前言

SPI协议是由摩托罗拉公司提出的串行通信协议，是一种高速全双工的通信总线。常见的SPI接口包含四根线，MOSI（主设备输出，从设备输入），MISO（主设备输入，从设备输出）SCLK（时钟，决定通信速率），CS（片选，用于多从机）。所以一根SPI总线也可以挂载多个设备，是用多个片选IO来区分。

时序介绍

1.空闲状态
CS脚拉高时候SPI设备处于空闲状态。
2.起始信号与终止信号
CS脚下降沿时候为起始信号 CS脚上升沿时候为停止信号。
3.数据传输（四种工作模式）
（1）CPOL=0，串行时钟空闲状态为低电平。
（2）CPOL=1，串行时钟空闲状态为高电平。
（3）CPHA=0，串行时钟的第一个跳变沿(上升沿或下降沿)采集数据。
（4）CPHA=1，串行时钟的第二个跳变沿(上升沿或下降沿)采集数据。

I2C数据结构介绍

spi_master

struct spi_master {struct device dev;//对应spi设备struct list_head list;s16          bus_num;//SPI总线号u16         num_chipselect;//片选信号的个数u16         dma_alignment;//dma buf的对齐/*控制器启动的模式位，被控制器驱动解析*/u16          mode_bits;/* bitmask of supported bits_per_word for transfers */u32         bits_per_word_mask;
#define SPI_BPW_MASK(bits) BIT((bits) - 1)
#define SPI_BIT_MASK(bits) (((bits) == 32) ? ~0U : (BIT(bits) - 1))
#define SPI_BPW_RANGE_MASK(min, max) (SPI_BIT_MASK(max) - SPI_BIT_MASK(min - 1))/* 通信速率 */u32           min_speed_hz;u32            max_speed_hz;/* other constraints relevant to this driver */u16         flags;
#define SPI_MASTER_HALF_DUPLEX  BIT(0)      /* 不能全双工*/
#define SPI_MASTER_NO_RX    BIT(1)      /* 不能读*/
#define SPI_MASTER_NO_TX    BIT(2)      /* 不能写*/
#define SPI_MASTER_MUST_RX      BIT(3)      /* 必须有读 */
#define SPI_MASTER_MUST_TX      BIT(4)      /* 必须有写*//* 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;int           (*setup)(struct spi_device *spi);//时钟和spi模式的设置函数int         (*transfer)(struct spi_device *spi,struct spi_message *mesg);//SPI的通信函数指针/* called on release() to free memory provided by spi_master */void            (*cleanup)(struct spi_device *spi);bool         (*can_dma)(struct spi_master *master,struct spi_device *spi,struct spi_transfer *xfer);/*内核线程 ，SPI控制器 用到了内核线程*/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               idling;bool             busy;bool               running;bool                rt;bool             auto_runtime_pm;bool                            cur_msg_prepared;bool               cur_msg_mapped;struct completion               xfer_completion;size_t               max_dma_len;int (*prepare_transfer_hardware)(struct spi_master *master);// 准备传输前硬件初始化int (*transfer_one_message)(struct spi_master *master,struct spi_message *mesg);int (*unprepare_transfer_hardware)(struct spi_master *master);int (*prepare_message)(struct spi_master *master,struct spi_message *message);int (*unprepare_message)(struct spi_master *master,struct spi_message *message);void (*set_cs)(struct spi_device *spi, bool enable);int (*transfer_one)(struct spi_master *master, struct spi_device *spi,struct spi_transfer *transfer);void (*handle_err)(struct spi_master *master,struct spi_message *message);/* gpio chip select */int           *cs_gpios;/* DMA channels for use with core dmaengine helpers */struct dma_chan     *dma_tx;struct dma_chan     *dma_rx;/* dummy data for full duplex devices */void            *dummy_rx;void          *dummy_tx;
};

