内核版本:3.9.5
spi_master
struct spi_master用来描述一个SPI主控制器,我们一般不需要自己编写spi控制器驱动.
1 /*结构体master代表一个SPI接口,或者叫一个SPI主机控制器,一个接口对应一条SPI总线,master->bus_num则记录了这个总线号*/ 2 struct spi_master { 3 struct device dev; 4 5 struct list_head list; 6 7 /* other than negative (== assign one dynamically), bus_num is fully 8 * board-specific. usually that simplifies to being SOC-specific. 9 * example: one SOC has three SPI controllers, numbered 0..2, 10 * and one board's schematics might show it using SPI-2. software 11 * would normally use bus_num=2 for that controller. 12 */ 13 s16 bus_num;/*总线编号,从零开始.系统会用这个值去和系统中board_list链表中加入的每一个boardinfo结构 14 (每个boardinfo结构都是一个spi_board_info的集合,每一个spi_board_info都是对应一个SPI(从)设备的描述)中的每一个 15 spi_board_info中的bus_num进行匹配,如果匹配上就说明这个spi_board_info描述的SPI(从)设备是链接在此总线上的,因 16 此就会调用spi_new_device去创建一个spi_device*/ 17 18 /* chipselects will be integral to many controllers; some others 19 * might use board-specific GPIOs. 20 */ 21 u16 num_chipselect;//支持的片选的数量.从设备的片选号不能大于这个数.该值当然不能为0,否则会注册失败 22 23 /* some SPI controllers pose alignment requirements on DMAable 24 * buffers; let protocol drivers know about these requirements. 25 */ 26 u16 dma_alignment; 27 28 /* spi_device.mode flags understood by this controller driver */ 29 u16 mode_bits; 30 31 /* other constraints relevant to this driver */ 32 u16 flags; 33 #define SPI_MASTER_HALF_DUPLEX BIT(0) /* can't do full duplex */ 34 #define SPI_MASTER_NO_RX BIT(1) /* can't do buffer read */ 35 #define SPI_MASTER_NO_TX BIT(2) /* can't do buffer write */ 36 37 /* lock and mutex for SPI bus locking */ 38 spinlock_t bus_lock_spinlock; 39 struct mutex bus_lock_mutex; 40 41 /* flag indicating that the SPI bus is locked for exclusive use */ 42 bool bus_lock_flag; 43 44 /* Setup mode and clock, etc (spi driver may call many times). 45 * 46 * IMPORTANT: this may be called when transfers to another 47 * device are active. DO NOT UPDATE SHARED REGISTERS in ways 48 * which could break those transfers. 49 */ 50 int (*setup)(struct spi_device *spi);//根据spi设备更新硬件配置 51 52 /* bidirectional bulk transfers 53 * 54 * + The transfer() method may not sleep; its main role is 55 * just to add the message to the queue. 56 * + For now there's no remove-from-queue operation, or 57 * any other request management 58 * + To a given spi_device, message queueing is pure fifo 59 * 60 * + The master's main job is to process its message queue, 61 * selecting a chip then transferring data 62 * + If there are multiple spi_device children, the i/o queue 63 * arbitration algorithm is unspecified (round robin, fifo, 64 * priority, reservations, preemption, etc) 65 * 66 * + Chipselect stays active during the entire message 67 * (unless modified by spi_transfer.cs_change != 0). 68 * + The message transfers use clock and SPI mode parameters 69 * previously established by setup() for this device 70 */ 71 int (*transfer)(struct spi_device *spi, 72 struct spi_message *mesg);/*添加消息到队列的方法.此函数不可睡眠,其作用只是安排需要的传送,并且在适当的时候(传\ 73 送完成或者失败)调用spi_message中的complete方法,来将结果报告给用户*/ 74 75 /* called on release() to free memory provided by spi_master */ 76 void (*cleanup)(struct spi_device *spi);/*cleanup函数会在spidev_release函数中被调用,spidev_release被登记为spi dev的release 77 函数*/ 78 79 /* 80 * These hooks are for drivers that want to use the generic 81 * master transfer queueing mechanism. If these are used, the 82 * transfer() function above must NOT be specified by the driver. 83 * Over time we expect SPI drivers to be phased over to this API. 84 */ 85 bool queued; 86 struct kthread_worker kworker; 87 struct task_struct *kworker_task; 88 struct kthread_work pump_messages; 89 spinlock_t queue_lock; 90 struct list_head queue; 91 struct spi_message *cur_msg; 92 bool busy; 93 bool running; 94 bool rt; 95 96 int (*prepare_transfer_hardware)(struct spi_master *master); 97 int (*transfer_one_message)(struct spi_master *master, 98 struct spi_message *mesg); 99 int (*unprepare_transfer_hardware)(struct spi_master *master); 100 /* gpio chip select */ 101 int *cs_gpios; 102 };
spi控制器的驱动一般在arch/.../mach-*/board-*.c声明,注册一个平台设备,然后在driver/spi下面建立一个平台驱动.spi_master注册过程中会扫描arch/.../mach-*/board-*.c 中调用spi_register_board_info注册的信息,为每一个与本总线编号相同的信息建立一个spi_device.根据Linux内核的驱动模型,注册在同一总线下的驱动和设备会进行匹配.spi_bus_type总线匹配的依据是名字.这样当自己编写的spi_driver和spi_device同名的时候,spi_driver的probe方法就会被调用.spi_driver就能看到与自己匹配的spi_device了.
