來自:http://blog.csdn.net/woshixingaaa/article/details/6574224
這篇文檔主要介紹spi數據傳輸過程。
當應用層要向設備傳輸數據的時候,會通過ioctl向設備驅動發送傳輸數據的命令。如圖,向SPI從設備發送讀寫命令,實際的讀寫操作還是調用了主機控制器驅動的數據傳輸函數。transfer函數用於spi的IO傳輸。但是,transfer函數一般不會執行真正的傳輸操作,而是把要傳輸的內容放到一個隊列裏,然後調用一種類似底半部的機制進行真正的傳輸。這是因爲,spi總線一般會連多個spi設備,而spi設備間的訪問可能會併發。如果直接在transfer函數中實現傳輸,那麼會產生競態,spi設備互相間會干擾。所以,真正的spi傳輸與具體的spi控制器的實現有關,spi的框架代碼中沒有涉及。像spi設備的片選,根據具體設備進行時鐘調整等等都在實現傳輸的代碼中被調用。spi的傳輸命令都是通過結構spi_message定義,設備程序調用transfer函數將spi_message交給spi總線驅動,總線驅動再將message傳到底半部排隊,實現串行化傳輸。
在spidev.c中實現了file_operations:
- <span style="font-size:18px;">static struct file_operations spidev_fops = {
- .owner = THIS_MODULE,
- .write = spidev_write,
- .read = spidev_read,
- .unlocked_ioctl = spidev_ioctl,
- .open = spidev_open,
- .release = spidev_release,
- };</span>
- <span style="font-size:18px;">static long
- spidev_ioctl(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;
- /*查看這個命令的幻數字段是否爲'k'*/
- if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)
- return -ENOTTY;
- /*如果方向是用戶空間從內核讀,即內核向用戶空間寫,則檢查用戶空間的地址是否有效*/
- if (_IOC_DIR(cmd) & _IOC_READ)
- err = !access_ok(VERIFY_WRITE,
- (void __user *)arg, _IOC_SIZE(cmd));
- /*如果方向是用戶空間向內核寫,即內核讀用戶空間,則檢查用戶空間的地址是否有效*/
- if (err == 0 && _IOC_DIR(cmd) & _IOC_WRITE)
- err = !access_ok(VERIFY_READ,
- (void __user *)arg, _IOC_SIZE(cmd));
- if (err)
- return -EFAULT;
- /* 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;
- mutex_lock(&spidev->buf_lock);
- switch (cmd) {
- /* read requests */
- case SPI_IOC_RD_MODE:
- /*因爲已經進行了地址是否有效的檢查,所以這裏使用__put_user,__get_user,__copy_from_user可以節省幾個時鐘週期呢*/
- 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;
- /*設置SPI模式*/
- case SPI_IOC_WR_MODE:
- retval = __get_user(tmp, (u8 __user *)arg);
- if (retval == 0) {
- /*先將之前的模式保存起來,一旦設置失敗進行回覆*/
- u8 save = spi->mode;
- 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) {
- retval = -ENOTTY;
- break;
- }
- /*得到用戶空間數據的大小*/
- tmp = _IOC_SIZE(cmd);
- /*如果這些數據不能分成spi_ioc_transfer的整數倍,則不能進行傳輸,spi_io_transfer是對spi_transfer的映射*/
- if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) {
- retval = -EINVAL;
- break;
- }
- /*計算出能分多少個spi_ioc_transfer*/
- n_ioc = tmp / sizeof(struct spi_ioc_transfer);
- if (n_ioc == 0)
- break;
- /*在內核中分配裝載這些數據的內存空間*/
- ioc = kmalloc(tmp, GFP_KERNEL);
- if (!ioc) {
- retval = -ENOMEM;
- break;
- }
- /*把用戶空間的數據拷貝過來*/
- if (__copy_from_user(ioc, (void __user *)arg, tmp)) {
- kfree(ioc);
- retval = -EFAULT;
- break;
- }
- /*進行數據傳輸*/
- <span style="color:#ff0000;">retval = spidev_message(spidev, ioc, n_ioc);</span>
- kfree(ioc);
- break;
- }
- mutex_unlock(&spidev->buf_lock);
- spi_dev_put(spi);
- return retval;
- }
- </span>
下面跟蹤spidev_message看看:
- <span style="font-size:18px;">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;
- unsigned n, total;
- u8 *buf;
- int status = -EFAULT;
- /*初始化spi_message的tranfers鏈表頭*/
- spi_message_init(&msg);
- /*分配n個spi_transfer的內存空間,一個spi_message由多個數據段spi_message組成*/
- k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);
- if (k_xfers == NULL)
- return -ENOMEM;
- buf = spidev->buffer;
- total = 0;
- /*這個for循環的主要任務是將所有的spi_transfer組裝成一個spi_message*/
- for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
- n;
- n--, k_tmp++, u_tmp++) {
