SPI子系统

这些驱动的共同点：

• 主机端驱动和外设端驱动分离

• 通过一个核心层将某种总线协议进行抽象

• 外设端驱动通过核心层API间接调用主机驱动提供的传输函数进行收发数据

• IIC、SPI等不支持热拔插的总线需要板级信息描述，对于USB、PCI等支持热拔插的总线则不需要板级描述信息

通过以上可以看到Linux下的SPI子系统和IIC、USB等子系统框架特别类似，都是分为两部分：主机控制器驱动和设备驱动

SPI 子系统体系结构

主机控制器驱动

include\linux\spi\spi.hlinux使用struct spi_controller描述主机控制器

#define spi_master          spi_controllerstructspi_controller {structdevicedev;structlist_headlist;    s16            bus_num;    u16            num_chipselect;  /* 片选信号数量 */    ....../* 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))/* limits on transfer speed */    u32            min_speed_hz;    u32            max_speed_hz;/* other constraints relevant to this driver */    u16            flags;#define SPI_CONTROLLER_HALF_DUPLEX    BIT(0)    /* can't do full duplex */#define SPI_CONTROLLER_NO_RX        BIT(1)    /* can't do buffer read */#define SPI_CONTROLLER_NO_TX        BIT(2)    /* can't do buffer write */#define SPI_CONTROLLER_MUST_RX        BIT(3)    /* requires rx */#define SPI_CONTROLLER_MUST_TX        BIT(4)    /* requires tx */#define SPI_MASTER_GPIO_SS        BIT(5)    /* GPIO CS must select slave *//* flag indicating this is an SPI slave controller */bool            slave;/*     * on some hardware transfer / message size may be constrained     * the limit may depend on device transfer settings     */size_t (*max_transfer_size)(struct spi_device *spi);size_t (*max_message_size)(struct spi_device *spi);/* I/O mutex */structmutexio_mutex;/* lock and mutex for SPI bus locking */spinlock_t        bus_lock_spinlock;structmutexbus_lock_mutex;/* flag indicating that the SPI bus is locked for exclusive use */bool            bus_lock_flag;int            (*setup)(struct spi_device *spi);int            (*transfer)(struct spi_device *spi,struct spi_message *mesg);/* called on release() to free memory provided by spi_controller */void            (*cleanup)(struct spi_device *spi);bool            (*can_dma)(struct spi_controller *ctlr,struct spi_device *spi,struct spi_transfer *xfer);    ......structspi_message        *cur_msg;bool                idling;bool                busy;bool                running;bool                rt;bool                auto_runtime_pm;bool                            cur_msg_prepared;bool                cur_msg_mapped;structcompletionxfer_completion;size_t                max_dma_len;    ....../* gpio chip select */int            *cs_gpios;int (*fw_translate_cs)(struct spi_controller *ctlr, unsigned cs);};

• 重点关注transfer成员函数，类似I2C，SPI也是最终调用该函数实现数据传输，SPI的数据以struct spi_message形式组织起来，添加到子系统维护的队列中进行发送。

SPI主机控制器驱动相关API

1、spi_master申请/释放

/* the spi driver core manages memory for the spi_controller classdev */externstructspi_controller *__spi_alloc_controller(structdevice *host,unsignedintsize, boolslave);staticinlinestruct spi_controller *spi_alloc_master(struct device *host,unsignedint size){return __spi_alloc_controller(host, size, false);}#define spi_master_put(_ctlr)       spi_controller_put(_ctlr)staticinlinevoidspi_controller_put(struct spi_controller *ctlr){if (ctlr)        put_device(&ctlr->dev);}

2、spi_master注册/注销

#define spi_register_master(_ctlr)  spi_register_controller(_ctlr)intspi_register_controller(struct spi_controller *ctlr)#define spi_unregister_master(_ctlr)    spi_unregister_controller(_ctlr)voidspi_unregister_controller(struct spi_controller *ctlr)

SPI控制器驱动在设备树中的节点

  ecspi3: ecspi@2010000 {#address-cells = <1>;#size-cells = <0>;      compatible = "fsl,imx6ul-ecspi", "fsl,imx51-ecspi";  //匹配属性      reg = <0x20100000x4000>;      interrupts = 33 IRQ_TYPE_LEVEL_HIGH>;      clocks = <&clks IMX6UL_CLK_ECSPI3>,      <&clks IMX6UL_CLK_ECSPI3>;      clock-names = "ipg", "per";      dmas = <&sdma 771>, <&sdma 872>;      dma-names = "rx", "tx";      status = "disabled";};

