I2C自编设备驱动设计

一、自编设备驱动模型

at24.c:

static int __init at24_init(void)
{
    io_limit = rounddown_pow_of_two(io_limit);
    return i2c_add_driver(&at24_driver);                                   //注册i2c驱动设备
}

at24_driver:

static struct i2c_driver at24_driver = {
    .driver = {
        .name = "at24",
        .owner = THIS_MODULE,
    },
    .probe = at24_probe,                                                  //找到驱动对应的设备调用的函数
    .remove = __devexit_p(at24_remove),
    .id_table = at24_ids,                                                 //这个表里的设备都支持
};

at24_probe:

static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
    struct at24_platform_data chip;
    bool writable;
    bool use_smbus = false;
    struct at24_data *at24;
    int err;
    unsigned i, num_addresses;
    kernel_ulong_t magic;

    if (client->dev.platform_data) {
        chip = *(struct at24_platform_data *)client->dev.platform_data;
    } else {
        if (!id->driver_data) {
            err = -ENODEV;
            goto err_out;
        }
        magic = id->driver_data;
        chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
        magic >>= AT24_SIZE_BYTELEN;
        chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
        /*
         * This is slow, but we can't know all eeproms, so we better
         * play safe. Specifying custom eeprom-types via platform_data
         * is recommended anyhow.
         */
        chip.page_size = 1;

        chip.setup = NULL;
        chip.context = NULL;
    }

    if (!is_power_of_2(chip.byte_len))
        dev_warn(&client->dev,
            "byte_len looks suspicious (no power of 2)!\n");
    if (!is_power_of_2(chip.page_size))
        dev_warn(&client->dev,
            "page_size looks suspicious (no power of 2)!\n");

    /* Use I2C operations unless we're stuck with SMBus extensions. */
    if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
        if (chip.flags & AT24_FLAG_ADDR16) {
            err = -EPFNOSUPPORT;
            goto err_out;
        }
        if (!i2c_check_functionality(client->adapter,
                I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
            err = -EPFNOSUPPORT;
            goto err_out;
        }
        use_smbus = true;
    }

    if (chip.flags & AT24_FLAG_TAKE8ADDR)
        num_addresses = 8;
    else
        num_addresses =    DIV_ROUND_UP(chip.byte_len,
            (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);

    at24 = kzalloc(sizeof(struct at24_data) +
        num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
    if (!at24) {
        err = -ENOMEM;
        goto err_out;
    }

    mutex_init(&at24->lock);
    at24->use_smbus = use_smbus;
    at24->chip = chip;
    at24->num_addresses = num_addresses;

    /*
     * Export the EEPROM bytes through sysfs, since that's convenient.
     * By default, only root should see the data (maybe passwords etc)
     */
    at24->bin.attr.name = "eeprom";
    at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
    at24->bin.read = at24_bin_read;
    at24->bin.size = chip.byte_len;

    at24->macc.read = at24_macc_read;

    writable = !(chip.flags & AT24_FLAG_READONLY);
    if (writable) {
        if (!use_smbus || i2c_check_functionality(client->adapter,
                I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {

            unsigned write_max = chip.page_size;

            at24->macc.write = at24_macc_write;

            at24->bin.write = at24_bin_write;                          //这里注册了at24_bin_write，用户的write函数的调用接口
            at24->bin.attr.mode |= S_IWUSR;

            if (write_max > io_limit)
                write_max = io_limit;
            if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
                write_max = I2C_SMBUS_BLOCK_MAX;
            at24->write_max = write_max;

            /* buffer (data + address at the beginning) */
            at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
            if (!at24->writebuf) {
                err = -ENOMEM;
                goto err_struct;
            }
        } else {
            dev_warn(&client->dev,
                "cannot write due to controller restrictions.");
        }
    }

    at24->client[0] = client;

    /* use dummy devices for multiple-address chips */
    for (i = 1; i < num_addresses; i++) {
        at24->client[i] = i2c_new_dummy(client->adapter,
                    client->addr + i);
        if (!at24->client[i]) {
            dev_err(&client->dev, "address 0x%02x unavailable\n",
                    client->addr + i);
            err = -EADDRINUSE;
            goto err_clients;
        }
    }

    err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);          //创建一个文件应用程序实际上是在/sys目录下的文件，而这个文件就是它函数创建的。
    if (err)
        goto err_clients;

    i2c_set_clientdata(client, at24);

    dev_info(&client->dev, "%zu byte %s EEPROM %s\n",
        at24->bin.size, client->name,
        writable ? "(writable)" : "(read-only)");
    dev_dbg(&client->dev,
        "page_size %d, num_addresses %d, write_max %d%s\n",
        chip.page_size, num_addresses,
        at24->write_max,
        use_smbus ? ", use_smbus" : "");

