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linux中spi驱动框架

2016年09月14日 15:57:06 andylauren 阅读数：403

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linux下的SPI总线驱动在driver/spi目录中。

SPI驱动分为三层

SPI核心层 drivers/spi/spi.c 与平台无关

SPI控制器驱动层

SPI设备驱动层

每层的主要结构体和函数

SPI控制器驱动层（include/linux/spi/spi.h）

struct spi_master {struct device dev;s16 bus_num;//控制器对应的SPI总线号u16 num_chipselect;//支持片选数量int (* setup) (struct spi_device *spi);//SPI模式设备，在spi_add_device中调用int (* transfer) (struct spi_device *spi,struct spi_message *mesg);//读写方法的函数，可能会睡眠void (* cleanup) (struct spi_device *spi);//注销时候调用
};

SPI设备驱动层

spi_device对应某个特定的slave

struct spi_driver {int (* probe) (struct spi_device *spi);//匹配时调用，完成spi_transfer,spi_message,spi_message_init,spi_meassage_add_tail,spi_sync,spi_write_then_read的调用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;
};

struct spi_device {struct device dev;struct spi_master * master;u32 max_speed_hz;u8 chip_select;u8 mode;
#define SPI_CPHA    0x01
#define SPI_CPOL    0x02
#define SPI_MODE_0  (0|0)
#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
#define SPI_LSB_FIRST   0x08
#define SPI_3WIRE   0x10
#define SPI_LOOP    0x20u8 bits_per_word;int irq;void * controller_state;void * controller_data;const char * modalias;
};

struct spi_transfer {const void * tx_buf;void * rx_buf;unsigned len;dma_addr_t tx_dma;dma_addr_t rx_dma;unsigned cs_change:1;u8 bits_per_word;u16 delay_usecs;u32 speed_hz;struct list_head transfer_list;
};

int spi_register_driver (    struct spi_driver *     sdrv);

struct spi_message {struct list_head transfers;struct spi_device * spi;unsigned is_dma_mapped:1;void (* complete) (void *context);void * context;unsigned actual_length;int status;struct list_head queue;void * state;
};

在每次使用spi_message可以使用函数：
void spi_message_init(structspi_message *m);
来初始化。
向spi_message添加transfers可以使用spi_message_add_tail()函数：
void spi_message_add_tail(structspi_transfer *t, struct spi_message *m);
一旦你准备好了spi_message，就可以使用spi_async()来向SPI系统提交了：
int spi_async(struct spi_device *spi,struct spi_message *message);
因为是异步的，一提交就立马返回了，这也就是说需要同步机制（complete就是了）。他确保不会睡眠，可安全的在中断handler或其他不可休眠的代码中调用。稍后会念念他的好的。
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。
使用完成回调机制稍显复杂，可以使用SPI系统提供的另一个同步版本：spi_sync():
int spi_sync(struct spi_device *spi,struct spi_message *message);
因为是同步的，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()在drivers/spi/spi.c中实现，其调用了spi_async()，并休眠直至complete返回。

spi_device的板信息用spi_board_info来描述，在init函数调用时会初始化。

struct spi_board_info {char modalias[KOBJ_NAME_LEN];const void * platform_data;void * controller_data;int irq;u32 max_speed_hz;u16 bus_num;u16 chip_select;u8 mode;
};

int __init spi_register_board_info ( struct spi_board_info const *   info,unsigned   n);

会把spi_board_info注册到链表board_list上。

之后，spi_master注册会调用scan_board_info扫描board_list找到挂接在它上面的spi设备。

然后创建并注册spi_device.

一个结构体spi_board_info对应着一个SPI设备spi_device

struct boardinfo{struct list_head list;struct spi_board_info board_info;
}
static LIST_HEAD(board_list);
static LIST_HEAD(spi_master_list);//初始化一个空链表

#define LIST_HEAD(name)

struct list_head name=LIST_HEAD_INIT(name)

#define LIST_HEAD_INIT(name) {&(name),&(name)}

struct list_head {struct list_head* next,*prev;};

struct device_driver结构体被定义在/include/linux/device.h，原型是：

struct device_driver {const char        *name;struct bus_type        *bus;

<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">module</span>        *<span class="hljs-title">owner</span>;</span>
<span class="hljs-keyword">const</span> <span class="hljs-keyword">char</span>        *mod_name;    <span class="hljs-comment">/* used for built-in modules */</span><span class="hljs-keyword">bool</span> suppress_bind_attrs;    <span class="hljs-comment">/* disables bind/unbind via sysfs */</span><span class="hljs-keyword">int</span> (*probe) (struct device *dev);
<span class="hljs-keyword">int</span> (*remove) (struct device *dev);
<span class="hljs-keyword">void</span> (*shutdown) (struct device *dev);
<span class="hljs-keyword">int</span> (*suspend) (struct device *dev, <span class="hljs-keyword">pm_message_t</span> state);
<span class="hljs-keyword">int</span> (*resume) (struct device *dev);
<span class="hljs-keyword">const</span> <span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">attribute_group</span> **<span class="hljs-title">groups</span>;</span><span class="hljs-keyword">const</span> <span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">dev_pm_ops</span> *<span class="hljs-title">pm</span>;</span><span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">driver_private</span> *<span class="hljs-title">p</span>;</span>

};

举例SPI驱动

spi_device设备

spi_board_info

init入口调用，spi_register_board_info(S3C_SPI_devs,ARRAY_SIZE(S3C_SPI_devs));

会把spi_board_info注册到board_list链表上。

之后会创建并注册spi_device

spi_driver驱动

1、声明并设置spi_driver结构体

2、注册spi_register_driver(&spi_driver);

3、实现probe操作，spi_transfer,spi_message的构建

spi_message_init,spi_message_add_tail,spi_sync调用

3.1、定义并设置 spi_transfer结构体

3.2、定义spi_message结构体

3.3、初始化meg，spi_message_init(&meg);

3.4、将st放入message队列spi_message_add_tail(&st,&meg);

3.5、将message与spi_device关联，发送meg，spi_sync(spi_device,&meg);