spi_device
struct spi_device用来描述一个SPI从设备.
1 /*该结构用于描述SPI设备,也就是从设备的相关信息. 2 NOTE:SPI子系统只支持主模式,也就是说SOC上的SPI只能工作在master模式,外围设备只能为slave模式*/ 3 struct spi_device { 4 struct device dev; 5 struct spi_master *master;//对应的控制器指针 6 u32 max_speed_hz;//spi传输时钟 7 u8 chip_select;//片选号,用来区分同一主控制器上的设备 8 u8 mode;//各bit的定义如下,主要是传输模式/片选极性 9 #define SPI_CPHA 0x01 /* clock phase */ 10 #define SPI_CPOL 0x02 /* clock polarity */ 11 #define SPI_MODE_0 (0|0) /* (original MicroWire) */ 12 #define SPI_MODE_1 (0|SPI_CPHA) 13 #define SPI_MODE_2 (SPI_CPOL|0) 14 #define SPI_MODE_3 (SPI_CPOL|SPI_CPHA) 15 #define SPI_CS_HIGH 0x04 /* chipselect active high? *//*片选电位为高*/ 16 #define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire *//*先输出低比特*/ 17 #define SPI_3WIRE 0x10 /* SI/SO signals shared *//*输入输出共享接口,此时只能做半双工*/ 18 #define SPI_LOOP 0x20 /* loopback mode *//*回写/回显模式*/ 19 #define SPI_NO_CS 0x40 /* 1 dev/bus, no chipselect */ 20 #define SPI_READY 0x80 /* slave pulls low to pause */ 21 u8 bits_per_word;/*每个字长的比特数*/ 22 int irq;/*使用到的中断号*/ 23 void *controller_state; 24 void *controller_data; 25 char modalias[SPI_NAME_SIZE];/*spi设备的名字*/ 26 int cs_gpio; /* chip select gpio */ 27 28 /* 29 * likely need more hooks for more protocol options affecting how 30 * the controller talks to each chip, like: 31 * - memory packing (12 bit samples into low bits, others zeroed) 32 * - priority 33 * - drop chipselect after each word 34 * - chipselect delays 35 * - ... 36 */ 37 };
spi_driver
struct spi_driver用于描述SPI(从)设备驱动.驱动核心将根据driver.name和spi_board_info的modalias进行匹配,如过modalia和name相等,则绑定驱动程序和arch/.../mach-xxx/board-xxx.c中调用spi_register_board_info注册的信息对应的spi_device设备.它的形式和struct platform_driver是一致的.
1 struct spi_driver { 2 const struct spi_device_id *id_table; 3 int (*probe)(struct spi_device *spi);/*和spi_device匹配成功之后会调用这个方法.因此这个方法需要对设备和私有数据进行初始化*/ 4 int (*remove)(struct spi_device *spi);/*解除spi_device和spi_driver的绑定,释放probe申请的资源*/ 5 void (*shutdown)(struct spi_device *spi);/*一般牵扯到电源管理会用到,关闭*/ 6 int (*suspend)(struct spi_device *spi, pm_message_t mesg);/*一般牵扯到电源管理会用到,挂起*/ 7 int (*resume)(struct spi_device *spi);/*一般牵扯到电源管理会用到,恢复*/ 8 struct device_driver driver; 9 };
spi_board_info
struct spi_board_info是板级信息,是在移植时就写好的,并且要将其注册.
