Linux I2C驱动完全分析（二）

原文地址： 作者：

2011-05-01 18:17 1820人阅读 评论(8) 举报

博主按：大热的天，刚刚负重从五道口走到石板房，大约4公里吧。终于让我找了一个咖啡屋休息一下，继续写这篇驱动分析。单身的生活就是这样无聊啊。 不发牢骚了，活出个样儿来给自己看！千难万险脚下踩，啥也难不倒咱！继续整！~

先说一下，本文中有个疑惑，一直没有搞懂，写在这里，望高人指点一二，不胜感激！

#define I2C_M_NOSTART  0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK  0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */

这里I2C_FUNC_PROTOCOL_MANGLING 是什么意思？为什么定义这些东东？看了注释也不太理解。求解释！

3. I2C总线驱动代码分析

   s3c2440的总线驱动代码在i2c-s3c2410.c中。照例先从init看起。

static int __init i2c_adap_s3c_init(void)
{
    return platform_driver_register(&s3c24xx_i2c_driver);
}

static int __init i2c_adap_s3c_init(void) { return platform_driver_register(&s3c24xx_i2c_driver); }

在init中只是调用了平台驱动注册函数注册了一个i2c的平台驱动s3c24xx_i2c_driver。这个驱动是一个platform_driver的结构体变量。注意这里不是i2c_driver结构体，因为i2c_driver是对设备的驱动，而这里对控制器的驱动要使用platform_driver

static struct platform_driver s3c24xx_i2c_driver = {
    .probe      = s3c24xx_i2c_probe,
    .remove     = s3c24xx_i2c_remove,
    .suspend_late   = s3c24xx_i2c_suspend_late,
    .resume     = s3c24xx_i2c_resume,
    .id_table   = s3c24xx_driver_ids,
    .driver     = {
        .owner  = THIS_MODULE,
        .name   = "s3c-i2c",
    },
};

static struct platform_driver s3c24xx_i2c_driver = { .probe = s3c24xx_i2c_probe, .remove = s3c24xx_i2c_remove, .suspend_late = s3c24xx_i2c_suspend_late, .resume = s3c24xx_i2c_resume, .id_table = s3c24xx_driver_ids, .driver = { .owner = THIS_MODULE, .name = "s3c-i2c", }, };

同样的，重要的函数还是那几个：probe，remove，suspend_late，resume。再加上一个id_table和device_driver结构体变量。

下面逐个分析：

* probe函数

当调用platform_driver_register函数注册platform_driver结构体时，probe指针指向的s3c24xx_i2c_probe函数将会被调用。这部分详细解释参考本博客另一篇文章《S3C2410看门狗驱动分析》。细心的朋友可能会发现，在s3c24xx_i2c_driver中，驱动的名字是"s3c-i2c"，而在板文件中可以看到，设备的名字是"s3c2410-i2c"，这两个名字不一样，那驱动和设备是如何match的呢？答案就在于id_table。这个id_table包含了驱动所支持的设备ID表。在match的时候，判断这个表中的名字是不是和设备一致，一致则match成功。这也是为什么一个驱动可以同时match成功多个设备的原因。如果只是靠platform_driver-->driver中的名字来匹配的话，那么驱动和设备只能是一对一的关系了。

static struct platform_device_id s3c24xx_driver_ids[] = {
    {
        .name       = "s3c2410-i2c",
        .driver_data    = TYPE_S3C2410,
    }, {
        .name       = "s3c2440-i2c",
        .driver_data    = TYPE_S3C2440,
    }, { },
};

static struct platform_device_id s3c24xx_driver_ids[] = { { .name = "s3c2410-i2c", .driver_data = TYPE_S3C2410, }, { .name = "s3c2440-i2c", .driver_data = TYPE_S3C2440, }, { }, };

