SPI在linux3.14.78 FS_S5PC100（Cortex A8）和S3C2440上驱动移植(deep dive)

　　由于工作的原因，对SPI的理解最为深刻，也和SPI最有感情了，之前工作都是基于OSEK操作系统上进行实现，也在US/OS3上实现过SPI驱动的实现和测试，但是都是基于基本的寄存器操作，没有一个系统软件架构的思想，感觉linux SPI驱动很强大，水很深，废话少说，SPI总线上有两类设备：一类是主机端，通常作为SOC系统的一个子模块出现，比如很多嵌入式MPU中都常常包含SPI模块。一类是从机被控端，例如一些SPI接口的Flash、传感器等等。主机端是SPI总线的控制者，通过使用SPI协议主动发起SPI总线上的会话。而受控端则被动接受SPI主控端的指令，并作出响应的响应，本文读者前提是必须熟练掌握linux Platform总线驱动模型 和基本字符设备驱动的实现。

　　SPI总线由MISO（串行数据输入）、MOSI（串行数据输出）、SCK（串行移位时钟）、CS（使能信号）4个信号线组成。SPI常用四种数据传输模式，主要差别在于：输出串行同步时钟极性（CPOL）和相位（CPHA）可以进行配置。如果CPOL= 0，串行同步时钟的空闲状态为低电平；如果CPOL= 1，串行同步时钟的空闲状态为高电平。如果CPHA= 0，在串行同步时钟的前沿（上升或下降）数据被采样；如果CPHA = 1，在串行同步时钟的后沿（上升或下降）数据被采样。同I2C子系统类似，SPI子系统分为3个部分，分别是SPI核心层、主控制器驱动和协议驱动，通俗一点就是SPI核心层主要完成1.定义并注册SPI总线spi_bus_type和控制器类spi_master_class;2.提供spi_driver,spi_device和spi_master的分配，创建，注册和注销；3.实现SPI通信方法的上层代码。主控制器驱动对应I2C的适配器驱动，SPI用spi_master来描述相应的控制器，通常用spi_bitbang来控制实际的数据传输，功能非常类似与i2c_algorithm。协议驱动类比I2C设备驱动，可以理解成客户端驱动，下面详细分析和实现基于linux3.14.78内核版本 SPI在S3C2440/6410上驱动移植.

　　Step1，实现SPI控制器的设备接口（相对应有两种方式，一种实现方式是S3c2440纯粹通过配置来实现，另一种实现方式针对m25p10，独立编写单独的spi驱动模块）

　　首先针对S3C2440，SPI控制器的设备接口在drivers/spi/spidev.c中实现，下图为相应的软件流程图，spidev.c中的spidev_init()作为模块初始化函数，在系统启动或者模块加载是被调用，主要完成以下三种操作：

　　1、调用register_chrdev()为SPI控制器注册主设备号为153，次设备号范围为0~255，文件操作集合为spidev_fops的字符设备；

　　2、调用class_create（）注册一个名为“spidev”的设备类；

　　3、调用spi_register_driver（）向系统添加SPI控制器的设备驱动spidev_spi；

　　spi_register_driver（）将驱动spidev_spi添加到SPI核心层注册的spi_bus_type总线上，注意，该总线属于spi总线，Spi总线对应的总线类型为spi_bus_type，在内核的drivers/spi/spi.c中定义，对应的匹配规则是（高版本中的匹配规则会稍有变化，引入了id_table，可以匹配多个spi设备名称）详见以下代码。由于spi总线的匹配方式是检查spi_device.modalias与spi_driver.driver.name是否相同，而spidev_spi的driver.name是“spidev”,so 只有spi_bus_type总线上的modalias为“spidev”的设备，才可以与spidev_spi驱动匹配。由于S3C2440拥有两个SPI控制器，对应的平台信息是s3c_device_spi0和s3c_device_spi1,可以将其添加到机器配置文件的My2440_devices数组中，驱动中probe方法中用到的总线编号、片选总数等信息来源于平台数据，这些数据需要用户添加，添加方式有两种，平台设备的平台数据类型是S3C2410_SPI_info，在板级初始化文件中可以为两个SPI平台设备分别定义和添加这些平台数据，此外为了支持SPI控制器设备接口功能，还需要在机器配置文件为SPI控制器设备添加并注册spi_board_info对象，详见下面代码。