spi_device

struct spi_device {struct device     dev;struct spi_master   *master;//设备对应控制器u32            max_speed_hz;u8         chip_select;//片选u8          bits_per_word;u16           mode;//模式（下面的#DEFINE）
#define SPI_CPHA    0x01            /* 时钟相位*/
#define SPI_CPOL    0x02            /*时钟极性 */
#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            /* CS是不是高位有效 */
#define SPI_LSB_FIRST   0x08            /* 先传输最低有效位 */
#define SPI_3WIRE   0x10            /* SI/SO signals shared */
#define SPI_LOOP    0x20            /* loopback mode */
#define SPI_NO_CS   0x40            /*只有一个从设备 无片选 */
#define SPI_READY   0x80            /* slave pulls low to pause */
#define SPI_TX_DUAL 0x100           /* 两条传输线*/
#define SPI_TX_QUAD 0x200           /* 四条传输线*/
#define SPI_RX_DUAL 0x400           /*两根线接收*/
#define SPI_RX_QUAD 0x800           /*四根线接收 */int           irq;void            *controller_state;void          *controller_data;char           modalias[SPI_NAME_SIZE];int         cs_gpio;    /* chip select gpio */
};

spi_message

struct spi_message {struct list_head transfers;struct spi_device *spi;unsigned       is_dma_mapped:1;//是否使用DMA模式/* 传输完成后的部分 */void           (*complete)(void *context);void         *context;unsigned       frame_length;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(), that's the spi_master controller driver.*/struct list_head   queue;void          *state;
};

spi_transfer

struct spi_transfer {const void  *tx_buf;//发送缓冲区void     *rx_buf;//接收缓冲区unsigned len;//缓冲区字节数/*DMA传输情况下 发送接收BUFFER的DMA地址*/dma_addr_t tx_dma;dma_addr_t   rx_dma;struct sg_table tx_sg;struct sg_table rx_sg;unsigned cs_change:1;//如果设置了，则此次传输完成后将会翻转片选unsigned   tx_nbits:3;unsigned rx_nbits:3;
#define SPI_NBITS_SINGLE    0x01 /* 1bit transfer */
#define SPI_NBITS_DUAL      0x02 /* 2bits transfer */
#define SPI_NBITS_QUAD      0x04 /* 4bits transfer */u8     bits_per_word;u16       delay_usecs;u32     speed_hz;struct list_head transfer_list;
};

SPI控制器

在drivers/spi/spi-imx.c文件中

match

static struct platform_device_id spi_imx_devtype[] = {...{.name = "imx21-cspi",.driver_data = (kernel_ulong_t) &imx21_cspi_devtype_data,}, {.name = "imx27-cspi",.driver_data = (kernel_ulong_t) &imx27_cspi_devtype_data,}, ...
};static const struct of_device_id spi_imx_dt_ids[] = {{ .compatible = "fsl,imx1-cspi", .data = &imx1_cspi_devtype_data, },{ .compatible = "fsl,imx21-cspi", .data = &imx21_cspi_devtype_data, },...
};
MODULE_DEVICE_TABLE(of, spi_imx_dt_ids);
static struct platform_driver spi_imx_driver = {.driver = {.name = DRIVER_NAME,.of_match_table = spi_imx_dt_ids,.pm = IMX_SPI_PM,},.id_table = spi_imx_devtype,.probe = spi_imx_probe,.remove = spi_imx_remove,
};
module_platform_driver(spi_imx_driver);