扯远了，还是看看probe的代码吧~

static int s3c24xx_i2c_probe(struct platform_device *pdev)
{
    struct s3c24xx_i2c *i2c;
    struct s3c2410_platform_i2c *pdata;
    struct resource *res;
    int ret;

    pdata = pdev->dev.platform_data;
    if (!pdata) {
        dev_err(&pdev->dev, "no platform data/n");
        return -EINVAL;
    }
        //给s3c24xx_i2c结构体申请空间
    i2c = kzalloc(sizeof(struct s3c24xx_i2c), GFP_KERNEL);
    if (!i2c) {
        dev_err(&pdev->dev, "no memory for state/n");
        return -ENOMEM;
    }
        //填充s3c24xx_i2c结构体中各项，包括名称、所有者、算法、所属class等等
    strlcpy(i2c->adap.name, "s3c2410-i2c", sizeof(i2c->adap.name));
    i2c->adap.owner   = THIS_MODULE;
    i2c->adap.algo    = &s3c24xx_i2c_algorithm; //这个下面会重点介绍
    i2c->adap.retries = 2;
    i2c->adap.class   = I2C_CLASS_HWMON | I2C_CLASS_SPD;
    i2c->tx_setup     = 50;

    spin_lock_init(&i2c->lock);
    init_waitqueue_head(&i2c->wait);

    /* find the clock and enable it */
        // 找到i2c始终并且使能它
    i2c->dev = &pdev->dev;
    i2c->clk = clk_get(&pdev->dev, "i2c");
    if (IS_ERR(i2c->clk)) {
        dev_err(&pdev->dev, "cannot get clock/n");
        ret = -ENOENT;
        goto err_noclk;
    }

    dev_dbg(&pdev->dev, "clock source %p/n", i2c->clk);

    clk_enable(i2c->clk);

    /* map the registers */
        /*映射寄存器*/
    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (res == NULL) {
        dev_err(&pdev->dev, "cannot find IO resource/n");
        ret = -ENOENT;
        goto err_clk;
    }

    i2c->ioarea = request_mem_region(res->start, resource_size(res),
                     pdev->name);

    if (i2c->ioarea == NULL) {
        dev_err(&pdev->dev, "cannot request IO/n");
        ret = -ENXIO;
        goto err_clk;
    }

    i2c->regs = ioremap(res->start, resource_size(res));

    if (i2c->regs == NULL) {
        dev_err(&pdev->dev, "cannot map IO/n");
        ret = -ENXIO;
        goto err_ioarea;
    }

    dev_dbg(&pdev->dev, "registers %p (%p, %p)/n",
        i2c->regs, i2c->ioarea, res);

    /* setup info block for the i2c core */

    i2c->adap.algo_data = i2c;
    i2c->adap.dev.parent = &pdev->dev;

    /* initialise the i2c controller */
        /*s3c24xx_i2c结构体变量i2c的必要的信息都填充完了以后，开始进行初始化*/
    ret = s3c24xx_i2c_init(i2c);
    if (ret != 0)
        goto err_iomap;

    /* find the IRQ for this unit (note, this relies on the init call to
     * ensure no current IRQs pending
     */
        //接下来申请中断
    i2c->irq = ret = platform_get_irq(pdev, 0);
    if (ret <= 0) {
        dev_err(&pdev->dev, "cannot find IRQ/n");
        goto err_iomap;
    }

    ret = request_irq(i2c->irq, s3c24xx_i2c_irq, IRQF_DISABLED,
              dev_name(&pdev->dev), i2c);

    if (ret != 0) {
        dev_err(&pdev->dev, "cannot claim IRQ %d/n", i2c->irq);
        goto err_iomap;
    }

    ret = s3c24xx_i2c_register_cpufreq(i2c);
    if (ret < 0) {
        dev_err(&pdev->dev, "failed to register cpufreq notifier/n");
        goto err_irq;
    }

    /* Note, previous versions of the driver used i2c_add_adapter()
     * to add the bus at any number. We now pass the bus number via
     * the platform data, so if unset it will now default to always
     * being bus 0.
     */

    i2c->adap.nr = pdata->bus_num;

