SPI子系统分析之二:数据结构

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.

/*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*/
struct spi_master {
struct device    dev;

struct list_head list;

/* other than negative (== assign one dynamically), bus_num is fully
* board-specific.  usually that simplifies to being SOC-specific.
* example:  one SOC has three SPI controllers, numbered 0..2,
* and one board's schematics might show it using SPI-2.  software
* would normally use bus_num=2 for that controller.
*/
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
(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
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
此就会调用spi_new_device去创建一个spi_device*/

/* chipselects will be integral to many controllers; some others
* might use board-specific GPIOs.
*/
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

/* some SPI controllers pose alignment requirements on DMAable
* buffers; let protocol drivers know about these requirements.
*/
u16            dma_alignment;

/* spi_device.mode flags understood by this controller driver */
u16            mode_bits;

/* other constraints relevant to this driver */
u16            flags;
#define SPI_MASTER_HALF_DUPLEX    BIT(0)        /* can't do full duplex */
#define SPI_MASTER_NO_RX    BIT(1)        /* can't do buffer read */
#define SPI_MASTER_NO_TX    BIT(2)        /* can't do buffer write */

/* lock and mutex for SPI bus locking */
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;

/* Setup mode and clock, etc (spi driver may call many times).
*
* IMPORTANT:  this may be called when transfers to another
* device are active.  DO NOT UPDATE SHARED REGISTERS in ways
* which could break those transfers.
*/
int            (*setup)(struct spi_device *spi);//根据spi设备更新硬件配置

/* bidirectional bulk transfers
*
* + The transfer() method may not sleep; its main role is
*   just to add the message to the queue.
* + For now there's no remove-from-queue operation, or
*   any other request management
* + To a given spi_device, message queueing is pure fifo
*
* + The master's main job is to process its message queue,
*   selecting a chip then transferring data
* + If there are multiple spi_device children, the i/o queue
*   arbitration algorithm is unspecified (round robin, fifo,
*   priority, reservations, preemption, etc)
*
* + Chipselect stays active during the entire message
*   (unless modified by spi_transfer.cs_change != 0).
* + The message transfers use clock and SPI mode parameters
*   previously established by setup() for this device
*/
int            (*transfer)(struct spi_device *spi,
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\
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*/

/* called on release() to free memory provided by spi_master */
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
函数*/

/*
* 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);
/* gpio chip select */
int            *cs_gpios;
};

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.

/*该结构用于描述SPI设备,也就是从设备的相关信息.
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*/
struct spi_device {
struct device        dev;
struct spi_master    *master;//对应的控制器指针
u32            max_speed_hz;//spi传输时钟
u8            chip_select;//片选号,用来区分同一主控制器上的设备
u8            mode;//各bit的定义如下,主要是传输模式/片选极性
#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? *//*片选电位为高*/
#define    SPI_LSB_FIRST    0x08            /* per-word bits-on-wire *//*先输出低比特*/
#define    SPI_3WIRE    0x10            /* SI/SO signals shared *//*输入输出共享接口,此时只能做半双工*/
#define    SPI_LOOP    0x20            /* loopback mode *//*回写/回显模式*/
#define    SPI_NO_CS    0x40            /* 1 dev/bus, no chipselect */
#define    SPI_READY    0x80            /* slave pulls low to pause */
u8            bits_per_word;/*每个字长的比特数*/
int            irq;/*使用到的中断号*/
void            *controller_state;
void            *controller_data;
char            modalias[SPI_NAME_SIZE];/*spi设备的名字*/
int            cs_gpio;    /* chip select gpio */

/*
* likely need more hooks for more protocol options affecting how
* the controller talks to each chip, like:
*  - memory packing (12 bit samples into low bits, others zeroed)
*  - priority
*  - drop chipselect after each word
*  - chipselect delays
*  - ...
*/
};

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.

struct spi_driver {
const struct spi_device_id *id_table;
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*/
int            (*remove)(struct spi_device *spi);/*解除spi_device和spi_driver的绑定,释放probe申请的资源*/
void            (*shutdown)(struct spi_device *spi);/*一般牵扯到电源管理会用到,关闭*/
int            (*suspend)(struct spi_device *spi, pm_message_t mesg);/*一般牵扯到电源管理会用到,挂起*/
int            (*resume)(struct spi_device *spi);/*一般牵扯到电源管理会用到,恢复*/
struct device_driver    driver;
};

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.