    /* export data to kernel code */
    if (chip.setup)
        chip.setup(&at24->macc, chip.context);

    return 0;

err_clients:
    for (i = 1; i < num_addresses; i++)
        if (at24->client[i])
            i2c_unregister_device(at24->client[i]);

    kfree(at24->writebuf);
err_struct:
    kfree(at24);
err_out:
    dev_dbg(&client->dev, "probe error %d\n", err);
    return err;
}

at24_bin_write:

static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
        char *buf, loff_t off, size_t count)
{
    struct at24_data *at24;

    at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
    return at24_write(at24, buf, off, count);                        //调用at24_write
}

at24_write:

static ssize_t at24_write(struct at24_data *at24, const char *buf, loff_t off,
              size_t count)
{
    ssize_t retval = 0;

    if (unlikely(!count))
        return count;

    mutex_lock(&at24->lock);

    while (count) {
        ssize_t    status;

        status = at24_eeprom_write(at24, buf, off, count);                    //调用at24_eeprom_write
        if (status <= 0) {
            if (retval == 0)
                retval = status;
            break;
        }
        buf += status;
        off += status;
        count -= status;
        retval += status;
    }

    mutex_unlock(&at24->lock);

    return retval;
}

at24_eeprom_write:

static ssize_t at24_eeprom_write(struct at24_data *at24, const char *buf,
        unsigned offset, size_t count)
{
    struct i2c_client *client;
    struct i2c_msg msg;
    ssize_t status;
    unsigned long timeout, write_time;
    unsigned next_page;

    /* Get corresponding I2C address and adjust offset */
    client = at24_translate_offset(at24, &offset);

    /* write_max is at most a page */
    if (count > at24->write_max)
        count = at24->write_max;

    /* Never roll over backwards, to the start of this page */
    next_page = roundup(offset + 1, at24->chip.page_size);
    if (offset + count > next_page)
        count = next_page - offset;

    /* If we'll use I2C calls for I/O, set up the message */                     //I2C的消息
    if (!at24->use_smbus) {
        int i = 0;

        msg.addr = client->addr;
        msg.flags = 0;

        /* msg.buf is u8 and casts will mask the values */
        msg.buf = at24->writebuf;
        if (at24->chip.flags & AT24_FLAG_ADDR16)
            msg.buf[i++] = offset >> 8;

        msg.buf[i++] = offset;                                          //提供偏移地址
        memcpy(&msg.buf[i], buf, count);                                //拷贝用户发送数据
        msg.len = i + count;                                            //设置长度
    }

    /*
     * Writes fail if the previous one didn't complete yet. We may
     * loop a few times until this one succeeds, waiting at least
     * long enough for one entire page write to work.
     */
    timeout = jiffies + msecs_to_jiffies(write_timeout);
    do {
        write_time = jiffies;
        if (at24->use_smbus) {
            status = i2c_smbus_write_i2c_block_data(client,
                    offset, count, buf);
            if (status == 0)
                status = count;
        } else {
            status = i2c_transfer(client->adapter, &msg, 1);                     //交给I2C控制器完成
            if (status == 1)
                status = count;
        }
        dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
                count, offset, status, jiffies);

        if (status == count)
            return count;

        /* REVISIT: at HZ=100, this is sloooow */
        msleep(1);
    } while (time_before(write_time, timeout));

    return -ETIMEDOUT;
}

i2c_transfer:

int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
    int ret;

    if (adap->algo->master_xfer) {
#ifdef DEBUG
        for (ret = 0; ret < num; ret++) {
            dev_dbg(&adap->dev, "master_xfer[%d] %c, addr=0x%02x, "
                "len=%d%s\n", ret, (msgs[ret].flags & I2C_M_RD)
                ? 'R' : 'W', msgs[ret].addr, msgs[ret].len,
                (msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
        }
#endif

        if (in_atomic() || irqs_disabled()) {
            ret = mutex_trylock(&adap->bus_lock);
            if (!ret)
                /* I2C activity is ongoing. */
                return -EAGAIN;
        } else {
            mutex_lock_nested(&adap->bus_lock, adap->level);
        }

        ret = adap->algo->master_xfer(adap,msgs,num);                   //调用控制器中的算法
        mutex_unlock(&adap->bus_lock);

        return ret;
    } else {
        dev_dbg(&adap->dev, "I2C level transfers not supported\n");
        return -EOPNOTSUPP;
    }
}