分别搜索compatible = "fsl,imx6ul-ecspi", "fsl,imx51-ecspi"的两个字符串内容就可以找到SOC相对应的SPI主机驱动在哪个文件中实现

设备驱动

SPI设备驱动分成两部分：

• spi_driver类 ，spi驱动描述如何操作设备
• spi_device 类   ，spi设备信息，也就是硬件信息

与platform_driver和platform_device类似

spi_driver注册/注销

intspi_register_driver(struct spi_driver *sdrv)  注册一个spi驱动voidspi_unregister_driver(struct spi_driver *sdrv)  注销一个spi驱动

设备驱动的设备树节点示例

&ecspi1 {    fsl,spi-num-chipselects = <1>;           /* 片选引脚数 */    cs-gpios = <&gpio4 260>;                /* 片选引脚 */    pinctrl-names = "default";    pinctrl-0 = <&pinctrl_ecspi1>;    status = "okay";    xgj_oled@0 {        dc-gpios = <&gpio4 240>;            /* 命令数据选择引脚 */        rst-gpios = <&gpio1 20>;            /* 复位引脚 */        compatible = "xgj,oled";             /* 匹配属性 */        spi-max-frequency = <20000000>;      /* 时钟频率 */        reg = <0>;                           /* 0 通道 */    };    };

• 设备挂在哪个spi下就追加子节点到哪个spi控制器的设备树节点下，此处&ecspi1 追加到spi1下
• xgj_oled，追加的设备节点名

SPI数据收发

内核使用spi_tranfer类描述数据传输

structspi_transfer {constvoid  *tx_buf;         //发送的bufvoid        *rx_buf;         //接收数据的bufunsigned    len;dma_addr_t  tx_dma;dma_addr_t  rx_dma;structsg_tabletx_sg;structsg_tablerx_sg;unsigned    cs_change:1;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;structlist_headtransfer_list;};

SPI传输数据还要组织成struct spi_message的形式添加到队列中进行传输

Linux中的SPI消息被抽象成spi_message类

structspi_message {structlist_headtransfers;structspi_device   *spi;unsigned        is_dma_mapped:1;/* completion is reported through a callback */void            (*complete)(void *context);   //发送接收完成该函数会被调用void            *context;unsigned        frame_length;unsigned        actual_length;int         status;structlist_headqueue;void            *state;/* list of spi_res reources when the spi message is processed */structlist_headresources;};

//初始化spi_message和添加spi_transferstaticinlinevoidspi_message_init(struct spi_message *m);  //初始化spi_messagestaticinlinevoidspi_message_add_tail(struct spi_transfer *t, struct spi_message *m); //将spi_tranfer加入spi_message的消息队列中，在加入spi_tranfer之前必须先初始化spi_messageintspi_async(struct spi_device *spi, struct spi_message *message); //SPI异步传输数据intspi_sync(struct spi_device *spi, struct spi_message *message); //SPI同步传输数据

示例：

/* SPI 多字节发送 */staticintspi_send(struct spi_device *spi, u8 *buf, int len){ int ret; structspi_messagem;structspi_transfert = {         .tx_buf = buf,         .len = len,     };     spi_message_init(&m);         /* 初始化 spi_message */    spi_message_add_tail(t, &m);/* 将 spi_transfer 添加到 spi_message 队列 */    ret = spi_sync(spi, &m);     /* 同步传输 */return ret; }/* SPI 多字节接收 */staticintspi_receive(struct spi_device *spi, u8 *buf, int len){ int ret; structspi_messagem;structspi_transfert = {         .rx_buf = buf,         .len = len,     };     spi_message_init(&m);         /* 初始化 spi_message */    spi_message_add_tail(t, &m);/* 将 spi_transfer 添加到 spi_message 队列 */    ret = spi_sync(spi, &m);     /* 同步传输 */return ret; }