        //看到了吧？下面调用了i2c-core中的i2c_add_adapter函数来添加一个i2c控制器
          //i2c_add_numbered_adapter和i2c_add_adapter的区别在于前者用来添加一个在CPU内
          //部集成的适配器，而后者用来添加一个CPU外部的适配器。显然这里应该用前者。
    ret = i2c_add_numbered_adapter(&i2c->adap);
    if (ret < 0) {
        dev_err(&pdev->dev, "failed to add bus to i2c core/n");
        goto err_cpufreq;
    }

    platform_set_drvdata(pdev, i2c);

    dev_info(&pdev->dev, "%s: S3C I2C adapter/n", dev_name(&i2c->adap.dev));
    return 0;

err_cpufreq:
    s3c24xx_i2c_deregister_cpufreq(i2c);

err_irq:
    free_irq(i2c->irq, i2c);

err_iomap:
    iounmap(i2c->regs);

err_ioarea:
    release_resource(i2c->ioarea);
    kfree(i2c->ioarea);

err_clk:
    clk_disable(i2c->clk);
    clk_put(i2c->clk);

err_noclk:
    kfree(i2c);
    return ret;
}

static int s3c24xx_i2c_probe(struct platform_device *pdev) { struct s3c24xx_i2c *i2c; struct s3c2410_platform_i2c *pdata; struct resource *res; int ret; pdata = pdev->dev.platform_data; if (!pdata) { dev_err(&pdev->dev, "no platform data/n"); return -EINVAL; }        //给s3c24xx_i2c结构体申请空间 i2c = kzalloc(sizeof(struct s3c24xx_i2c), GFP_KERNEL); if (!i2c) { dev_err(&pdev->dev, "no memory for state/n"); return -ENOMEM; }        //填充s3c24xx_i2c结构体中各项，包括名称、所有者、算法、所属class等等 strlcpy(i2c->adap.name, "s3c2410-i2c", sizeof(i2c->adap.name)); i2c->adap.owner   = THIS_MODULE; i2c->adap.algo    = &s3c24xx_i2c_algorithm; //这个下面会重点介绍 i2c->adap.retries = 2; i2c->adap.class   = I2C_CLASS_HWMON | I2C_CLASS_SPD; i2c->tx_setup     = 50; spin_lock_init(&i2c->lock); init_waitqueue_head(&i2c->wait); /* find the clock and enable it */        // 找到i2c始终并且使能它 i2c->dev = &pdev->dev; i2c->clk = clk_get(&pdev->dev, "i2c"); if (IS_ERR(i2c->clk)) { dev_err(&pdev->dev, "cannot get clock/n"); ret = -ENOENT; goto err_noclk; } dev_dbg(&pdev->dev, "clock source %p/n", i2c->clk); clk_enable(i2c->clk); /* map the registers */        /*映射寄存器*/ res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if (res == NULL) { dev_err(&pdev->dev, "cannot find IO resource/n"); ret = -ENOENT; goto err_clk; } i2c->ioarea = request_mem_region(res->start, resource_size(res), pdev->name); if (i2c->ioarea == NULL) { dev_err(&pdev->dev, "cannot request IO/n"); ret = -ENXIO; goto err_clk; } i2c->regs = ioremap(res->start, resource_size(res)); if (i2c->regs == NULL) { dev_err(&pdev->dev, "cannot map IO/n"); ret = -ENXIO; goto err_ioarea; } dev_dbg(&pdev->dev, "registers %p (%p, %p)/n", i2c->regs, i2c->ioarea, res); /* setup info block for the i2c core */ i2c->adap.algo_data = i2c; i2c->adap.dev.parent = &pdev->dev; /* initialise the i2c controller */        /*s3c24xx_i2c结构体变量i2c的必要的信息都填充完了以后，开始进行初始化*/ ret = s3c24xx_i2c_init(i2c); if (ret != 0) goto err_iomap; /* find the IRQ for this unit (note, this relies on the init call to * ensure no current IRQs pending */        //接下来申请中断 i2c->irq = ret = platform_get_irq(pdev, 0); if (ret <= 0) { dev_err(&pdev->dev, "cannot find IRQ/n"); goto err_iomap; } ret = request_irq(i2c->irq, s3c24xx_i2c_irq, IRQF_DISABLED,   dev_name(&pdev->dev), i2c); if (ret != 0) { dev_err(&pdev->dev, "cannot claim IRQ %d/n", i2c->irq); goto err_iomap; }        ret = s3c24xx_i2c_register_cpufreq(i2c); if (ret < 0) { dev_err(&pdev->dev, "failed to register cpufreq notifier/n"); goto err_irq; } /* Note, previous versions of the driver used i2c_add_adapter() * to add the bus at any number. We now pass the bus number via * the platform data, so if unset it will now default to always * being bus 0. */ i2c->adap.nr = pdata->bus_num;        //看到了吧？下面调用了i2c-core中的i2c_add_adapter函数来添加一个i2c控制器          //i2c_add_numbered_adapter和i2c_add_adapter的区别在于前者用来添加一个在CPU内          //部集成的适配器，而后者用来添加一个CPU外部的适配器。显然这里应该用前者。 ret = i2c_add_numbered_adapter(&i2c->adap); if (ret < 0) { dev_err(&pdev->dev, "failed to add bus to i2c core/n"); goto err_cpufreq; } platform_set_drvdata(pdev, i2c); dev_info(&pdev->dev, "%s: S3C I2C adapter/n", dev_name(&i2c->adap.dev)); return 0; err_cpufreq: s3c24xx_i2c_deregister_cpufreq(i2c); err_irq: free_irq(i2c->irq, i2c); err_iomap: iounmap(i2c->regs); err_ioarea: release_resource(i2c->ioarea); kfree(i2c->ioarea); err_clk: clk_disable(i2c->clk); clk_put(i2c->clk); err_noclk: kfree(i2c); return ret; }

