Linux驱动分析之SPI驱动架构

Posted 2021-12-08 嵌入式软件开发交流

SPI体系结构

主要由三部分组成：

(1) SPI核心

(2) SPI控制器驱动

(3) SPI设备驱动

基本和I2C的架构差不多

重要结构体

内核版本：3.7.6

• spi_master
  

//SPI控制器
struct spi_master {
  struct device  dev;


  struct list_head list; //控制器链表


   //控制器对应的SPI总线号 SPI-2 对应bus_num= 2
  s16      bus_num;
  u16      num_chipselect;//控制器支持的片选数量，即能支持多少个spi设备 
  u16      dma_alignment;//DMA缓冲区对齐方式
  u16      mode_bits;// mode标志


  /* other constraints relevant to this driver */
  u16      flags;
#define SPI_MASTER_HALF_DUPLEX  BIT(0)  /* cant do full duplex */
#define SPI_MASTER_NO_RX  BIT(1)    /* cant do buffer read */
#define SPI_MASTER_NO_TX  BIT(2)    /* cant do buffer write */


  // 并发同步时使用
  spinlock_t    bus_lock_spinlock;
  struct mutex    bus_lock_mutex;


  /* flag indicating that the SPI bus is locked for exclusive use */
  bool      bus_lock_flag;


    //设置SPI mode和时钟， 在spi_add_device中调用
  int      (*setup)(struct spi_device *spi);
    //传输数据函数, 实现数据的双向传输
  int      (*transfer)(struct spi_device *spi,
            struct spi_message *mesg);
  //注销时回调
  void      (*cleanup)(struct spi_device *spi);


  /*
   * These hooks are for drivers that want to use the generic
   * master transfer queueing mechanism. If these are used, the
   * transfer() function above must NOT be specified by the driver.
   * Over time we expect SPI drivers to be phased over to this API.
   */
  bool        queued;
  struct kthread_worker    kworker;
  struct task_struct    *kworker_task;
  struct kthread_work    pump_messages;
  spinlock_t      queue_lock;
  struct list_head    queue;
  struct spi_message    *cur_msg;
  bool        busy;
  bool        running;
  bool        rt;


  int (*prepare_transfer_hardware)(struct spi_master *master);
  int (*transfer_one_message)(struct spi_master *master,
            struct spi_message *mesg);
  int (*unprepare_transfer_hardware)(struct spi_master *master);
}

• spi_driver
  

//SPI驱动，和platform_driver,i2c_driver类似
struct spi_driver {
  const struct spi_device_id *id_table;
  int  (*probe)(struct spi_device *spi);
  int  (*remove)(struct spi_device *spi);
  void  (*shutdown)(struct spi_device *spi);
  int  (*suspend)(struct spi_device *spi, pm_message_t mesg);
  int  (*resume)(struct spi_device *spi);
  struct device_driver  driver;
};

• spi_device
  

//SPI 设备
struct spi_device {
  struct device    dev;
  struct spi_master  *master; //指向SPI控制器
  u32      max_speed_hz; //最大速率
  u8      chip_select; //片选
  u8      mode; //SPI设备模式，使用下面的宏
#define  SPI_CPHA  0x01      /* clock phase */
#define  SPI_CPOL  0x02      /* clock polarity */
#define  SPI_MODE_0  (0|0)      /* (original MicroWire) */
#define  SPI_MODE_1  (0|SPI_CPHA)
#define  SPI_MODE_2  (SPI_CPOL|0)
#define  SPI_MODE_3  (SPI_CPOL|SPI_CPHA)
#define  SPI_CS_HIGH  0x04      /* chipselect active high? */
#define  SPI_LSB_FIRST  0x08      /* per-word bits-on-wire */
#define  SPI_3WIRE  0x10      /* SI/SO signals shared */
#define  SPI_LOOP  0x20      /* loopback mode */
#define  SPI_NO_CS  0x40      /* 1 dev/bus, no chipselect */
#define  SPI_READY  0x80      /* slave pulls low to pause */
  u8      bits_per_word;
  int      irq;
  void      *controller_state; //控制器运行状态
  void      *controller_data; //特定板子为控制器定义的数据
  char      modalias[SPI_NAME_SIZE];


