linux的I2C驱动——移植篇

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一、简介

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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");