- /*u_tmp是從用戶空間傳下來的spi_ioc_message的大小,spi_ioc_message是對spi_message的映射*/
- k_tmp->len = u_tmp->len;
- /*統計要傳輸數據的總量*/
- total += k_tmp->len;
- if (total > bufsiz) {
- status = -EMSGSIZE;
- goto done;
- }
- /*spi_transfer是一個讀寫的buffer對,如果是要接收則把buffer給接收的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;
- }
- /*如果要傳輸,這個buffer給tx_buf使用,從用戶空間拷過來要傳輸的數據*/
- if (u_tmp->tx_buf) {
- k_tmp->tx_buf = buf;
- if (copy_from_user(buf, (const u8 __user *)
- (uintptr_t) u_tmp->tx_buf,
- u_tmp->len))
- goto done;
- }
- /*指向下一段內存*/
- buf += k_tmp->len;
- /*最後一個transfer傳輸完畢是否會影響片選*/
- k_tmp->cs_change = !!u_tmp->cs_change;
- /*每字長的字節數*/
- k_tmp->bits_per_word = u_tmp->bits_per_word;
- /*一段數據傳輸完需要一定的時間等待*/
- k_tmp->delay_usecs = u_tmp->delay_usecs;
- /*初始化傳輸速度*/
- k_tmp->speed_hz = u_tmp->speed_hz;
- /*將spi_transfer通過它的transfer_list字段掛到spi_message的transfer隊列上*/
- spi_message_add_tail(k_tmp, &msg);
- }
- /*調用底層的傳輸函數*/
- <span style="color:#ff0000;">status = spidev_sync(spidev, &msg);</span>
- if (status < 0)
- goto done;
- /* copy any rx data out of bounce buffer */
- buf = spidev->buffer;
- /*把傳輸數據拷貝到用戶空間打印出來,可以查看是否傳輸成功*/
- for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
- 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:
- kfree(k_xfers);
- return status;
- }
- </span>
看spidev_sync的實現:
- <span style="font-size:18px;">static ssize_t
- spidev_sync(struct spidev_data *spidev, struct spi_message *message)
- {
- /*聲明並初始化一個完成量*/
- DECLARE_COMPLETION_ONSTACK(done);
- int status;
- /*指定spi_message使用的喚醒完成量函數*/
- message->complete = spidev_complete;
- message->context = &done;
- spin_lock_irq(&spidev->spi_lock);
- if (spidev->spi == NULL)
- status = -ESHUTDOWN;
- else
- /*調用spi核心中的函數進行數據傳輸*/
- <span style="color:#ff0000;"> status = spi_async(spidev->spi, message);</span>
- spin_unlock_irq(&spidev->spi_lock);
- if (status == 0) {
- /*等待完成量被喚醒*/
- wait_for_completion(&done);
- status = message->status;
- if (status == 0)
- status = message->actual_length;
- }
- return status;
- }
- </span>
- <span style="font-size:18px;">static inline int
- spi_async(struct spi_device *spi, struct spi_message *message)
- {
- message->spi = spi;
- return spi->master->transfer(spi, message);
- }
- </span>
bitbang->master->transfer= spi_bitbang_transfer;
看spi_bitbang_transfer的實現:
- <span style="font-size:18px;">int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m)
- {
- struct spi_bitbang *bitbang;
- unsigned long flags;
- int status = 0;
- m->actual_length = 0;
- m->status = -EINPROGRESS;
- /*在spi_alloc_master函數中調用spi_master_set_devdata把struct s3c24xx_spi結構存放起來,而struct spi_bitbang正是struct s3c24xx_spi結構所包含的第一個結構*/
- bitbang = spi_master_get_devdata(spi->master);
- spin_lock_irqsave(&bitbang->lock, flags);
- if (!spi->max_speed_hz)
- status = -ENETDOWN;
- else {
- /*把message加入到bitbang的等待隊列中*/
- list_add_tail(&m->queue, &bitbang->queue);
- /*把bitbang-work加入bitbang->workqueue中,調度運行*/
- queue_work(bitbang->workqueue, &bitbang->work);
- }
- spin_unlock_irqrestore(&bitbang->lock, flags);
- return status;
- }
- EXPORT_SYMBOL_GPL(spi_bitbang_transfer);
- </span>
分析工作隊列的處理函數:
- <span style="font-size:18px;">static void bitbang_work(struct work_struct *work)
- {
- struct spi_bitbang *bitbang =
