linux的I2C驱动——移植篇

**

一、简介

**
1、I2C是一个一主多从的通信协议，通信都是由主设备发起的。
SCL : 时钟线，由主端控制；
SDA：数据线，主端和从端都可以配置；
SCL和SDA的默认电平状态是高。
2、通信协议
Start信号: SCL保持高电平，SDA从高到低跳变；
Stop信号: SCL保持高电平，SDA从低到高跳变；
Ack信号 : 表示是否处于数据交互状态。
3、通信过程
主设备发送Start信号；
主设备发送从地址；
主设备发送读写命令；
从设备返回Ack信号；
主设备写/读数据；
主设备发送Stop信号。

二、 代码修改

    在进行I2C设备驱动移植的时候，我们只需关心i2c_driver与i2c_client这两个结构体。
    1、i2c_client
    i2c_client的分配、初始化、注册都是由内核实现的，我们只需要对i2c_board_info进行配置初始化即可，内核会根据i2c_board_info去填充i2c_client的。
    开发板文件一般位于arch/arm/mach-xxx/mach-xxx.c

static struct i2c_board_info at24xx[]={
    {
        I2C_BOARD_INFO("at2402",x050);
    },
};
i2c_register_board_info(0,at24xx,ARRAY_SIZE(at24xx));

源码为3.0以后的代码可以用以下的方法：
修改设备树文件，一般位于arch/arm/boot/dts/xxx.dts

i2c@11000{
        status = "okay";
        ……
        eeprom@50{
                compatible = "atmel,24c02";
                reg = <0x50>;
        };
};

2、i2c_driver

const struct i2c_device_id at24cxx_id[] =
{
        {"at24c02",0},
        {}
};
MODULE_DEVICE_TABLE(i2c,at24cxx_id);

用于驱动和设备的匹配。

struct i2c_driver at24cxx_driver = 
{
    .driver = 
    {
        .name = "at24c02",
        .owner = THIS_MODULE,
    },
    .probe = at24cxx_probe,
    .remove = at24cxx_remove,
    //匹配使用
    .id_table = at24cxx_id,
};

用于驱动的初始化

struct file_operations at24cxx_fops = 
{
    .owner = THIS_MODULE,
    .read = at24_read,
    .write = at24_write,
};

用于上层操作的API。
按照驱动的时序，完善以上的函数，就可以完成驱动的移植了。详细代码路径：driver/misc/eeprom/at24.c，以下为部分代码片段

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;
    unsigned long timeout, read_time;
    int status, i;

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

    /*
     * REVISIT some multi-address chips don't rollover page reads to
     * the next slave address, so we may need to truncate the count.
     * Those chips might need another quirk flag.
     *
     * If the real hardware used four adjacent 24c02 chips and that
     * were misconfigured as one 24c08, that would be a similar effect:
     * one "eeprom" file not four, but larger reads would fail when
     * they crossed certain pages.
     */

    /*
     * Slave address and byte offset derive from the offset. Always
     * set the byte address; on a multi-master board, another master
     * may have changed the chip's "current" address pointer.
     */
    client = at24_translate_offset(at24, &offset);

    if (count > io_limit)
        count = io_limit;

    switch (at24->use_smbus) {
    case I2C_SMBUS_I2C_BLOCK_DATA:
        /* Smaller eeproms can work given some SMBus extension calls */
        if (count > I2C_SMBUS_BLOCK_MAX)
            count = I2C_SMBUS_BLOCK_MAX;
        break;
    case I2C_SMBUS_WORD_DATA:
        count = 2;
        break;
    case I2C_SMBUS_BYTE_DATA:
        count = 1;
        break;
    default:
        /*
         * When we have a better choice than SMBus calls, use a
         * combined I2C message. Write address; then read up to
         * io_limit data bytes. Note that read page rollover helps us
         * here (unlike writes). msgbuf is u8 and will cast to our
         * needs.
         */
        i = 0;
        if (at24->chip.flags & AT24_FLAG_ADDR16)
            msgbuf[i++] = offset >> 8;
        msgbuf[i++] = offset;

        msg[0].addr = client->addr;
        msg[0].buf = msgbuf;
        msg[0].len = i;

        msg[1].addr = client->addr;
        msg[1].flags = I2C_M_RD;
        msg[1].buf = buf;
        msg[1].len = count;
    }