};

• spi_message
  

//SPI传输数据结构体
struct spi_message {
  struct list_head  transfers; // spi_transfer链表头


  struct spi_device  *spi; //spi设备


  unsigned    is_dma_mapped:1;


  //发送完成回调
  void      (*complete)(void *context);
  void      *context;
  unsigned    actual_length;
  int      status;


  /* for optional use by whatever driver currently owns the
   * spi_message ...  between calls to spi_async and then later
   * complete(), thats the spi_master controller driver.
   */
  struct list_head  queue;
  void      *state;
};

• spi_transfer
  

// 该结构体是spi_message下的子单元，
struct spi_transfer {

  const void  *tx_buf;// 发送的数据缓存区
  void    *rx_buf;// 接收的数据缓存区
  unsigned  len;


  dma_addr_t  tx_dma; //tx_buf的DMA地址
  dma_addr_t  rx_dma; //rx_buf的DMA地址


  unsigned  cs_change:1;
  u8    bits_per_word;
  u16    delay_usecs;
  u32    speed_hz;


  struct list_head transfer_list;
};

总结上面结构体关系：

1. spi_driver和spi_device

spi_driver对应一套驱动方法，包含probe,remove等方法。spi_device对应真实的物理设备，每个spi设备都需要一个spi_device来描述。spi_driver与spi_device是一对多的关系，一个spi_driver上可以支持多个同类型的spi_device。

2. spi_master和spi_device

spi_master 与 spi_device 的关系和硬件上控制器与设备的关系一致，即spi_device依附于spi_master。

3. spi_message和spi_transfer

spi传输数据是以 spi_message 为单位的，我们需要传输的内容在 spi_transfer 中。spi_transfer是spi_message的子单元。

1 . 将本次需要传输的 spi_transfer 以 spi_transfer->transfer_list 为链表项，连接成一个transfer_list链表，挂接在本次传输的spi_message spi_message->transfers链表下。

2 . 将所有等待传输的 spi_message 以 spi_message->queue 为链表项，连接成个链表挂接在queue下。

API函数

//分配一个spi_master
struct spi_master *spi_alloc_master(struct device *dev, unsigned size)


//注册和注销spi_master
int spi_register_master(struct spi_master *master)
void spi_unregister_master(struct spi_master *master)


//注册和注销spi_driver
int spi_register_driver(struct spi_driver *sdrv)
void spi_unregister_driver(struct spi_driver *sdrv)


//初始化spi_message
void spi_message_init(struct spi_message *m)
//向spi_message添加transfers
void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)
//异步发送spi_message
int spi_async(struct spi_device *spi, struct spi_message *message)
//同步发送spi_message
int spi_sync(struct spi_device *spi, struct spi_message *message)


//spi同步写(封装了上面的函数)
int spi_write(struct spi_device *spi, const void *buf, size_t len)
//spi同步读(封装了上面的函数)
int spi_read(struct spi_device *spi, void *buf, size_t len)
//同步写并读取(封装了上面的函数)
int spi_write_then_read(struct spi_device *spi,
    const void *txbuf, unsigned n_tx,
    void *rxbuf, unsigned n_rx)

使用spi_async()需要注意的是，在complete未返回前不要轻易访问你一提交的spi_transfer中的buffer。也不能释放SPI系统正在使用的buffer。一旦你的complete返回了，这些buffer就又是你的了。

spi_sync是同步的，spi_sync提交完spi_message后不会立即返回，会一直等待其被处理。一旦返回就可以重新使用buffer了。spi_sync()调用了spi_async()，并休眠直至complete返回。

上面的传输函数最终都是调用spi_master的transfer()函数。

总结

SPI的架构和之前的I2C的结构基本差不多，我们会发现其实驱动中大量的结构体都是对参数和数据的封装。站在宏观的角度看，就是填充结构体，调用函数注册或发送。

上面是对Linux中SPI相关架构的分析，后面依然会拿出一些相对应的驱动来进行具体分析。希望能做到理论和实践相结合！