1 /*该结构也是对SPI(从)设备(spi_device)的描述,只不过它是板级信息,最终该结构的所有字段都将用于初始化SPI设备结构体spi_device*/ 2 struct spi_board_info { 3 /* the device name and module name are coupled, like platform_bus; 4 * "modalias" is normally the driver name. 5 * 6 * platform_data goes to spi_device.dev.platform_data, 7 * controller_data goes to spi_device.controller_data, 8 * irq is copied too 9 */ 10 char modalias[SPI_NAME_SIZE];/*spi设备名,会拷贝到spi_device的相应字段中.这是设备spi_device在SPI总线spi_bus_type上匹配驱动的唯一标识*/ 11 const void *platform_data;/*平台数据*/ 12 void *controller_data; 13 int irq;/*中断号*/ 14 15 /* slower signaling on noisy or low voltage boards */ 16 u32 max_speed_hz;/*SPI设备工作时的波特率*/ 17 18 19 /* bus_num is board specific and matches the bus_num of some 20 * spi_master that will probably be registered later. 21 * 22 * chip_select reflects how this chip is wired to that master; 23 * it's less than num_chipselect. 24 */ 25 u16 bus_num;/*该SPI(从)设备所在总线的总线号,就记录了所属的spi_master之中的bus_num编号.一个spi_master就对应一条总线*/ 26 u16 chip_select;/*片选号.该SPI(从)设备在该条SPI总线上的设备号的唯一标识*/ 27 28 /* mode becomes spi_device.mode, and is essential for chips 29 * where the default of SPI_CS_HIGH = 0 is wrong. 30 */ 31 u8 mode;/*参考spi_device中的成员*/ 32 33 /* ... may need additional spi_device chip config data here. 34 * avoid stuff protocol drivers can set; but include stuff 35 * needed to behave without being bound to a driver: 36 * - quirks like clock rate mattering when not selected 37 */ 38 };
spi_transfer
struct spi_transfer是对一次完整的数据传输的描述.每个spi_transfer总是读取和写入同样长度的比特数,但是可以很容易的使用空指针舍弃读或写.为spi_transfer和spi_message分配的内存应该在消息处理期间保证是完整的.
1 struct spi_transfer { 2 /* it's ok if tx_buf == rx_buf (right?) 3 * for MicroWire, one buffer must be null 4 * buffers must work with dma_*map_single() calls, unless 5 * spi_message.is_dma_mapped reports a pre-existing mapping 6 */ 7 const void *tx_buf;/*发送缓冲区地址,这里存放要写入设备的数据(必须是dma_safe),或者为NULL*/ 8 void *rx_buf;/*接收缓冲区地址,从设备中读取的数据(必须是dma_safe)就放在这里,或者为NULL*/ 9 unsigned len;/*传输数据的长度.记录了tx和rx的大小(字节数),这里不是指它的和,而是各自的长度,他们总是相等的*/ 10 11 dma_addr_t tx_dma;/*如果spi_message.is_dma_mapped是真,这个是tx的dma地址*/ 12 dma_addr_t rx_dma;/*如果spi_message.is_dma_mapped是真,这个是rx的dma地址*/ 13 14 unsigned cs_change:1;/*影响此次传输之后的片选.指示本次transfer结束之后是否要重新片选并调用setup改变设置.若为1则表示当该transfer 15 传输完后,改变片选信号.这个标志可以减少系统开销*/ 16 u8 bits_per_word;/*每个字长的比特数.如果是0,使用默认值*/ 17 u16 delay_usecs;/*此次传输结束和片选改变之间的延时,之后就会启动另一个传输或者结束整个消息*/ 18 u32 speed_hz;/*通信时钟.如果是0,使用默认值*/ 19 20 struct list_head transfer_list;/*用来连接的双向链表节点,用于将该transfer链入message*/ 21 };
再说一下:cs_change影响此transfer完成后是否禁用片选线并调用setup改变配置.(这个标志量就是chip select change片选改变的意思).没有特殊情况,一个spi_message因该只在最后一个transfer置位该标志量.
spi_message
struct spi_message就是对多个spi_transfer的封装.spi_message用来原子的执行spi_transfer表示的一串数组传输请求.这个传输队列是原子的,这意味着在这个消息完成之前不会有其它消息占用总线.消息的执行总是按照FIFO的顺序.向底层提交spi_message的代码要负责管理它的内存空间.未显示初始化的内存需要使用0来初始化.为spi_transfer和spi_message分配的内存应该在消息处理期间保证是完整的.