　　设备与驱动匹配后，通过调用spidev_spi的probe方法来绑定工作见代码。SPI控制器设备操作集合是spidev_fops，主要包括spidev_write,spidev_read,spidev_ioctl,spidev_open和spidev_release。下面的代码注释中详尽分析了spidev_read（）函数的实现过程，spidev_write（）的分析和实现方法与read类似，spidev_open（）会遍历device_list链表，找出其中设备号与打开设备文件的inode.i_rdev相等的spidev_data对象，并将该对象记录在文件的私有数据filp->private_data中，以供read和write函数获取，此外要实现全双工的传输需要借助控制器设备的ioctl方法，对应实现函数是spidev_ioctl()，全双工传输也是通过spidev_sync()完成的，与半双工传输唯一不同的是在消息的传输段中，tx_buffer和rx_buffer同时被设置，它还提供获取和修改时钟模式、子宽、最大时钟频率属性的命令。

 static struct s3c2410_spi_info s3c2410_spi0_platdata = {
     .pin_cs = S3C2410_GPG2,
     .num_cs = ,
     .bus_num = ,
     .gpio_setup = s3c24xx_spi_gpiocfg_bus0_gpe11_12_13,
 };
 static struct spi_board_info s3c2410_spi0_board[] =
 {
     [] = {
         .modalias = "spidev",
         .bus_num = ,
         .chip_select = ,
         .max_speed_hz =  * ,
     },
     [] = {
         .modalias = "at25",
         .platform_data = &at25_eeprom_data,
         .bus_num = ,
         .chip_select = ,
         .max_speed_hz =  * ,
     }
 };
 static struct s3c2410_spi_info s3c2410_spi1_platdata = {
     .pin_cs = S3C2410_GPG3,
     .num_cs = ,
     .bus_num = ,
     .gpio_setup = s3c24xx_spi_gpiocfg_bus1_gpg5_6_7,
 };
 static struct spi_board_info s3c2410_spi1_board[] =
 {
     [] = {
         .modalias = "spidev",
         .bus_num = ,
         .chip_select = ,
         .max_speed_hz =  * ,
     }
 };
 static void __init My2440_machine_init(void)
 {
 s3c24xx_fb_set_platdata(&My2440_fb_info);
 s3c_i2c0_set_platdata(NULL);
 i2c_register_board_info(, i2c_devices, ARRAY_SIZE(i2c_devices));
 s3c_device_spi0.dev.platform_data= &s3c2410_spi0_platdata;
 spi_register_board_info(s3c2410_spi0_board, ARRAY_SIZE(s3c2410_spi0_board));
 s3c_device_spi1.dev.platform_data= &s3c2410_spi1_platdata;
 spi_register_board_info(s3c2410_spi1_board, ARRAY_SIZE(s3c2410_spi1_board));
 s3c_device_nand.dev.platform_data = &My2440_nand_info;
 s3c_device_sdi.dev.platform_data = &My2440_mmc_cfg;
 platform_add_devices(My2440_devices, ARRAY_SIZE(My2440_devices));
 }   

 struct bus_type spi_bus_type = {
                 .name = "spi",
                 .dev_attrs = spi_dev_attrs,
                 .match = spi_match_device,
                 .uevent = spi_uevent,
                 .suspend = spi_suspend,
                 .resume = spi_resume,
         };

 static int spi_match_device(struct device *dev, struct device_driver *drv)
         {
                 const struct spi_device *spi = to_spi_device(dev);
                 return strcmp(spi->modalias, drv->name) == ;
         }

static int spidev_probe(struct spi_device *spi)
{
    struct spidev_data    *spidev;
    int            status;
    unsigned long        minor;
    /* Allocate driver data, 分配并初始化一个spidev_data对象，用来描述SPI控制器设备驱动操作的控制器设备，包含它的设备号，传输缓存和内嵌spi_device*/
    spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
    if (!spidev)
        return -ENOMEM;
    /* Initialize the driver data ，将与spidev_spi驱动匹配的spi_device赋值给spidev_data.spi，通过find_first_zero_bit()从位图minors中分配到次设备号，
　　与主设备号SPIDEV_MAJOR构成设备号并赋值给spidev_data.devt,然后调用device_create（）在/dev下创建名称格式为“spidev%d%d”的字符设备文件，第一个%d表示控制器编号，
　　即spi_device.master.bus_num，第二个对应片选号，即spi_device.chip_select*/
    spidev->spi = spi;
    spin_lock_init(&spidev->spi_lock);
    mutex_init(&spidev->buf_lock);
    INIT_LIST_HEAD(&spidev->device_entry);
    /* If we can allocate a minor number, hook up this device.
     * Reusing minors is fine so long as udev or mdev is working.
     */
    mutex_lock(&device_list_lock);
    minor = find_first_zero_bit(minors, N_SPI_MINORS);
    if (minor < N_SPI_MINORS) {
        struct device *dev;
        spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
        dev = device_create(spidev_class, &spi->dev, spidev->devt,
                    spidev, "spidev%d.%d",
                    spi->master->bus_num, spi->chip_select);
        status = PTR_ERR_OR_ZERO(dev);
    } else {
        dev_dbg(&spi->dev, "no minor number available!\n");
        status = -ENODEV;
    }
    if (status == ) {
        set_bit(minor, minors);
/*将spidev_data对象添加到一个名为device_list的设备列表中，最后将spidev_data对象设置为对应spi_device的驱动数据，将其值赋值给dpi_device.dev.driver_data*/
        list_add(&spidev->device_entry, &device_list);
    }
    mutex_unlock(&device_list_lock);
    if (status == )
        spi_set_drvdata(spi, spidev);
    else
        kfree(spidev);
    return status;
}