匹配适配器成功后运行probe函数

probe

static int spi_imx_probe(struct platform_device *pdev)
{struct device_node *np = pdev->dev.of_node;const struct of_device_id *of_id =of_match_device(spi_imx_dt_ids, &pdev->dev);struct spi_imx_master *mxc_platform_info =dev_get_platdata(&pdev->dev);struct spi_master *master;struct spi_imx_data *spi_imx;struct resource *res;int i, ret, num_cs, irq;if (!np && !mxc_platform_info) {dev_err(&pdev->dev, "can't get the platform data\n");return -EINVAL;}ret = of_property_read_u32(np, "fsl,spi-num-chipselects", &num_cs);if (ret < 0) {if (mxc_platform_info)num_cs = mxc_platform_info->num_chipselect;elsereturn ret;}/*申请一个SPI适配器*/master = spi_alloc_master(&pdev->dev,sizeof(struct spi_imx_data) + sizeof(int) * num_cs);if (!master)return -ENOMEM;platform_set_drvdata(pdev, master);master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);master->bus_num = pdev->id;//总线号master->num_chipselect = num_cs;//片选号spi_imx = spi_master_get_devdata(master);spi_imx->bitbang.master = master;/*从设备树获取片选IO*/for (i = 0; i < master->num_chipselect; i++) {int cs_gpio = of_get_named_gpio(np, "cs-gpios", i);if (!gpio_is_valid(cs_gpio) && mxc_platform_info)cs_gpio = mxc_platform_info->chipselect[i];spi_imx->chipselect[i] = cs_gpio;if (!gpio_is_valid(cs_gpio))continue;ret = devm_gpio_request(&pdev->dev, spi_imx->chipselect[i],DRIVER_NAME);if (ret) {dev_err(&pdev->dev, "can't get cs gpios\n");goto out_master_put;}}//设置相关通信的函数指针spi_imx->bitbang.chipselect = spi_imx_chipselect;spi_imx->bitbang.setup_transfer = spi_imx_setupxfer;spi_imx->bitbang.txrx_bufs = spi_imx_transfer;spi_imx->bitbang.master->setup = spi_imx_setup;spi_imx->bitbang.master->cleanup = spi_imx_cleanup;spi_imx->bitbang.master->prepare_message = spi_imx_prepare_message;spi_imx->bitbang.master->unprepare_message = spi_imx_unprepare_message;spi_imx->bitbang.master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;init_completion(&spi_imx->xfer_done);spi_imx->devtype_data = of_id ? of_id->data :(struct spi_imx_devtype_data *) pdev->id_entry->driver_data;//获取SPI的基地址并虚拟res = platform_get_resource(pdev, IORESOURCE_MEM, 0);spi_imx->base = devm_ioremap_resource(&pdev->dev, res);if (IS_ERR(spi_imx->base)) {ret = PTR_ERR(spi_imx->base);goto out_master_put;}//获取设备树中配置的中断irq = platform_get_irq(pdev, 0);if (irq < 0) {ret = irq;goto out_master_put;}//申请一个中断ret = devm_request_irq(&pdev->dev, irq, spi_imx_isr, 0,dev_name(&pdev->dev), spi_imx);if (ret) {dev_err(&pdev->dev, "can't get irq%d: %d\n", irq, ret);goto out_master_put;}//获取设备树ipgclkspi_imx->clk_ipg = devm_clk_get(&pdev->dev, "ipg");if (IS_ERR(spi_imx->clk_ipg)) {ret = PTR_ERR(spi_imx->clk_ipg);goto out_master_put;}//获取设备树perclkspi_imx->clk_per = devm_clk_get(&pdev->dev, "per");if (IS_ERR(spi_imx->clk_per)) {ret = PTR_ERR(spi_imx->clk_per);goto out_master_put;}ret = clk_prepare_enable(spi_imx->clk_per);if (ret)goto out_master_put;ret = clk_prepare_enable(spi_imx->clk_ipg);if (ret)goto out_put_per;//设置spi clkspi_imx->spi_clk = clk_get_rate(spi_imx->clk_per);/** Only validated on i.mx6 now, can remove the constrain if validated on* other chips.*/if ((spi_imx->devtype_data == &imx51_ecspi_devtype_data|| spi_imx->devtype_data == &imx6ul_ecspi_devtype_data)&& spi_imx_sdma_init(&pdev->dev, spi_imx, master, res))dev_err(&pdev->dev, "dma setup error,use pio instead\n");spi_imx->devtype_data->reset(spi_imx);spi_imx->devtype_data->intctrl(spi_imx, 0);master->dev.of_node = pdev->dev.of_node;ret = spi_bitbang_start(&spi_imx->bitbang);//此函数用于将spi_bitbang的参数进行初始化if (ret) {dev_err(&pdev->dev, "bitbang start failed with %d\n", ret);goto out_clk_put;}dev_info(&pdev->dev, "probed\n");clk_disable_unprepare(spi_imx->clk_ipg);clk_disable_unprepare(spi_imx->clk_per);return ret;out_clk_put:clk_disable_unprepare(spi_imx->clk_ipg);
out_put_per:clk_disable_unprepare(spi_imx->clk_per);
out_master_put:spi_master_put(master);return ret;
}

spi_bitbang_start

int spi_bitbang_start(struct spi_bitbang *bitbang)
{struct spi_master *master = bitbang->master;int ret;if (!master || !bitbang->chipselect)return -EINVAL;spin_lock_init(&bitbang->lock);if (!master->mode_bits)master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;if (master->transfer || master->transfer_one_message)return -EINVAL;/*设置适配器传输消息的函数指针*/master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;master->transfer_one_message = spi_bitbang_transfer_one;if (!bitbang->txrx_bufs) {bitbang->use_dma = 0;bitbang->txrx_bufs = spi_bitbang_bufs;if (!master->setup) {if (!bitbang->setup_transfer)bitbang->setup_transfer =spi_bitbang_setup_transfer;master->setup = spi_bitbang_setup;master->cleanup = spi_bitbang_cleanup;}}/* driver may get busy before register() returns, especially* if someone registered boardinfo for devices*/ret = spi_register_master(spi_master_get(master));if (ret)spi_master_put(master);return 0;
}