1 struct spi_message { 2 struct list_head transfers;/*此次消息的传输段(spi_transfer)队列,一个消息可以包含多个传输段(spi_transfer)*/ 3 4 struct spi_device *spi;/*传输的目的设备,无论如何这里都是spi从设备,至于数据流向(是从主机到从设备还是从从设备到主机)这是由write/read 5 每个传输段(spi_transfer)内部的tx_buf或者是rx_buf决定的*/ 6 7 unsigned is_dma_mapped:1;/*如果为真,此次调用提供dma和cpu虚拟地址.spi主机提供了dma缓存池.如果此消息确定要使用dma(那当然更好 8 了).则从那个缓存池中申请高速缓存.替代传输段(spi_transfer)中的tx_buf/rx_buf*/ 9 10 /* REVISIT: we might want a flag affecting the behavior of the 11 * last transfer ... allowing things like "read 16 bit length L" 12 * immediately followed by "read L bytes". Basically imposing 13 * a specific message scheduling algorithm. 14 * 15 * Some controller drivers (message-at-a-time queue processing) 16 * could provide that as their default scheduling algorithm. But 17 * others (with multi-message pipelines) could need a flag to 18 * tell them about such special cases. 19 */ 20 21 /* completion is reported through a callback */ 22 void (*complete)(void *context);/*用于异步传输完成时调用的回调函数*/ 23 void *context;/*回调函数的参数*/ 24 unsigned actual_length;/*此次传输的实际长度,这个长度包括了此消息spi_message中所有传输段spi_transfer传输的长度之和(不管每个传 25 输段spi_transfer到底是输入还是输出,因为本来具体的传输就是针对每一个传输段spi_transfer来进行的)*/ 26 int status;/*执行的结果.成功被置0,否则是一个负的错误码*/ 27 28 /* for optional use by whatever driver currently owns the 29 * spi_message ... between calls to spi_async and then later 30 * complete(), that's the spi_master controller driver. 31 */ 32 /*下面两个成员是给拥有本消息的驱动选用的.spi_master会使用它们.自己最好不要使用*/ 33 struct list_head queue;/*用于将该message链入bitbang等待队列*/ 34 void *state; 35 };
spi_bitbang
struct spi_bitbang结构用于控制实际的数据传输.
1 struct spi_bitbang { 2 struct workqueue_struct *workqueue;/*工作队列*/ 3 struct work_struct work; 4 5 spinlock_t lock; 6 struct list_head queue; 7 u8 busy; 8 u8 use_dma; 9 u8 flags; /* extra spi->mode support */ 10 11 struct spi_master *master;/*bitbang所属的master*/ 12 13 /* setup_transfer() changes clock and/or wordsize to match settings 14 * for this transfer; zeroes restore defaults from spi_device. 15 */ 16 int (*setup_transfer)(struct spi_device *spi, 17 struct spi_transfer *t);/*用于设置设备传输时的时钟,字长等*/ 18 19 void (*chipselect)(struct spi_device *spi, int is_on); 20 #define BITBANG_CS_ACTIVE 1 /* normally nCS, active low */ 21 #define BITBANG_CS_INACTIVE 0 22 23 /* txrx_bufs() may handle dma mapping for transfers that don't 24 * already have one (transfer.{tx,rx}_dma is zero), or use PIO 25 */ 26 int (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t); 27 28 /* txrx_word[SPI_MODE_*]() just looks like a shift register */ 29 u32 (*txrx_word[4])(struct spi_device *spi, 30 unsigned nsecs, 31 u32 word, u8 bits); 32 };
本文引用:http://blog.csdn.net/yuanlulu/article/details/6318165