/*spidev_read(),spidev_write()实现的读写操作都是半双工的传输，要实现全双工传输需要调用spidev_ioctl（）操作，在spidev_read（）中，通过调用spidev_sync_read()
　　同步读取指定长度数据到spidev_data_buffer中，然后调用copy_to_user()将读取的数据复制到用户空间缓冲*/

static ssize_t spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
    struct spidev_data    *spidev;
    ssize_t            status = ;
    /* chipselect only toggles at start or end of operation */
    if (count > bufsiz)
        return -EMSGSIZE;
    spidev = filp->private_data;
    mutex_lock(&spidev->buf_lock);
    status = spidev_sync_read(spidev, count);
    if (status > ) {
        unsigned long    missing;
        missing = copy_to_user(buf, spidev->buffer, status);
        if (missing == status)
            status = -EFAULT;
        else
            status = status - missing;
    }
    mutex_unlock(&spidev->buf_lock);
    return status;
}

/*spidev_sync_read（）中定义一个spi_transfer和spi_message对象，使用spidev_data.buffer初始化spi_transfer.rx_buf，
　　然后将spi_transfer对象添加到spi_message中，调用spidev_sync()传输信息；*/

spidev_sync_read(struct spidev_data *spidev, size_t len)

{
    struct spi_transfer    t = {
            .rx_buf        = spidev->buffer,
            .len        = len,
        };
    struct spi_message    m;
    spi_message_init(&m);
    spi_message_add_tail(&t, &m);
    return spidev_sync(spidev, &m);
}

/*spidev_sync()实现同步传输的机制：首先为传入的消息对象的complete和context成员赋值，context被设置为完成接口done，complete被设置成spidev_complete（），然后
调用spi_async()启动异步传输，spi_async()返回后，通过调用wait_for_completion（）阻塞调用进程，直到异步传输完成，spi_message的complete方法，即spidev_complete（）
被调用来唤醒被阻塞的进程，异步传输接口函数spi_async()属于SPI核心层，在include/linux/spi/spi.h中定义并实现，它只调用了spi_device所属控制器的transfer方法*/
static ssize_t spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
    DECLARE_COMPLETION_ONSTACK(done);
    int status;
    message->complete = spidev_complete;
    message->context = &done;
    spin_lock_irq(&spidev->spi_lock);
    if (spidev->spi == NULL)
        status = -ESHUTDOWN;
    else
        status = spi_async(spidev->spi, message);
    spin_unlock_irq(&spidev->spi_lock);

    if (status == ) {
        wait_for_completion(&done);
        status = message->status;
        if (status == )
            status = message->actual_length;
    }
    return status;
}