    /*
     * Reads fail if the previous write 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 {
        read_time = jiffies;
        switch (at24->use_smbus) {
        case I2C_SMBUS_I2C_BLOCK_DATA:
            status = i2c_smbus_read_i2c_block_data(client, offset,
                    count, buf);
            break;
        case I2C_SMBUS_WORD_DATA:
            status = i2c_smbus_read_word_data(client, offset);
            if (status >= 0) {
                buf[0] = status & 0xff;
                buf[1] = status >> 8;
                status = count;
            }
            break;
        case I2C_SMBUS_BYTE_DATA:
            status = i2c_smbus_read_byte_data(client, offset);
            if (status >= 0) {
                buf[0] = status;
                status = count;
            }
            break;
        default:
            status = i2c_transfer(client->adapter, msg, 2);
            if (status == 2)
                status = count;
        }
        dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
                count, offset, status, jiffies);

        if (status == count)
            return count;

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

    return -ETIMEDOUT;
}

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;

    /*
     * Read data from chip, protecting against concurrent updates
     * from this host, but not from other I2C masters.
     */
    mutex_lock(&at24->lock);

    while (count) {
        ssize_t status;

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

    mutex_unlock(&at24->lock);

    return retval;
}
/*
 * Note that if the hardware write-protect pin is pulled high, the whole
 * chip is normally write protected. But there are plenty of product
 * variants here, including OTP fuses and partial chip protect.
 *
 * We only use page mode writes; the alternative is sloooow. This routine
 * writes at most one page.
 */
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 */
    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;
        memcpy(&msg.buf[i], buf, count);
        msg.len = i + count;
    }

    /*
     * 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);
            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;
}

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;

    /*
     * Write data to chip, protecting against concurrent updates
     * from this host, but not from other I2C masters.
     */
    mutex_lock(&at24->lock);

    while (count) {
        ssize_t status;

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

    mutex_unlock(&at24->lock);

    return retval;
}

static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
    struct at24_platform_data chip;
    bool writable;
    int use_smbus = 0;
    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;

        /* update chipdata if OF is present */
        at24_get_ofdata(client, &chip);

        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 (!chip.page_size) {
        dev_err(&client->dev, "page_size must not be 0!\n");
        err = -EINVAL;
        goto err_out;
    }
    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)) {
            use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
        } else if (i2c_check_functionality(client->adapter,
                I2C_FUNC_SMBUS_READ_WORD_DATA)) {
            use_smbus = I2C_SMBUS_WORD_DATA;
        } else if (i2c_check_functionality(client->adapter,
                I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
            use_smbus = I2C_SMBUS_BYTE_DATA;
        } else {
            err = -EPFNOSUPPORT;
            goto err_out;
        }
    }

    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)
     */
    sysfs_bin_attr_init(&at24->bin);
    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;
            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);
    if (err)
        goto err_clients;

    i2c_set_clientdata(client, at24);

    dev_info(&client->dev, "%zu byte %s EEPROM, %s, %u bytes/write\n",
        at24->bin.size, client->name,
        writable ? "writable" : "read-only", at24->write_max);
    if (use_smbus == I2C_SMBUS_WORD_DATA ||
        use_smbus == I2C_SMBUS_BYTE_DATA) {
        dev_notice(&client->dev, "Falling back to %s reads, "
               "performance will suffer\n", use_smbus ==
               I2C_SMBUS_WORD_DATA ? "word" : "byte");
    }

    /* 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;
}

static int __devexit at24_remove(struct i2c_client *client)
{
    struct at24_data *at24;
    int i;

    at24 = i2c_get_clientdata(client);
    sysfs_remove_bin_file(&client->dev.kobj, &at24->bin);

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

    kfree(at24->writebuf);
    kfree(at24);
    return 0;
}

/*-------------------------------------------------------------------------*/

static struct i2c_driver at24_driver = {
    .driver = {
        .name = "at24",
        .owner = THIS_MODULE,
    },
    .probe = at24_probe,
    .remove = __devexit_p(at24_remove),
    .id_table = at24_ids,
};

static int __init at24_init(void)
{
    if (!io_limit) {
        pr_err("at24: io_limit must not be 0!\n");
        return -EINVAL;
    }

    io_limit = rounddown_pow_of_two(io_limit);
    return i2c_add_driver(&at24_driver);
}
module_init(at24_init);

static void __exit at24_exit(void)
{
    i2c_del_driver(&at24_driver);
}
module_exit(at24_exit);

MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
MODULE_AUTHOR("David Brownell and Wolfram Sang");
MODULE_LICENSE("GPL");