- container_of(work, struct spi_bitbang, work);
- unsigned long flags;
- spin_lock_irqsave(&bitbang->lock, flags);
- /*設置成忙狀態*/
- bitbang->busy = 1;
- /*對bitqueue中的每一個spi_message進行處理*/
- while (!list_empty(&bitbang->queue)) {
- struct spi_message *m;
- struct spi_device *spi;
- unsigned nsecs;
- struct spi_transfer *t = NULL;
- unsigned tmp;
- unsigned cs_change;
- int status;
- int (*setup_transfer)(struct spi_device *,
- struct spi_transfer *);
- m = container_of(bitbang->queue.next, struct spi_message,
- queue);
- /*從隊列中驅動這個spi_message*/
- list_del_init(&m->queue);
- spin_unlock_irqrestore(&bitbang->lock, flags);
- nsecs = 100;
- spi = m->spi;
- tmp = 0;
- cs_change = 1;
- status = 0;
- setup_transfer = NULL;
- /*對spi_message的transfers上的每個spi_transfer進行處理*/
- list_for_each_entry (t, &m->transfers, transfer_list) {
- 。。。。。。。。。。。。。。。。。
- if (t->len) {
- if (!m->is_dma_mapped)
- t->rx_dma = t->tx_dma = 0;
- /*調用bitbang->txrx_bufs進行數據的傳輸,bitbang->txrx_bufs = s3c24xx_spi_txrx;這個在s3c24xx_spi_probe中進行賦值的*/
- <span style="color:#ff0000;">status = bitbang->txrx_bufs(spi, t);</span>
- }
- 。。。。。。。。。。。。。。。。
- m->status = status;
- /*傳輸完成,喚醒剛纔的那個完成變量*/
- m->complete(m->context);
- /* restore speed and wordsize */
- if (setup_transfer)
- setup_transfer(spi, NULL);
- if (!(status == 0 && cs_change)) {
- ndelay(nsecs);
- bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
- ndelay(nsecs);
- }
- spin_lock_irqsave(&bitbang->lock, flags);
- }
- bitbang->busy = 0;
- spin_unlock_irqrestore(&bitbang->lock, flags);
- }
- </span>
- <span style="font-size:18px;">static int s3c24xx_spi_txrx(struct spi_device *spi, struct spi_transfer *t)
- {
- struct s3c24xx_spi *hw = to_hw(spi);
- dev_dbg(&spi->dev, "txrx: tx %p, rx %p, len %d\n",
- t->tx_buf, t->rx_buf, t->len);
- hw->tx = t->tx_buf; //發送指針
- hw->rx = t->rx_buf; //接收指針
- hw->len = t->len; //需要發送/接收的數目
- hw->count = 0; //存放實際spi傳輸的數據數目
- /*初始化了完成量*/
- init_completion(&hw->done);
- /*
- *只需發送第一個字節(如果發送爲空,則發送0xff),中斷中就會自動發送完其他字節(並接受數據)
- *直到所有數據發送完畢且所有數據接收完畢才返回
- */
- writeb(hw_txbyte(hw, 0), hw->regs + S3C2410_SPTDAT);
- /*等待完成量被喚醒*/
- wait_for_completion(&hw->done);
- return hw->count;
- }
- static inline unsigned int hw_txbyte(struct s3c24xx_spi *hw, int count)
- {
- return hw->tx ? hw->tx[count] : 0xff;
- //如果還有數據沒接收完且要發送的數據經已發送完畢,發送空數據0xFF
- }
- </span>
- <span style="font-size:18px;">static irqreturn_t s3c24xx_spi_irq(int irq, void *dev)
- {
- struct s3c24xx_spi *hw = dev;
- /*讀取spi的狀態寄存器*/
- unsigned int spsta = readb(hw->regs + S3C2410_SPSTA);
- unsigned int count = hw->count;
- /*檢測衝突*/
- if (spsta & S3C2410_SPSTA_DCOL) {
- dev_dbg(hw->dev, "data-collision\n");
- /*喚醒完成量*/
- complete(&hw->done);
- goto irq_done;
- }
- /*設備忙*/
- if (!(spsta & S3C2410_SPSTA_READY)) {
- dev_dbg(hw->dev, "spi not ready for tx?\n");
- /*喚醒完成量*/
- complete(&hw->done);
- goto irq_done;
- }
- hw->count++;
- /*接收數據*/
- if (hw->rx)
- hw->rx[count] = readb(hw->regs + S3C2410_SPRDAT);
- count++;
- /*如果count小於需要發送或接收數據的數目,發送其他數據*/
- if (count < hw->len)
- writeb(hw_txbyte(hw, count), hw->regs + S3C2410_SPTDAT);
- else
- /*喚醒完成量,通知s3c24xx_spi_txrx函數*/
- complete(&hw->done);
- irq_done:
- return IRQ_HANDLED;
- }
- </span>