针对FS_S5PC100上的M25P10芯片，

//spi_device对应的含义是挂接在spi总线上的一个设备，所以描述它的时候应该明确它自身的设备特性、传输要求、及挂接在哪个总线上
static struct spi_board_info s3c_spi_devs[] __initdata = {
                {
                        .modalias = "m25p10",
                        .mode = SPI_MODE_0,    //CPOL=0, CPHA=0 此处选择具体数据传输模式
                        .max_speed_hz = ,    //最大的spi时钟频率
                        /* Connected to SPI-0 as 1st Slave */
                        .bus_num = ,    //设备连接在spi控制器0上
                        .chip_select = ,    //片选线号，在S5PC100的控制器驱动中没有使用它作为片选的依据，而是选择了下文controller_data里的方法
                        .controller_data = &smdk_spi0_csi[],
                },
        };
        static struct s3c64xx_spi_csinfo smdk_spi0_csi[] = {
                [] = {
                        .set_level = smdk_m25p10_cs_set_level,
                        .fb_delay = 0x3,
                },
        };
        static void smdk_m25p10_cs_set_level(int high)    //spi控制器会用这个方法设置cs
        {
                u32 val;
                val = readl(S5PC1XX_GPBDAT);
                if (high)
                        val |= (<<);
                else
                        val &= ~(<<);
                writel(val, S5PC1XX_GPBDAT);
        }
spi_register_board_info(s3c_spi_devs, ARRAY_SIZE(s3c_spi_devs));//注册spi_board_info,这个代码会把spi_board_info注册要链表board_list上。
//spi_master的注册会在spi_register_board_info之后，spi_master注册的过程中会调用scan_boardinfo扫描board_list，找到挂接在它上面的spi设备，然后创建并注册spi_device。
static void scan_boardinfo(struct spi_master *master)
        {
                struct boardinfo *bi;
                mutex_lock(&board_lock);
                list_for_each_entry(bi, &board_list, list) {
                        struct spi_board_info *chip = bi->board_info;
                        unsigned n;
                        for (n = bi->n_board_info; n > ; n--, chip++) {
                                if (chip->bus_num != master->bus_num)
                                continue;
                                /* NOTE: this relies on spi_new_device to
                                * issue diagnostics when given bogus inputs
                                */
                                (void) spi_new_device(master, chip);    //创建并注册了spi_device
                        }
                }
                mutex_unlock(&board_lock);
        }
//spi_driver.c linux内核中的/driver/mtd/devices/m25p80.c驱动为参考
static struct spi_driver m25p80_driver = { //spi_driver的构建
                .driver = {
                        .name = "m25p80",
                        .bus = &spi_bus_type,
                        .owner = THIS_MODULE,
                },
                .probe = m25p_probe,
                .remove = __devexit_p(m25p_remove),
                */
        };
spi_register_driver(&m25p80_driver);//spi driver的注册
//在有匹配的spi device时，会调用m25p_probe,根据传入的spi_device参数，可以找到对应的spi_master。接下来就可以利用spi子系统为我们完成数据交互了
static int __devinit m25p_probe(struct spi_device *spi)

Step2，实现SPI platform 总线匹配

　　S3C2440和S5PC100的SPI控制器驱动的实现同样采用了Platform驱动模型，针对S3C2440在drivers/spi/spi_s3c24xx.c中，模块初始化函数s3c24xx_spi_init()完成了platform驱动的注册，名称是“s3c2410-spi”,与该驱动匹配的平台设备在arch/arm/plat-samsung/devs.c中定义，并且与驱动同名，针对S5PC100，详见下面代码,匹配完成后调用相应的probe：

