spi-driver设备驱动

1、SPI主机驱动（类似I2C适配驱动）
    Linux内核使用spi_master表示SPI主机驱动，spi_master是一个结构体，定义在include/linux/spi/spi.h中
    struct spi_master {
        struct device dev;
        struct list_head list;
        ......
        s16 bus_num;
        s16 num_chipselect;
        u16 dma_alignment;
        u16 mode_bits;
        u32 bits_per_word_mask;
        ......
        u32 min_speed_hz;
        u32 max_speed_hz;
        u16 flags;
        ......
        spinlock_t bus_lock_spinlock;
        struct mutex bus_lock_mutex;
        bool bus_lock_flag;
        ......
        int (*setup)(struct spi_device *spi);
        ......
        int (*transfer)(*struct spi_device *spi, struct spi_message *mesg);
        int (*transfer_one_message)(struct spi_master *master, struct spi_message *mesg);
        ......
    };
    ①、spi_master申请与释放
        struct spi_master *spi_alloc_master(struct device *dev, unsigned size); 、、申请
        void spi_master_put(struct spi_master *master); //释放
    ②、spi_master的注册与注销
        int spi_register_master(struct spi_master *master); //注册
        void spi_unregister_master(struct spi_master *master); //注销
        spi_bitbang_start()/spi_bitbang_stop()也是一对注册/注销


2、SPI设备驱动
    Linux内核使用spi_driver结构体来表示spi设备驱动,spi_driver定义在include/linux/spi/spi.h 文件中
    struct spi_driver {
        const struct spi_device_id *id_table;
        int (*probe)(struct spi_device *spi);
        int (*remove)(struct spi_device *spi);
        void (*shutdown)(struct spi_device *spi);
        struct device_driver driver;
    };
    ①、驱动注册、注销
        int spi_register_driver(struct spi_driver *sdrv);
        void spi_unregister_driver(struct spi_master *sdrv);
    ②、注册流程
        static int xxx_probe(struct spi_driver *spi)
        {
            ......
            return 0;
        }
        static int xxx_remove(struct spi_device *spi)
        {
            ......
            return 0;
        }
        //传统匹配方式ID表
        static const struct spi_device_id xxx_id[] = {
            {"xxx", 0},
            {},
        };
        //设备树匹配表
        static const struct of_device_id xxx_of_match[] = {
            {.compatible = "xxx"},
            {/* sentinel */}
        };
        static struct spi_driver xxx_driver = {
            .probe = xxx_probe,
            .remove = xxx_remove,
            .driver = {
                .owner = THIS_MODULE,
                .name = "xxx",
                .of_match_table = xxx_of_match,
            },
            .id_table = xxx_id,
        };
        static int __init xxx_init(void)
        {
            return spi_register_driver(&xxx_driver);
        }
        static void __exit xxx_exit(void)
        {
            spi_unregister_driver(&xxx_driver);
        }
        module_init(xxx_init);
        module_exit(xxx_exit);

3、spi设备与驱动匹配
    由SPI总线完成匹配，SPI总线为spi_bus_type 结构体定义在driver/spi/spi.c文件中
    struct bus_type spi_bus_type ={
        .name = "spi",
        .dev_groups = spi_dev_groups,
        .match = spi_match_device,
        .uevent = spi_uevent,
    };

4、设备区别编写流程
    ①、IO的pinctrl子节点创建或修改（重点检查对应的IO是否有给其他设备使用了，注意删除）
        pinctrl_ecspi3: icm20608{
            fsl,pins = <
                MX6UL_PAD_UART2_TX_DATA__GPIO1_IO20 0x10b0 /* CS */
                MX6UL_PAD_UART2_RX_DATA__ECSPI3_SCLK 0x10b1 /* SCLK */
                MX6UL_PAD_UART2_RTS_B__ECSPI3_MISO 0x10b1 /* MISO */
                MX6UL_PAD_UART2_CTS_B__ECSPI3_MOSI 0x10b1 /* MOSI */
            >;
        };

        &ecspi3 {
            fsl,spi-num-chipselects = <1>; //ecspi1总线上只挂载了一从设备
            cs-gpios = <&gpio1 20 GPIO_ACTIVE_LOW>; //CS片选信号GPIO1_IO20
            pinctrl-names = "default";
            pinctrl-0 = <&pinctrl_ecspi3>;
            status = "okay";

            spidev:icm20608@0 {
                compatible = "alpha, icm20608"; //匹配st的设备驱动
                spi-max-frequency = <10000000>;
                reg = <0>; //使用ecspi3的通道0，与icm20608@0一致，这个是CS片选？
            };
        };

    ②、spi设备数据收发处理流程
        (1)申请并初始化spi_transfer,设置tx_buf,rx_buf,len等参数
        (2)使用spi_message_init函数初始化spi_message
        (3)使用spi_message_add_tail函数把之前设置好的spi_transfer添加到spi_message队列中
        (4)使用spi_syn函数完成SPI数据同步传输
        //spi 多字节发送
        static int spi_send(struct spi_device *spi, u8 *buf, int len)
        {
            int ret;
            struct spi_message m;
            struct spi_transfer t={
                .tx_buf = buf,
                .len = len,
            };

            spi_message_init(&m);
            spi_message_add_tail(t, &m);
            ret = spi_sync(spi, &m);
            return ret;
        }
        //spi 多字节接收
        static int spi_receive(struct spi_device *spi, u8 *buf, int len)
        {
            int ret;
            struct spi_message m;
            struct spi_transfer t={
                .rx_buf = buf,
                .len = len,
            };

            spi_message_init(&m);
            spi_message_add_tail(t, &m);
            ret = spi_sync(spi, &m);
            return ret;

        }