然后看一下i2c_bin_read:

static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
        char *buf, loff_t off, size_t count)
{
    struct at24_data *at24;

    at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
    return at24_read(at24, buf, off, count);                               //调用at24_read
}

at24_read:

static ssize_t at24_read(struct at24_data *at24,
        char *buf, loff_t off, size_t count)
{
    ssize_t retval = 0;

    if (unlikely(!count))
        return count;

    mutex_lock(&at24->lock);

    while (count) {
        ssize_t    status;

        status = at24_eeprom_read(at24, buf, off, count);                  //继续调用at24_eeprom_read
        if (status <= 0) {
            if (retval == 0)
                retval = status;
            break;
        }
        buf += status;
        off += status;
        count -= status;
        retval += status;
    }

    mutex_unlock(&at24->lock);

    return retval;
}

at24_eeprom_read:

static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
        unsigned offset, size_t count)
{
    struct i2c_msg msg[2];
    u8 msgbuf[2];
    struct i2c_client *client;
    int status, i;

    memset(msg, 0, sizeof(msg));

    client = at24_translate_offset(at24, &offset);

    if (count > io_limit)
        count = io_limit;

    /* Smaller eeproms can work given some SMBus extension calls */
    if (at24->use_smbus) {
        if (count > I2C_SMBUS_BLOCK_MAX)
            count = I2C_SMBUS_BLOCK_MAX;
        status = i2c_smbus_read_i2c_block_data(client, offset,
                count, buf);
        dev_dbg(&client->dev, "smbus read %zu@%d --> %d\n",
                count, offset, status);
        return (status < 0) ? -EIO : status;
    }

    i = 0;
    if (at24->chip.flags & AT24_FLAG_ADDR16)
        msgbuf[i++] = offset >> 8;
    msgbuf[i++] = offset;                                                //设置偏移

    msg[0].addr = client->addr;                                          //第一条消息，提供从设备地址
    msg[0].buf = msgbuf;
    msg[0].len = i;

    msg[1].addr = client->addr;                                          //第二条消息
    msg[1].flags = I2C_M_RD;                                             //flags是读
    msg[1].buf = buf;                                                    //提供数据量
    msg[1].len = count;

    status = i2c_transfer(client->adapter, msg, 2);
    dev_dbg(&client->dev, "i2c read %zu@%d --> %d\n",
            count, offset, status);

    if (status == 2)
        return count;
    else if (status >= 0)
        return -EIO;
    else
        return status;
}

二、对驱动程序的修改和移植
I2C设备的注册：

static void __init tq2440_machine_init(void)
{
    s3c24xx_fb_set_platdata(&tq2440_fb_info);
    s3c_i2c0_set_platdata(NULL);

    platform_add_devices(tq2440_devices, ARRAY_SIZE(tq2440_devices));
    EmbedSky_machine_init();
    s3c2410_gpio_setpin(S3C2410_GPG12, 0);
    s3c2410_gpio_cfgpin(S3C2410_GPG12, S3C2410_GPIO_OUTPUT);
    s3c24xx_udc_set_platdata(&EmbedSky_udc_cfg);
}

增加设备：

static struct at24_platform_data at24c02 = {
    .byte_len = 2048 / 8,
    .page_size = 8,
    .flags = 0,
};

static struct i2c_board_info __initdata tq2440_i2c_devices[] = {
    {
        I2C_BOARD_INFO("24c02", 0x50),
        .platform_data = &at24c02,
    },
};

然后在tq2440_machine_init中添加：

i2c_register_board_info(0, tq2440_i2c_devices, ARRAY_SIZE(tq2440_i2c_devices));

然后添加头文件：

#include <linux/i2c.h>
#include <linux/i2c/at24.h>

然后会在开发板/sys/bus/i2c/devices/有一个0-0050的目录，有一个eeprom文件。

编写i2c-app.c文件：

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main()
{
    char write_data[256],read_data[256];
    int fd;
    int i = 0;
    //打开at24c02对应的sys文件
    fd = open("/sys/bus/i2c/devices/0-0050/eeprom", O_RDWR);

    //写入数据
    for(i=0;i<256;i++)
        write_data[i] = i;

    lseek(fd, 0, SEEK_SET);
    write(fd, write_data, 256);
    //读出数据
    lseek(fd, 0, SEEK_SET);
    read(fd, read_data, 256);

    //打印对比
    for(i=0;i<256;i++)
    {
        if(i%16 == 0) printf("\r\n");
        printf("%3d ",read_data[i]);
    }
    printf("\n");
    close(fd);
}