//Platform_device，SPI控制器对应platform_device的定义方式，同样以S5PC100中的SPI控制器为例，参看arch/arm/plat-s5pc1xx/dev-spi.c文件
struct platform_device s3c_device_spi0 = {
                .name = "s3c64xx-spi",     //名称，要和Platform_driver匹配
                .id = ,     //第0个控制器，S5PC100中有3个控制器
                .num_resources = ARRAY_SIZE(s5pc1xx_spi0_resource),    //占用资源的种类
                .resource = s5pc1xx_spi0_resource,    //指向资源结构数组的指针
                .dev = {
                        .dma_mask = &spi_dmamask,     //dma寻址范围
                        .coherent_dma_mask = DMA_BIT_MASK(),     //可以通过关闭cache等措施保证一致性的dma寻址范围
                        .platform_data = &s5pc1xx_spi0_pdata,    //特殊的平台数据，参看后文
                },
        };
static struct s3c64xx_spi_cntrlr_info s5pc1xx_spi0_pdata = {
        .cfg_gpio = s5pc1xx_spi_cfg_gpio,    //用于控制器管脚的IO配置
        .fifo_lvl_mask = 0x7f,
        .rx_lvl_offset = ,
        };
static int s5pc1xx_spi_cfg_gpio(struct platform_device *pdev)
        {
        switch (pdev->id) {
        case :
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB0_SPI_MISO0);
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB1_SPI_CLK0);
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB2_SPI_MOSI0);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                break;
case :
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB4_SPI_MISO1);
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB5_SPI_CLK1);
                s3c_gpio_cfgpin(S5PC1XX_GPB(), S5PC1XX_GPB6_SPI_MOSI1);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPB(), S3C_GPIO_PULL_UP);
                break;
case :
                s3c_gpio_cfgpin(S5PC1XX_GPG3(), S5PC1XX_GPG3_0_SPI_CLK2);
                s3c_gpio_cfgpin(S5PC1XX_GPG3(), S5PC1XX_GPG3_2_SPI_MISO2);
                s3c_gpio_cfgpin(S5PC1XX_GPG3(), S5PC1XX_GPG3_3_SPI_MOSI2);
                s3c_gpio_setpull(S5PC1XX_GPG3(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPG3(), S3C_GPIO_PULL_UP);
                s3c_gpio_setpull(S5PC1XX_GPG3(), S3C_GPIO_PULL_UP);
                break;
default:
                dev_err(&pdev->dev, "Invalid SPI Controller number!");
                return -EINVAL;
        }
//platform_driver，参看drivers/spi/spi_s3c64xx.c文件
static struct platform_driver s3c64xx_spi_driver = {
                .driver = {
                        .name = "s3c64xx-spi", //名称，和platform_device对应
                        .owner = THIS_MODULE,
                },
                .remove = s3c64xx_spi_remove,
                .suspend = s3c64xx_spi_suspend,
                .resume = s3c64xx_spi_resume,
        };
platform_driver_probe(&s3c64xx_spi_driver, s3c64xx_spi_probe)；//注册s3c64xx_spi_driver
//和平台中注册的platform_device匹配后，调用s3c64xx_spi_probe。然后根据传入的platform_device参数，构建一个用于描述SPI控制器的结构体spi_master，并注册。spi_register_master(master)。后续注册的spi_device需要选定自己的spi_master，并利用spi_master提供的传输功能传输spi数据。和I2C类似，SPI也有一个描述控制器的对象叫spi_master,其主要成员是主机控制器的序号（系统中可能存在多个SPI主机控制器）、片选数量、SPI模式和时钟设置用到的函数、数据传输用到的函数等;
struct spi_master {
                struct device    dev;
                s16  bus_num;     //表示是SPI主机控制器的编号。由平台代码决定
                u16  num_chipselect;    //控制器支持的片选数量，即能支持多少个spi设备
                int  (*setup)(struct spi_device *spi);    //针对设备设置SPI的工作时钟及数据传输模式等。在spi_add_device函数中调用。
                int  (*transfer)(struct spi_device *spi,
                struct spi_message *mesg);    //实现数据的双向传输，可能会睡眠
                void       (*cleanup)(struct spi_device *spi);    //注销时调用
        };