*remove函数

这是和probe相反的一个函数，在i2c_adap_s3c_exit时调用。主要功能是注销适配器，释放中断，释放内存区域，禁止始终等等。看到上边代码中的err_的各个部分了吧？ remove是它们的汇总。

*suspend函数和resume函数

把这两个放一起说吧，挂起和恢复函数。挂起时保存状态并置标志位，恢复时重新初始化i2c适配器并置标志位。

Algorithm

哎呀我去，终于到这了。憋得我难受啊。这里要重点介绍一下，不仅要知其然，还要知其所以然，这样我们以后自己写驱动的时候就有把握了。

static const struct i2c_algorithm s3c24xx_i2c_algorithm = {
    .master_xfer        = s3c24xx_i2c_xfer,
    .functionality      = s3c24xx_i2c_func,
};

static const struct i2c_algorithm s3c24xx_i2c_algorithm = { .master_xfer = s3c24xx_i2c_xfer, .functionality = s3c24xx_i2c_func, };

这里实现的就是这个s3c24xx_i2c_xfer。这个是控制器能不能动作的关键，缺了这个，控制器就是废铜烂铁。

static int s3c24xx_i2c_xfer(struct i2c_adapter *adap,
            struct i2c_msg *msgs, int num)
{
    struct s3c24xx_i2c *i2c = (struct s3c24xx_i2c *)adap->algo_data;
    int retry;
    int ret;

    for (retry = 0; retry < adap->retries; retry++) {

        ret = s3c24xx_i2c_doxfer(i2c, msgs, num);

        if (ret != -EAGAIN)
            return ret;

        dev_dbg(i2c->dev, "Retrying transmission (%d)/n", retry);

        udelay(100);
    }

    return -EREMOTEIO;
}

static int s3c24xx_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) { struct s3c24xx_i2c *i2c = (struct s3c24xx_i2c *)adap->algo_data; int retry; int ret; for (retry = 0; retry < adap->retries; retry++) { ret = s3c24xx_i2c_doxfer(i2c, msgs, num); if (ret != -EAGAIN) return ret; dev_dbg(i2c->dev, "Retrying transmission (%d)/n", retry); udelay(100); } return -EREMOTEIO; }