static int spi_bitbang_transfer_one(struct spi_master *master,struct spi_message *m)
{struct spi_bitbang *bitbang;unsigned       nsecs;struct spi_transfer   *t = NULL;unsigned     cs_change;int           status;int          do_setup = -1;struct spi_device    *spi = m->spi;bitbang = spi_master_get_devdata(master);/* FIXME this is made-up ... the correct value is known to* word-at-a-time bitbang code, and presumably chipselect()* should enforce these requirements too?*/nsecs = 100;cs_change = 1;status = 0;list_for_each_entry(t, &m->transfers, transfer_list) {/* override speed or wordsize? */if (t->speed_hz || t->bits_per_word)do_setup = 1;/* init (-1) or override (1) transfer params */if (do_setup != 0) {if (bitbang->setup_transfer) {status = bitbang->setup_transfer(spi, t);//设置时钟极性if (status < 0)break;}if (do_setup == -1)do_setup = 0;}/* set up default clock polarity, and activate chip;* this implicitly updates clock and spi modes as* previously recorded for this device via setup().* (and also deselects any other chip that might be* selected ...)*/if (cs_change) {bitbang->chipselect(spi, BITBANG_CS_ACTIVE);//片选激活ndelay(nsecs);}cs_change = t->cs_change;if (!t->tx_buf && !t->rx_buf && t->len) {status = -EINVAL;break;}/* transfer data.  the lower level code handles any* new dma mappings it needs. our caller always gave* us dma-safe buffers.*/if (t->len) {/* REVISIT dma API still needs a designated* DMA_ADDR_INVALID; ~0 might be better.*/if (!m->is_dma_mapped)t->rx_dma = t->tx_dma = 0;status = bitbang->txrx_bufs(spi, t);//传输数据 也就是probe设置对应的spi_imx_transfer函数}if (status > 0)m->actual_length += status;if (status != t->len) {/* always report some kind of error */if (status >= 0)status = -EREMOTEIO;break;}status = 0;/* protocol tweaks before next transfer */if (t->delay_usecs)udelay(t->delay_usecs);if (cs_change &&!list_is_last(&t->transfer_list, &m->transfers)) {/* sometimes a short mid-message deselect of the chip* may be needed to terminate a mode or command*/ndelay(nsecs);bitbang->chipselect(spi, BITBANG_CS_INACTIVE);ndelay(nsecs);}}...
}

发送流程


spi_message_init();     /* 初始化spi_message */
spi_message_add_tail();/* 将spi_transfer添加到spi_message队列 */
spi_sync(); /* 同步发送 */->__spi_sync()->__spi_pump_messages()-> master->transfer_one_message()-> master->transfer_one_message = spi_bitbang_transfer_one;-> spi_imx->bitbang.txrx_bufs = spi_imx_transfer;-> bitbang->txrx_bufs(spi, t);->spi_imx_transfer()->spi_imx_pio_transfer()->spi_imx_push()->spi_imx->tx(spi_imx);//spi_imx_setupxfer中设置好了发送函数以U8来说->spi_imx_buf_tx_u8()static void spi_imx_buf_tx_u8(struct spi_imx_data *spi_imx)
{                                   type val = 0;                                                          if (spi_imx->tx_buf) {                       val = *(type *)spi_imx->tx_buf;             spi_imx->tx_buf += sizeof(type);           }                                                           spi_imx->count -= sizeof(type);                                         writel(val, spi_imx->base + MXC_CSPITXDATA);
}

函数介绍

/*注册和释放spi驱动*/
int spi_register_driver(struct spi_driver *sdrv);
void spi_unregister_driver(struct spi_driver *sdrv);static void spi_message_init(struct spi_message *m);//消息初始化
void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)//将spi_transfer添加到spi_message队列
int spi_sync(struct spi_device *spi, struct spi_message *message)//同步发送
int spi_async(struct spi_device *spi, struct spi_message *message)//异步发送

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前言