static int s3c24xx_spi_probe(struct platform_device *pdev)
{
    struct s3c2410_spi_info *pdata;
    struct s3c24xx_spi *hw;
    struct spi_master *master;
    struct resource *res;
    int err = ;
    master = spi_alloc_master(&pdev->dev, sizeof(struct s3c24xx_spi));//分配SPI控制器结构及驱动私有数据
    if (master == NULL) {
        dev_err(&pdev->dev, "No memory for spi_master\n");
        return -ENOMEM;
    }
    hw = spi_master_get_devdata(master);
    memset(hw, , sizeof(struct s3c24xx_spi));
    hw->master = master;
    hw->pdata = pdata = dev_get_platdata(&pdev->dev);
    hw->dev = &pdev->dev;
    if (pdata == NULL) {
        dev_err(&pdev->dev, "No platform data supplied\n");
        err = -ENOENT;
        goto err_no_pdata;
    }
    platform_set_drvdata(pdev, hw);//将SPI控制器私有数据作为平台设备驱动数据，便于通过相应接口获得
    init_completion(&hw->done);//初始化完成接口
    /* initialise fiq handler */
    s3c24xx_spi_initfiq(hw);
    /* setup the master state. */
    /* the spi->mode bits understood by this driver: */
    master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;
    master->num_chipselect = hw->pdata->num_cs;//设置控制器片选总数和总线编号
    master->bus_num = pdata->bus_num;
    /* setup the state for the bitbang driver 初始化bitbang驱动的相关成员*/
    hw->bitbang.master         = hw->master;
    hw->bitbang.setup_transfer = s3c24xx_spi_setupxfer;
    hw->bitbang.chipselect     = s3c24xx_spi_chipsel;
    hw->bitbang.txrx_bufs      = s3c24xx_spi_txrx;
    hw->master->setup  = s3c24xx_spi_setup;
    hw->master->cleanup = s3c24xx_spi_cleanup;
    dev_dbg(hw->dev, "bitbang at %p\n", &hw->bitbang);
    /* find and map our resources 这是平台驱动中最常规的工作，找到并映射资源*/
    res = platform_get_resource(pdev, IORESOURCE_MEM, );
    hw->regs = devm_ioremap_resource(&pdev->dev, res);
    if (IS_ERR(hw->regs)) {
        err = PTR_ERR(hw->regs);
        goto err_no_pdata;
    }
    hw->irq = platform_get_irq(pdev, );
    if (hw->irq < ) {
        dev_err(&pdev->dev, "No IRQ specified\n");
        err = -ENOENT;
        goto err_no_pdata;
    }
    err = devm_request_irq(&pdev->dev, hw->irq, s3c24xx_spi_irq, ,
                pdev->name, hw);
    if (err) {
        dev_err(&pdev->dev, "Cannot claim IRQ\n");
        goto err_no_pdata;
    }
    hw->clk = devm_clk_get(&pdev->dev, "spi");//获取SPI的时钟资源
    if (IS_ERR(hw->clk)) {
        dev_err(&pdev->dev, "No clock for device\n");
        err = PTR_ERR(hw->clk);
        goto err_no_pdata;
    }
    /* setup any gpio we can 设置片选方法并配置片选引脚 */
    if (!pdata->set_cs) {
        if (pdata->pin_cs < ) {
            dev_err(&pdev->dev, "No chipselect pin\n");
            err = -EINVAL;
            goto err_register;
        }
        err = devm_gpio_request(&pdev->dev, pdata->pin_cs,
                    dev_name(&pdev->dev));
        if (err) {
            dev_err(&pdev->dev, "Failed to get gpio for cs\n");
            goto err_register;
        }
        hw->set_cs = s3c24xx_spi_gpiocs;
        gpio_direction_output(pdata->pin_cs, );
    } else
        hw->set_cs = pdata->set_cs;
    s3c24xx_spi_initialsetup(hw);//使能SPI时钟，初始化2440 SPI控制器寄存器及片选引脚等
    /* register our spi controller 注册SPI控制器，进而完成对控制器对象的分配初始化和注册，注册控制器会扫描
　　　　board_list链表，从中取出spi_board_info创建spi_device设备，因此在执行probe方法时，只要board_list链表
　　　　上有控制器对应的spi_board_info，就能创建出控制器的设备对象，并与控制器设备驱动匹配，进而创建出用于访问该控制器的设备文件
　　*/
    err = spi_bitbang_start(&hw->bitbang);
    if (err) {
        dev_err(&pdev->dev, "Failed to register SPI master\n");
        goto err_register;
    }
    return ;
 err_register:
    clk_disable(hw->clk);
 err_no_pdata:
    spi_master_put(hw->master);
    return err;
}

Step3，分析实现SPI总线通信方法

　　SPI控制器通常由spi_bitbang来完成实际数据的数据传输，spi_bitbang的定义如下：

struct spi_bitbang {
    spinlock_t        lock;   /*操作工作队列时使用的自旋锁*/
    u8            busy;
    u8            use_dma;
    u8            flags;        /* extra spi->mode support */
    struct spi_master    *master;
    /* setup_transfer() changes clock and/or wordsize to match settings
     * for this transfer; zeroes restore defaults from spi_device.为特定的传输设置时钟、字宽等属性的方法
     */
    int    (*setup_transfer)(struct spi_device *spi,
            struct spi_transfer *t);
    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()为实际的传输方法 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_*]()按字传输的方法 just looks like a shift register */
    u32    (*txrx_word[])(struct spi_device *spi,
            unsigned nsecs,
            u32 word, u8 bits);
};

　　两者的SPI总线通信控制方法不同，在上面spi_bitbang结构可以看出，消息传输启动利用的是spi_bibang_txrx_bufs(),在2440 SPI驱动中是通过s3c24xx_spi_txrx()来实现，他将传输段中请求数据的缓冲区和长度赋值给s3c24xx_spi对象的相关成员，然后主动发送一个字节数据，启动传输过程，之后使用进程阻塞在完成接口s3c24xx_spi.done上，其他数据的传输将在中断处理函数中完成，中断检查到发送完成后，通知完成接口，唤醒之前阻塞在其上的进程（这里特别说明下6410SPI通信方法，与2440不同，采用DMA传输，相应的实现函数为s3c64xx_spi_transfer(),利用工作队列进行延迟调度），m25p80SPI总线通信控制详尽代码如下，说明一点，spi_message的消息可以同步传输也可以异步传输，正常产品中基本上都是异步传输，传输结束时有spi_message.complete()方法完成，下面的例子以同步实现简单实现：

