spi 驱动工作流程

驱动位于内核目录下 device/spi/spidev.c

整个spi驱动的工作流程如下

应用层调用设备驱动文件   spidev_ioctl函数

spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

        spidev_message(spidev, ioc, n_ioc);

               spidev_sync(spidev, &msg);

                    status = spi_async(spidev->spi, message);//将msg加入传输队列，同时调度工作队列handle函数处理msg队列

                              wait_for_completion(&done);//等待异步传输成功（异步又工作队列handle函数处理spi底层） 

//异步传输函数spi_async

int spi_async(struct spi_device *spi, struct spi_message *message)

{

 struct spi_master *master = spi->master;

 /* Half-duplex links include original MicroWire, and ones with

  * only one data pin like SPI_3WIRE (switches direction) or where

  * either MOSI or MISO is missing.  They can also be caused by

  * software limitations.

  */

 if ((master->flags & SPI_MASTER_HALF_DUPLEX)

   || (spi->mode & SPI_3WIRE)) {

  struct spi_transfer *xfer;

  unsigned flags = master->flags;

  list_for_each_entry(xfer, &message->transfers, transfer_list) {

   if (xfer->rx_buf && xfer->tx_buf)

    return -EINVAL;

   if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)

    return -EINVAL;

   if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)

    return -EINVAL;

  }

 }

 message->spi = spi;

 message->status = -EINPROGRESS;

 return master->transfer(spi, message);//在transfer函数中会发出工作队列调度命令

}

// master->transfer函数指针指向的s3c64xx_spi_transfer函数

static int s3c64xx_spi_transfer(struct spi_device *spi,

      struct spi_message *msg)

{

 struct s3c64xx_spi_driver_data *sdd;

 unsigned long flags;

 sdd = spi_master_get_devdata(spi->master);

 spin_lock_irqsave(&sdd->lock, flags);

 if (sdd->state & SUSPND) {

  spin_unlock_irqrestore(&sdd->lock, flags);

  return -ESHUTDOWN;

 }

 msg->status = -EINPROGRESS;

 msg->actual_length = 0;

 list_add_tail(&msg->queue, &sdd->queue);//添加msg到待处理队列上

 queue_work(sdd->workqueue, &sdd->work);//发出工作队列调度处理命令

 spin_unlock_irqrestore(&sdd->lock, flags);

 return 0;

}

//工作队列处理函数（被调度函数)

static void s3c64xx_spi_work(struct work_struct *work)

{

 struct s3c64xx_spi_driver_data *sdd = container_of(work,

     struct s3c64xx_spi_driver_data, work);

 unsigned long flags;

 /* Acquire DMA channels */

 while (!acquire_dma(sdd))

  msleep(10);

 spin_lock_irqsave(&sdd->lock, flags);

 while (!list_empty(&sdd->queue)

    && !(sdd->state & SUSPND)) {

  struct spi_message *msg;

  msg = container_of(sdd->queue.next, struct spi_message, queue);//从队列取msg

  list_del_init(&msg->queue);//删除队列上取出的msg单元

  /* Set Xfer busy flag */

  sdd->state |= SPIBUSY;

  spin_unlock_irqrestore(&sdd->lock, flags);

  handle_msg(sdd, msg);//spi底层发送接收处理函数    里面处理完会唤醒 msg->complete(msg->context);前面的休眠操作同步，具体可以到该函数里面去看

  spin_lock_irqsave(&sdd->lock, flags);

  sdd->state &= ~SPIBUSY;

 }

 spin_unlock_irqrestore(&sdd->lock, flags);

 /* Free DMA channels */

 s3c2410_dma_free(sdd->tx_dmach, &s3c64xx_spi_dma_client);

 s3c2410_dma_free(sdd->rx_dmach, &s3c64xx_spi_dma_client);

}

//异步处理的流程

s3c64xx_spi_transfer

            queue_work

                   s3c64xx_spi_work

                             handle_msg

                                            msg->complete //唤醒同步前面等待

        整个驱动对 工作队列 ，wait_for_completion等内核api做了比较好的运用，可以好好的学习下