spidev_init源码分析
register_chrdev：创建字符设备，spi属于字符设备驱动，定义如下：
static inline int register_chrdev(unsigned int major, const char *name,
const struct file_operations *fops)
入参传入 file_operations 结构体，结构体存了很多函数指针，实现读写和ioctrl相关操作，也是驱动最核心的功能，下面是spidev 实现的结构体：
static const 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, /* 单工写模式 */
.read = spidev_read, /* 单工读模式 */
.unlocked_ioctl = spidev_ioctl, /* 设置频率、模式、进行双工传输 */
.compat_ioctl = spidev_compat_ioctl,
.open = spidev_open,
.release = spidev_release,
.llseek = no_llseek,
};
spidev_fops分析
spiev_write函数分析
spidev_write的源码如下：
/* 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;
ssize_t status;
unsigned long missing;
/* chipselect only toggles at start or end of operation */
if (count > bufsiz)
return -EMSGSIZE;
spidev = filp->private_data; /* spidev_data结构体是很重要的数据传递类型 */
mutex_lock(&spidev->buf_lock);
missing = copy_from_user(spidev->tx_buffer, buf, count); /* 数据从用户态copy到内核态 */
if (missing == 0)
status = spidev_sync_write(spidev, count); /* 同步数据 */
else
status = -EFAULT;
mutex_unlock(&spidev->buf_lock);
return status;
}
spidev_sync_write函数的具体实现如下：
static inline ssize_t
spidev_sync_write(struct spidev_data *spidev, size_t len)
{
struct spi_transfer t = {
.tx_buf = spidev->tx_buffer, /* 指定tx_buffer */
.len = len, /* 指定长度 */
.speed_hz = spidev->speed_hz, /* 指定传输速率 */
};
struct spi_message m;
spi_message_init(&m); /* spi消息初始化(初始化传输事务链表头) */
spi_message_add_tail(&t, &m); /* 添加spi传输到spi消息传输链表，将t放到message的尾部 */
return spidev_sync(spidev, &m); /* spi同步传输 */
}
上述代码中的spi_message_init函数，具体实现如下：
static inline void spi_message_init_no_memset(struct spi_message *m)
{
INIT_LIST_HEAD(&m->transfers);
INIT_LIST_HEAD(&m->resources);
}
static inline void spi_message_init(struct spi_message *m)
{
memset(m, 0, sizeof *m);
spi_message_init_no_memset(m);
}
通过源码可知，spi_message_init将传入的结构体spi_message全部内容初始化为0，并被初始化过的结构体spi_message传递给了函数spi_message_init_no_memset。
在spi_message_init_no_memset通过INIT_LIST_HEAD为m->transfers和m->resources分别创建双向链表的头节点。
在spidev_sync_write函数中，在完成SPI数据的链表的初始化之后又通过调用spi_message_add_tail函数，将struct spi_transfer t和struct spi_message m分别添加到前一步创建的双向链表的尾部。
在spidev_sync_write函数的最后通过调用spidev_sync函数进行SPI的同步传输，并将结果返回，此处spidev_sync函数的具体实现如下：
static ssize_t
spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
int status;
struct spi_device *spi;
spin_lock_irq(&spidev->spi_lock);
spi = spidev->spi;
spin_unlock_irq(&spidev->spi_lock);
if (spi == NULL)
status = -ESHUTDOWN;
else
status = spi_sync(spi, message);
if (status == 0)
status = message->actual_length;
return status;
}
梳理spidev_sync的数据传输流程：spidev_sync --> spi_sync --> __spi_sync --> __spi_queued_transfer --> kthread_queue_work最终将数据放到工作队列中，通过SPI总线驱动实现数据的发送功能。
spiev_read函数分析
spidev_read函数源码如下：
/* 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;
ssize_t status;
/* chipselect only toggles at start or end of operation */
if (count > bufsiz)
return -EMSGSIZE;
spidev = filp->private_data; /* 从私有数据中获取spidev_data数据 */
mutex_lock(&spidev->buf_lock); /* 加锁操作，数据安全 */
status = spidev_sync_read(spidev, count); /* 同步读取数据 */
if (status > 0) {
unsigned long missing;
missing = copy_to_user(buf, spidev->rx_buffer, status); /* 将读取的数据从内核态copy到用户态 */
if (missing == status)
status = -EFAULT;
else
status = status - missing;
}
mutex_unlock(&spidev->buf_lock); /* 解锁操作 */
return status;
}
spidev_sync_read函数的具体实现如下：
static inline ssize_t
