->rx_buf, buf, u_tmp->len)) { status = -EFAULT; goto done; } } buf += u_tmp->len; } status = total; done: mutex_unlock(&spidev->buf_lock); kfree(k_xfers); return status; } static int spidev_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg) { int err = 0; int retval = 0; struct spidev_data *spidev; struct spi_device *spi; u32 tmp; unsigned n_ioc; struct spi_ioc_transfer *ioc; /* Check type and command number */ if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)/*如果幻数不想等，则报错，查看这个命令的幻数字段是否为'k'*/ return -ENOTTY; /* Check access direction once here; don't repeat below. * IOC_DIR is from the user perspective, while access_ok is * from the kernel perspective; so they look reversed. *//*对用户空间的指针进行检查，分成读写两部分检查*/ if (_IOC_DIR(cmd) & _IOC_READ)/*如果方向是用户空间从内核读，即内核向用户空间写，则检查用户空间的地址是否有效*/ err = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd)); if (err == 0 && _IOC_DIR(cmd) & _IOC_WRITE)/*如果方向是用户空间向内核写，即内核读用户空间，则检查用户空间的地址是否有效*/ err = !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd)); if (err) return -EFAULT; spidev = filp->private_data; spi = spidev->spi; switch (cmd) { /* read requests */ case SPI_IOC_RD_MODE: retval = __put_user(spi->mode & SPI_MODE_MASK, (__u8 __user *)arg); break; case SPI_IOC_RD_LSB_FIRST: retval = __put_user((spi->mode & SPI_LSB_FIRST) ? 1 : 0, (__u8 __user *)arg); break; case SPI_IOC_RD_BITS_PER_WORD: retval = __put_user(spi->bits_per_word, (__u8 __user *)arg); break; case SPI_IOC_RD_MAX_SPEED_HZ: retval = __put_user(spi->max_speed_hz, (__u32 __user *)arg); break; /* write requests */ case SPI_IOC_WR_MODE: retval = __get_user(tmp, (u8 __user *)arg); if (retval == 0) { u8 save = spi->mode;/*先将之前的模式保存起来，一旦设置失败进行回复*/ if (tmp & ~SPI_MODE_MASK) { retval = -EINVAL; break; } tmp |= spi->mode & ~SPI_MODE_MASK; spi->mode = (u8)tmp; retval = spi_setup(spi); if (retval < 0) spi->mode = save; else dev_dbg(&spi->dev, "spi mode %02x\n", tmp); } break; case SPI_IOC_WR_LSB_FIRST: retval = __get_user(tmp, (__u8 __user *)arg); if (retval == 0) { u8 save = spi->mode; if (tmp) spi->mode |= SPI_LSB_FIRST; else spi->mode &= ~SPI_LSB_FIRST; retval = spi_setup(spi); if (retval < 0) spi->mode = save; else dev_dbg(&spi->dev, "%csb first\n", tmp ? 'l' : 'm'); } break; case SPI_IOC_WR_BITS_PER_WORD: retval = __get_user(tmp, (__u8 __user *)arg); if (retval == 0) { u8 save = spi->bits_per_word; spi->bits_per_word = tmp; retval = spi_setup(spi); if (retval < 0) spi->bits_per_word = save; else dev_dbg(&spi->dev, "%d bits per word\n", tmp); } break; case SPI_IOC_WR_MAX_SPEED_HZ: retval = __get_user(tmp, (__u32 __user *)arg); if (retval == 0) { u32 save = spi->max_speed_hz; spi->max_speed_hz = tmp; retval = spi_setup(spi); if (retval < 0) spi->max_speed_hz = save; else dev_dbg(&spi->dev, "%d Hz (max)\n", tmp); } break; default: /* segmented and/or full-duplex I/O request */ if (_IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0)) || _IOC_DIR(cmd) != _IOC_WRITE) return -ENOTTY; tmp = _IOC_SIZE(cmd); /*得到用户空间数据的大小*/ if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) { /*如果这些数据不能分成spi_ioc_transfer的整数倍，则不能进行传输，spi_io_transfer是对spi_transfer的映射*/ retval = -EINVAL; break; } n_ioc = tmp / sizeof(struct spi_ioc_transfer);/*计算出能分多少个spi_ioc_transfer*/ if (n_ioc == 0) break; /* copy into scratch area */ ioc = kmalloc(tmp, GFP_KERNEL); if (!ioc) { retval = -ENOMEM; break; } if (__copy_from_user(ioc, (void __user *)arg, tmp)) {/*把用户空间的数据拷贝过来*/ kfree(ioc); retval = -EFAULT; break; } /* translate to spi_message, execute */ retval = spidev_message(spidev, ioc, n_ioc);/*进行数据传输*/ kfree(ioc); break; } return retval; } static int spidev_open(struct inode *inode, struct file *filp) { struct spidev_data *spidev; int status = -ENXIO; mutex_lock(&device_list_lock); 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->dev.devt == inode->i_rdev) { /*判断设备号是否相等*/ status = 0;/*相等*/ break; } } if (status == 0) {/*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) { spidev->buffer = kmalloc(bufsiz, GFP_KERNEL); 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*/ return status; }/*在这里，以device_list为链表头，遍历所有的spidev_data结构，通过设备节点的设备号和spidev_data中保存的设备号进行匹配，来找到属于该设备节点的spi设备。