完成任务的函数是s3c24xx_i2c_doxfer()，源码清单如下，

static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
                  struct i2c_msg *msgs, int num)
{
    unsigned long timeout;
    int ret;

    if (i2c->suspended)
        return -EIO;

    ret = s3c24xx_i2c_set_master(i2c);
    if (ret != 0) {
        dev_err(i2c->dev, "cannot get bus (error %d)/n", ret);
        ret = -EAGAIN;
        goto out;
    }

    spin_lock_irq(&i2c->lock);

    i2c->msg     = msgs;
    i2c->msg_num = num;
    i2c->msg_ptr = 0;
    i2c->msg_idx = 0;
    i2c->state   = STATE_START;

    s3c24xx_i2c_enable_irq(i2c);
    s3c24xx_i2c_message_start(i2c, msgs);
    spin_unlock_irq(&i2c->lock);

    timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5);

    ret = i2c->msg_idx;

    /* having these next two as dev_err() makes life very
     * noisy when doing an i2cdetect */

    if (timeout == 0)
        dev_dbg(i2c->dev, "timeout/n");
    else if (ret != num)
        dev_dbg(i2c->dev, "incomplete xfer (%d)/n", ret);

    /* ensure the stop has been through the bus */

    msleep(1);

out:
    return ret;
}

static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,       struct i2c_msg *msgs, int num) { unsigned long timeout; int ret; if (i2c->suspended) return -EIO; ret = s3c24xx_i2c_set_master(i2c); if (ret != 0) { dev_err(i2c->dev, "cannot get bus (error %d)/n", ret); ret = -EAGAIN; goto out; } spin_lock_irq(&i2c->lock); i2c->msg     = msgs; i2c->msg_num = num; i2c->msg_ptr = 0; i2c->msg_idx = 0; i2c->state   = STATE_START; s3c24xx_i2c_enable_irq(i2c); s3c24xx_i2c_message_start(i2c, msgs); spin_unlock_irq(&i2c->lock); timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5); ret = i2c->msg_idx; /* having these next two as dev_err() makes life very * noisy when doing an i2cdetect */ if (timeout == 0) dev_dbg(i2c->dev, "timeout/n"); else if (ret != num) dev_dbg(i2c->dev, "incomplete xfer (%d)/n", ret); /* ensure the stop has been through the bus */ msleep(1); out: return ret; }

上面代码可以分成几个部分来看：

  * s3c24xx_i2c_set_master() 这个函数每隔1ms查看一次i2c总线状态，timeout是400ms，如果在这期间总线状态不忙，则返回零。否则返回-ETIMEDOUT

  * 将要发送的消息和其他信息付给i2c->msg和其他变量，并将状态设置为STATE_START

  * s3c24xx_i2c_enable_irq() 使能中断

  * s3c24xx_i2c_message_start() 重中之重啊。在看代码之前先来看看2440的datasheet上是怎么说的吧。

代码清单如下：

static void s3c24xx_i2c_message_start(struct s3c24xx_i2c *i2c,
                      struct i2c_msg *msg)
{
    unsigned int addr = (msg->addr & 0x7f) << 1;
    unsigned long stat;
    unsigned long iiccon;

    stat = 0;
    stat |=  S3C2410_IICSTAT_TXRXEN;

    if (msg->flags & I2C_M_RD) {//如果是read data, from slave to master     stat |= S3C2410_IICSTAT_MASTER_RX;
        addr |= 1;
    } else
        stat |= S3C2410_IICSTAT_MASTER_TX;

    if (msg->flags & I2C_M_REV_DIR_ADDR)
        addr ^= 1;

    /* todo - check for wether ack wanted or not */
    s3c24xx_i2c_enable_ack(i2c);

    iiccon = readl(i2c->regs + S3C2410_IICCON);
    writel(stat, i2c->regs + S3C2410_IICSTAT);

    dev_dbg(i2c->dev, "START: %08lx to IICSTAT, %02x to DS/n", stat, addr);
    writeb(addr, i2c->regs + S3C2410_IICDS);

    /* delay here to ensure the data byte has gotten onto the bus
     * before the transaction is started */

    ndelay(i2c->tx_setup);

    dev_dbg(i2c->dev, "iiccon, %08lx/n", iiccon);
    writel(iiccon, i2c->regs + S3C2410_IICCON);

    stat |= S3C2410_IICSTAT_START;
    writel(stat, i2c->regs + S3C2410_IICSTAT);
}

http://blog.csdn.net/ypoflyer/article/details/6382097