#include <linux/platform_device.h>
        #include <linux/spi/spi.h>
        #include <linux/init.h>
        #include <linux/module.h>
        #include <linux/device.h>
        #include <linux/interrupt.h>
        #include <linux/mutex.h>
        #include <linux/slab.h> // kzalloc
        #include <linux/delay.h>
#define FLASH_PAGE_SIZE     256
/* Flash Operating Commands */
        #define CMD_READ_ID                 0x9f
        #define CMD_WRITE_ENABLE    0x06
        #define CMD_BULK_ERASE        0xc7
        #define CMD_READ_BYTES        0x03
        #define CMD_PAGE_PROGRAM    0x02
        #define CMD_RDSR            0x05
/* Status Register bits. */
        #define SR_WIP           1   /* Write in progress */
        #define SR_WEL          2   /* Write enable latch */
/* ID Numbers */
        #define MANUFACTURER_ID     0x20
        #define DEVICE_ID           0x1120
/* Define max times to check status register before we give up. */
        #define MAX_READY_WAIT_COUNT    100000
        #define CMD_SZ  4
struct m25p10a {
                struct spi_device   *spi;
                struct mutex        lock;
                char    erase_opcode;
                char    cmd[ CMD_SZ ];
        };
/*
        * Internal Helper functions
        */
/*
        * Read the status register, returning its value in the location
        * Return the status register value.
        * Returns negative if error occurred.
        */
        static int read_sr(struct m25p10a *flash)
        {
                ssize_t retval;
                u8 code = CMD_RDSR;
                u8 val;
        retval = spi_write_then_read(flash->spi, &code, , &val, );

        if (retval < ) {
                       dev_err(&flash->spi->dev, "error %d reading SR\n", (int) retval);
                       return retval;
                 }
        return val;
        }
/*
        * Service routine to read status register until ready, or timeout occurs.
        * Returns non-zero if error.
        */
        static int wait_till_ready(struct m25p10a *flash)
        {
                int count;
                int sr;
        /* one chip guarantees max 5 msec wait here after page writes,
                * but potentially three seconds (!) after page erase.
                */
                for (count = ; count < MAX_READY_WAIT_COUNT; count++) {
                        if ((sr = read_sr(flash)) < )
                                break;
                        else if (!(sr & SR_WIP))
                                return ;
                /* REVISIT sometimes sleeping would be best */
                }
                 printk( "in (%s): count = %d\n", count );
        return ;
        }
/*
        * Set write enable latch with Write Enable command.
        * Returns negative if error occurred.
        */
        static inline int write_enable( struct m25p10a *flash )
        {
                flash->cmd[] = CMD_WRITE_ENABLE;
                return spi_write( flash->spi, flash->cmd,  );
        }
/*
        * Erase the whole flash memory
        *
        * Returns 0 if successful, non-zero otherwise.
        */
        static int erase_chip( struct m25p10a *flash )
        {
                /* Wait until finished previous write command. */
                if (wait_till_ready(flash))
                        return -;

        /* Send write enable, then erase commands. */
                write_enable( flash );
                flash->cmd[] = CMD_BULK_ERASE;
                return spi_write( flash->spi, flash->cmd,  );
        }
/*
        * Read an address range from the flash chip.  The address range
        * may be any size provided it is within the physical boundaries.
        */
        static int m25p10a_read( struct m25p10a *flash, loff_t from,  size_t len, char *buf )
        {
                int r_count = , i;

        flash->cmd[] = CMD_READ_BYTES;
                flash->cmd[] = from >> ;
                flash->cmd[] = from >> ;
                flash->cmd[] = from;

        #if 1
                struct spi_transfer st[];
                struct spi_message  msg;

                spi_message_init( &msg );
                memset( st, , sizeof(st) );

        flash->cmd[] = CMD_READ_BYTES;
                flash->cmd[] = from >> ;
                flash->cmd[] = from >> ;
                flash->cmd[] = from;

        st[  ].tx_buf = flash->cmd;
                st[  ].len = CMD_SZ;
                spi_message_add_tail( &st[], &msg );

        st[  ].rx_buf = buf;
                st[  ].len = len;
                spi_message_add_tail( &st[], &msg );

        mutex_lock( &flash->lock );