随后，分配了spi设备驱动层所使用的缓冲区，最后增加打开计数。*/ static int spidev_release(struct inode *inode, struct file *filp) { struct spidev_data *spidev; int status = 0; mutex_lock(&device_list_lock); spidev = filp->private_data; filp->private_data = NULL; spidev->users--; if (!spidev->users) { kfree(spidev->buffer); spidev->buffer = NULL; } mutex_unlock(&device_list_lock); return status; } 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, .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 void spidev_classdev_release(struct device *dev) { struct spidev_data *spidev; spidev = container_of(dev, struct spidev_data, dev); kfree(spidev); } static struct class spidev_class = { .name = "spidev", .owner = THIS_MODULE, .dev_release = spidev_classdev_release, }; /*-------------------------------------------------------------------------*/ 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; mutex_init(&spidev->buf_lock); 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); minor = find_first_zero_bit(minors, N_SPI_MINORS);/*分配次设备号*/ if (minor < N_SPI_MINORS) { spidev->dev.parent = &spi->dev; spidev->dev.class = &spidev_class; spidev->dev.devt = MKDEV(SPIDEV_MAJOR, minor);/*根据主次设备号来获取设备号*/ snprintf(spidev->dev.bus_id, sizeof spidev->dev.bus_id, "spidev%d.%d", spi->master->bus_num, spi->chip_select); status = device_register(&spidev->dev);/*创建设备节点*/ } 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*/ dev_set_drvdata(&spi->dev, spidev); list_add(&spidev->device_entry, &device_list); } mutex_unlock(&device_list_lock); if (status != 0) kfree(spidev); return status; } static int spidev_remove(struct spi_device *spi) { struct spidev_data *spidev = dev_get_drvdata(&spi->dev); mutex_lock(&device_list_lock); list_del(&spidev->device_entry);/*删除entry*/ dev_set_drvdata(&spi->dev, NULL);/*删除设备节点*/ clear_bit(MINOR(spidev->dev.devt), minors);/*删除使用的次设备号信息*/ device_unregister(&spidev->dev); mutex_unlock(&device_list_lock); return 0; } 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; status = class_register(&spidev_class);/*创建spidev类*/ if (status < 0) { unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name); return status; } status = spi_register_driver(&spidev_spi);/*注册spi_driver,并调用probe方法*/ if (status < 0) { class_unregister(&spidev_class); 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); class_unregister(&spidev_class); unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name); } module_exit(spidev_exit); MODULE_AUTHOR("Andrea Paterniani, <[email protected]>"); MODULE_DESCRIPTION("User mode SPI device interface"); MODULE_LICENSE("GPL");
SPI 设备驱动主要完成用户空间调用的open,close,read,write,ioctl的具体实现。其中open和close相对来说比较简单，看注释就可以。在spi设备驱动层提供了两种数据传输方式。一种是半双工方式，write方法提供了半双工读访问，read方法提供了半双工写访问。另一种就是全双工方式，ioctl调用将同时完成数据的传送与发送。
1.write，read
从示意图中，我们可以很清除看到函数的调用过程：先调用spi设备驱动层，随后调用bitbang中间层，最后调用了master驱动层来完成数据的传输。
在spi_write中（spi.h）创建了transfer和message。spi_transfer包含了要发送数据的信息。然后初始化了message中的transfer链表头，并将spi_transfer添加到了transfer链表中。也就是以spi_message的transfers为链表头的链表中，包含了transfer，而transfer正好包含了需要发送的数据。由此可见message其实是对transfer的封装。
在spi_sync（spi.h），将spi_complete和done封装到message中去。这个东东将实现write系统调用的同步。随后调用了spi_async，从名字上可以看出该函数是异步的，也就是说该函数返回后，数据并没有被发送出去。因此使用了wait_for_completion来等待数据的发送完成，达到同步的目的。
在 spi_async（spi.h）仅仅保存了spi_device信息后，然后调用了master的transfer方法，该方法在spi_bitbang_start中定义为spi_bitbang_transfer。
spi_bitbang_transfer位于drivers/spi/spi_bitbang.c，属于内核层了，在此不做分析。
2.ioctl
在spidev_ioctl中，首先对cmd进行了一些列的检查。随后使用switch语句来判读cmd，并执行相应的功能。cmd的第一部分为读请求，分别从寄存器读取4个参数。第二部分为写请求，分别用于修改4个参数并写入寄存器。剩余的第三部分就是全双工读写请求，这是会先计算共有多少个spi_ioc_transfer，然后分配空间，从用户空间将spi_ioc_transfer数组拷贝过来，然后将该数组和数组个数作为参数调用spidev_message。
在spidev_message 中，根据spi_ioc_transfer的个数，分配了同样个数的spi_transfer，把spi_ioc_transfer中的信息复制给spi_transfer，然后将spi_transfer添加到spi_message的链表中。接着。执行了spidev_sync，从spidev_sync返回以后，数据传输完毕，将读取到的数据，复制到用户空间。