/*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*/
struct spi_board_info {
/* the device name and module name are coupled, like platform_bus;
* "modalias" is normally the driver name.
*
* platform_data goes to spi_device.dev.platform_data,
* controller_data goes to spi_device.controller_data,
* irq is copied too
*/
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*/
const void    *platform_data;/*平台数据*/
void        *controller_data;
int        irq;/*中断号*/

/* slower signaling on noisy or low voltage boards */
u32        max_speed_hz;/*SPI设备工作时的波特率*/

/* bus_num is board specific and matches the bus_num of some
* spi_master that will probably be registered later.
*
* chip_select reflects how this chip is wired to that master;
* it's less than num_chipselect.
*/
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*/
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*/

/* mode becomes spi_device.mode, and is essential for chips
* where the default of SPI_CS_HIGH = 0 is wrong.
*/
u8        mode;/*参考spi_device中的成员*/

/* ... may need additional spi_device chip config data here.
* avoid stuff protocol drivers can set; but include stuff
* needed to behave without being bound to a driver:
*  - quirks like clock rate mattering when not selected
*/
};

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.

struct spi_transfer {
/* it's ok if tx_buf == rx_buf (right?)
* for MicroWire, one buffer must be null
* buffers must work with dma_*map_single() calls, unless
*   spi_message.is_dma_mapped reports a pre-existing mapping
*/
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*/
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*/
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*/

dma_addr_t    tx_dma;/*如果spi_message.is_dma_mapped是真,这个是tx的dma地址*/
dma_addr_t    rx_dma;/*如果spi_message.is_dma_mapped是真,这个是rx的dma地址*/

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
传输完后,改变片选信号.这个标志可以减少系统开销*/
u8        bits_per_word;/*每个字长的比特数.如果是0,使用默认值*/
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*/
u32        speed_hz;/*通信时钟.如果是0,使用默认值*/

struct list_head transfer_list;/*用来连接的双向链表节点,用于将该transfer链入message*/
};

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.

struct spi_message {
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)*/

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
每个传输段(spi_transfer)内部的tx_buf或者是rx_buf决定的*/

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
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*/

/* REVISIT:  we might want a flag affecting the behavior of the
* last transfer ... allowing things like "read 16 bit length L"
* immediately followed by "read L bytes".  Basically imposing
* a specific message scheduling algorithm.
*
* Some controller drivers (message-at-a-time queue processing)
* could provide that as their default scheduling algorithm.  But
* others (with multi-message pipelines) could need a flag to
* tell them about such special cases.
*/

/* completion is reported through a callback */
void            (*complete)(void *context);/*用于异步传输完成时调用的回调函数*/
void            *context;/*回调函数的参数*/
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
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)*/
int            status;/*执行的结果.成功被置0,否则是一个负的错误码*/

/* for optional use by whatever driver currently owns the
* spi_message ...  between calls to spi_async and then later
* complete(), that's the spi_master controller driver.
*/
/*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*/
struct list_head    queue;/*用于将该message链入bitbang等待队列*/
void            *state;
};

spi_bitbang

struct spi_bitbang结构用于控制实际的数据传输.

struct spi_bitbang {
struct workqueue_struct    *workqueue;/*工作队列*/
struct work_struct    work;

spinlock_t        lock;
struct list_head    queue;
u8            busy;
u8            use_dma;
u8            flags;        /* extra spi->mode support */

struct spi_master    *master;/*bitbang所属的master*/

/* setup_transfer() changes clock and/or wordsize to match settings
* for this transfer; zeroes restore defaults from spi_device.
*/
int    (*setup_transfer)(struct spi_device *spi,
struct spi_transfer *t);/*用于设置设备传输时的时钟，字长等*/

void    (*chipselect)(struct spi_device *spi, int is_on);
#define    BITBANG_CS_ACTIVE    1    /* normally nCS, active low */
#define    BITBANG_CS_INACTIVE    0

/* txrx_bufs() may handle dma mapping for transfers that don't
* already have one (transfer.{tx,rx}_dma is zero), or use PIO
*/
int    (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);

/* txrx_word[SPI_MODE_*]() just looks like a shift register */
u32    (*txrx_word[4])(struct spi_device *spi,
unsigned nsecs,
u32 word, u8 bits);
};

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