                /* Wait until finished previous write command. */
                if (wait_till_ready(flash)) {
                        mutex_unlock( &flash->lock );
                        return -;
                }

        spi_sync( flash->spi, &msg );
                r_count = msg.actual_length - CMD_SZ;
                printk( "in (%s): read %d bytes\n", __func__, r_count );
                for( i = ; i < r_count; i++ ) {
                        printk( "0x%02x\n", buf[ i ] );
                }
        mutex_unlock( &flash->lock );
        #endif

        return ;
        }
/*
        * Write an address range to the flash chip.  Data must be written in
        * FLASH_PAGE_SIZE chunks.  The address range may be any size provided
        * it is within the physical boundaries.
        */
        static int m25p10a_write( struct m25p10a *flash, loff_t to, size_t len, const char *buf )
        {
                int w_count = , i, page_offset;
                struct spi_transfer st[];
                struct spi_message  msg;
        #if 1
                if (wait_till_ready(flash)) {    //读状态，等待ready
                mutex_unlock( &flash->lock );
                return -;
                }
        #endif
                write_enable( flash );  //写使能 

                spi_message_init( &msg );
                memset( st, , sizeof(st) );

        flash->cmd[] = CMD_PAGE_PROGRAM;
                flash->cmd[] = to >> ;
                flash->cmd[] = to >> ;
                flash->cmd[] = to;

        st[  ].tx_buf = flash->cmd;
                st[  ].len = CMD_SZ;
                spi_message_add_tail( &st[], &msg );

        st[  ].tx_buf = buf;
                st[  ].len = len;
                spi_message_add_tail( &st[], &msg );

        mutex_lock( &flash->lock );

        /* get offset address inside a page */
                page_offset = to % FLASH_PAGE_SIZE;    

        /* do all the bytes fit onto one page? */
                if( page_offset + len <= FLASH_PAGE_SIZE ) {    // yes
                        st[  ].len = len;
                        printk("%d, cmd = %d\n", st[  ].len, *(char *)st[].tx_buf);
                        //while(1)
                        {
                        spi_sync( flash->spi, &msg );
                        }
                        w_count = msg.actual_length - CMD_SZ;
                }
                else {  // no
                }
                printk( "in (%s): write %d bytes to flash in total\n", __func__, w_count );
                mutex_unlock( &flash->lock );
                return ;
        }

static int check_id( struct m25p10a *flash )
        {
                char buf[] = {};
                flash->cmd[] = CMD_READ_ID;
                spi_write_then_read( flash->spi, flash->cmd, , buf,  );
                printk( "Manufacture ID: 0x%x\n", buf[] );
                printk( "Device ID: 0x%x\n", buf[] | buf[]  <<  );
                return buf[] <<  | buf[] <<  | buf[];
        }
static int m25p10a_probe(struct spi_device *spi)
        {
                int ret = ;
                struct m25p10a  *flash;
                char buf[  ];
                printk( "%s was called\n", __func__ );
                flash = kzalloc( sizeof(struct m25p10a), GFP_KERNEL );
                if( !flash ) {
                        return -ENOMEM;
                }
                flash->spi = spi;
                mutex_init( &flash->lock );
                /* save flash as driver's private data */
                spi_set_drvdata( spi, flash );

                check_id( flash );    //读取ID
        #if 1
                ret = erase_chip( flash );  //擦除
                if( ret <  ) {
                        printk( "erase the entirely chip failed\n" );
                }
                printk( "erase the whole chip done\n" );
                memset( buf, 0x7,  );
                m25p10a_write( flash, , , buf); //0地址写入20个7
                memset( buf, ,  );
                m25p10a_read( flash, , , buf ); //0地址读出25个数
        #endif
                return ;
        }
static int m25p10a_remove(struct spi_device *spi)
        {
                return ;
        }
static struct spi_driver m25p10a_driver = {
                .probe = m25p10a_probe,
                .remove = m25p10a_remove,
                .driver = {
                        .name = "m25p10a",
                },
        };
static int __init m25p10a_init(void)
        {
                return spi_register_driver(&m25p10a_driver);
        }
static void __exit m25p10a_exit(void)
        {
                spi_unregister_driver(&m25p10a_driver);
        }
module_init(m25p10a_init);
        module_exit(m25p10a_exit);
MODULE_DESCRIPTION("m25p10a driver for FS_S5PC100");
MODULE_LICENSE("GPL");

参考文献 1.《深入Linux内核架构》 2.《Linux设备驱动开发详解》