SPI驱动编写模板

#include<linux/init.h>#include<linux/module.h>#include<linux/fs.h>#include<linux/cdev.h>#include<linux/uaccess.h>#include<linux/types.h>#include<linux/kernel.h>#include<linux/delay.h>#include<linux/ide.h>#include<linux/errno.h>#include<linux/gpio.h>#include<asm/mach/map.h>#include<linux/of.h>#include<linux/of_address.h>#include<linux/of_gpio.h>#include<asm/io.h>#include<linux/device.h>#include<linux/timer.h>#include<linux/jiffies.h>#include<linux/platform_device.h>#include<linux/of_irq.h>#include<linux/wait.h>#include<linux/sched/signal.h>#include<linux/poll.h>#include<linux/atomic.h>#include<linux/spi/spi.h>structxxx_device {int dc_gpio;int rst_gpio;dev_t dev_no; /* 设备号 */structcdevchrdev;structclass *class;structspi_device *spi;};staticstructxxx_device *xxx_dev;staticint _drv_open(struct inode *node, struct file *file){int ret = 0;    ......return0;}staticssize_t _drv_read(struct file *filp, char __user *buf, size_t size, loff_t *offset){int ret = 0;    ...return ret;}staticlong _drv_ioctl(struct file *filp, unsignedint cmd, unsignedlong arg){int ret = 0;switch (cmd)    {case CMD1 :break;case CMD2 :break;        ......        ......    }return ret;}staticint _drv_release(struct inode *node, struct file *filp){return0;}staticstructfile_operationsxxx_drv_ops = {    .owner = THIS_MODULE,    .open = _drv_open,    .read = _drv_read,    .unlocked_ioctl = _drv_ioctl,    .release = _drv_release,};staticint _driver_probe(struct spi_device *spi){int err = 0;structdevice *_dev;structdevice_node *_dts_node;    ......    ....../* 内核自动分配设备号 */    err = alloc_chrdev_region(&xxx_dev->dev_no, 0, 1, DEV_NAME);if (err < 0)    {        pr_err("Error: failed to register xxx, err: %d\n", err);goto exit_free_dev;    }    cdev_init(&xxx_dev->chrdev, &xxx_drv_ops);    err = cdev_add(&xxx_dev->chrdev, xxx_dev->dev_no, 1);if (err)    {        printk("cdev add failed\r\n");goto exit_unregister;    }    xxx_dev->class = class_create(THIS_MODULE, DEV_NAME);if (IS_ERR(xxx_dev->class))    {        err = PTR_ERR(xxx_dev->class);goto exit_cdev_del;    }/* 使驱动自动在用户空间创建设备节点 */    _dev = device_create(xxx_dev->class, NULL, xxx_dev->dev_no, NULL, DEV_NAME);if (IS_ERR(_dev))    { /* 判断指针是否合法 */        err = PTR_ERR(_dev);goto exit_class_del;    }    xxx_dev->spi = spi;gotoexit;exit_class_del:    class_destroy(xxx_dev->class);exit_cdev_del:    cdev_del(&xxx_dev->chrdev);exit_unregister:    unregister_chrdev_region(xxx_dev->dev_no, 1); /* 注销设备 */exit_free_dev:    kfree(xxx_dev);    xxx_dev = NULL;exit:return err;}staticint _driver_remove(struct spi_device *spi){int ret = 0;    device_destroy(xxx_dev->class, xxx_dev->dev_no);    class_destroy(xxx_dev->class);    cdev_del(&xxx_dev->chrdev);    unregister_chrdev_region(xxx_dev->dev_no, 1); /* 注销设备 */    kfree(xxx_dev);return ret;}/* 设备树的匹配列表 */staticstructof_device_idxxx_of_match_table[] = {    {.compatible = "xxx"}, /* 通过设备树来匹配 */    {},};/* 传统匹配方式 ID 列表 */staticconststructspi_device_idxxx_id_table[] = {    {.name = "xxx", 0},    {}};/* SPI 驱动结构体 */staticstructspi_driverxxx_driver = {    .probe = _driver_probe,    .remove = _driver_remove,    .driver = {        .owner = THIS_MODULE,        .name = "xxx,dev",        .of_match_table = xxx_of_match_table,    },    .id_table = xxx_id_table,};module_spi_driver(xxx_driver);MODULE_AUTHOR("Ares");MODULE_LICENSE("GPL");