spidev_sync_read(struct spidev_data *spidev, size_t len)
{
struct spi_transfer t = {
.rx_buf = spidev->rx_buffer, /* 指定rx_buffer */
.len = len,
.speed_hz = spidev->speed_hz,
};
struct spi_message m; /* 构造一个message */
spi_message_init(&m); /* 初始化spi_message */
spi_message_add_tail(&t, &m); /* 将transfer放到message的尾部 */
return spidev_sync(spidev, &m); /* 发起数据传输 */
}
将要发送的数据填充到struct spi_transfer t结构体中，跟spidev_sync_write同样的将通过spi_message_init函数初始化spi_message全部为0，通过spi_message_init_no_memset函数调用INIT_LIST_HEAD为m->transfers和m->resources分别创建双向链表的头节点。
与spidev_sync_write函数一样，在完成SPI数据的链表的初始化之后又通过调用spi_message_add_tail函数，将struct spi_transfer t和struct spi_message m分别添加到前一步创建的双向链表的尾部。
spidev_sync函数完成数据同步的流程此处不在重复。
spidev_ioctl函数分析
spidev_ioctl的源码如下：
static long
spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
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)
return -ENOTTY;
/* guard against device removal before, or while,
* we issue this ioctl.
*/
spidev = filp->private_data;
spin_lock_irq(&spidev->spi_lock);
spi = spi_dev_get(spidev->spi);
spin_unlock_irq(&spidev->spi_lock);
if (spi == NULL)
return -ESHUTDOWN;
/* use the buffer lock here for triple duty:
* - prevent I/O (from us) so calling spi_setup() is safe;
* - prevent concurrent SPI_IOC_WR_* from morphing
* data fields while SPI_IOC_RD_* reads them;
* - SPI_IOC_MESSAGE needs the buffer locked "normally".
*/
mutex_lock(&spidev->buf_lock);
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_MODE32:
retval = put_user(spi->mode & SPI_MODE_MASK,
(__u32 __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(spidev->speed_hz, (__u32 __user *)arg);
break;
/* write requests */
case SPI_IOC_WR_MODE:
case SPI_IOC_WR_MODE32:
if (cmd == SPI_IOC_WR_MODE)
retval = get_user(tmp, (u8 __user *)arg);
else
retval = get_user(tmp, (u32 __user *)arg);
if (retval == 0) {
struct spi_controller *ctlr = spi->controller;
u32 save = spi->mode;
if (tmp & ~SPI_MODE_MASK) {
retval = -EINVAL;
break;
}
if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
ctlr->cs_gpiods[spi->chip_select])
tmp |= SPI_CS_HIGH;
tmp |= spi->mode & ~SPI_MODE_MASK;
spi->mode = (u16)tmp;
retval = spi_setup(spi);
if (retval < 0)
spi->mode = save;
else
dev_dbg(&spi->dev, "spi mode %x\n", tmp);
}
break;
case SPI_IOC_WR_LSB_FIRST:
retval = get_user(tmp, (__u8 __user *)arg);
if (retval == 0) {
u32 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) {
spidev->speed_hz = tmp;
dev_dbg(&spi->dev, "%d Hz (max)\n",
spidev->speed_hz);
}
spi->max_speed_hz = save;
}
break;
default:
/* segmented and/or full-duplex I/O request */
/* Check message and copy into scratch area */
ioc = spidev_get_ioc_message(cmd,
(struct spi_ioc_transfer __user *)arg, &n_ioc);
if (IS_ERR(ioc)) {
retval = PTR_ERR(ioc);
break;
}
if (!ioc)
break; /* n_ioc is also 0 */
/* translate to spi_message, execute */
retval = spidev_message(spidev, ioc, n_ioc);
kfree(ioc);
break;
}
mutex_unlock(&spidev->buf_lock);
spi_dev_put(spi);
return retval;
}
spidev_compat_ioctl函数分析
spidev_open函数分析
spidev_open函数源码如下：
static int spidev_open(struct inode *inode, struct file *filp)
{
struct spidev_data *spidev;
int status = -ENXIO;
mutex_lock(&device_list_lock);
/* 在device_list链表中查找和inode下的注册此设备号一致的设备 */
list_for_each_entry(spidev, &device_list, device_entry) {
if (spidev->devt == inode->i_rdev) {
status = 0;
break;
}
}
if (status) {
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