[cpp]
struct spi_master { struct device dev; //内嵌的标准dev结构 /* 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; //标识的总线号 /* chipselects will be integral to many controllers; some others * might use board-specific GPIOs. */ u16 num_chipselect; /* some SPI controllers pose alignment requirements on DMAable * buffers; let protocol drivers know about these requirements. */ u16 dma_alignment; //dma对其要求 /* spi_device.mode flags understood by this controller driver */ u16 mode_bits; //代表操作的spi_device.mode /* other constraints relevant to this driver */ u16 flags; //另外的一些标志 #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); //设置模式 /* 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, //传输函数 struct spi_message *mesg); /* called on release() to free memory provided by spi_master */ void (*cleanup)(struct spi_device *spi); };而对于要操控的spi总线上的设备，其表述结构为：