linux启动过程分析（十一）---davinci_i2c_init_driver

参考博客：https://blog.youkuaiyun.com/li_wen01/article/details/51658881
I2c-davinci.c (drivers\i2c\busses):subsys_initcall(davinci_i2c_init_driver);
platform device已经注册完了，下面是platform driver的初始化。

/* I2C may be needed to bring up other drivers */
static int __init davinci_i2c_init_driver(void)
{
	return platform_driver_register(&davinci_i2c_driver);
}

davinci_i2c_driver被定义为：

static struct platform_driver davinci_i2c_driver = {
	.probe		= davinci_i2c_probe,
	.remove		= davinci_i2c_remove,
	.driver		= {
		.name	= "i2c_davinci",
		.owner	= THIS_MODULE,
		.pm	= davinci_i2c_pm_ops,
	},
};

展开前面的platform_driver_register(&davinci_i2c_driver)；

/**
 * platform_driver_register - register a driver for platform-level devices
 * @drv: platform driver structure
 */
int platform_driver_register(struct platform_driver *drv)
{
	drv->driver.bus = &platform_bus_type;
	if (drv->probe)
		drv->driver.probe = platform_drv_probe;
	if (drv->remove)
		drv->driver.remove = platform_drv_remove;
	if (drv->shutdown)
		drv->driver.shutdown = platform_drv_shutdown;

	return driver_register(&drv->driver);
}

最后再调用driver_register(davinci_i2c_driver.driver);
这个driver的结构如下：

.driver		= {
		.name	= "i2c_davinci",
		.owner	= THIS_MODULE,
		.pm	= davinci_i2c_pm_ops,
	},

/**
 * driver_register - register driver with bus
 * @drv: driver to register
 *
 * We pass off most of the work to the bus_add_driver() call,
 * since most of the things we have to do deal with the bus
 * structures.
 */
int driver_register(struct device_driver *drv)
{
	int ret;
	struct device_driver *other;

	BUG_ON(!drv->bus->p);
	/*看总线上是否已经挂载了该驱动*/
	if ((drv->bus->probe && drv->probe) ||
	    (drv->bus->remove && drv->remove) ||
	    (drv->bus->shutdown && drv->shutdown))
		printk(KERN_WARNING "Driver '%s' needs updating - please use "
			"bus_type methods\n", drv->name);
	/*检查该驱动是否已经注册*/
	other = driver_find(drv->name, drv->bus);
	if (other) {
		/*将驱动移除*/
		put_driver(other);
		printk(KERN_ERR "Error: Driver '%s' is already registered, "
			"aborting...\n", drv->name);
		return -EBUSY;
	}
	
	ret = bus_add_driver(drv);
	if (ret)
		return ret;
	ret = driver_add_groups(drv, drv->groups);
	if (ret)
		bus_remove_driver(drv);
	return ret;
}

接着分析bus_add_driver()函数：

/**
 * bus_add_driver - Add a driver to the bus.
 * @drv: driver.
 */
int bus_add_driver(struct device_driver *drv)
{
	struct bus_type *bus;
	struct driver_private *priv;
	int error = 0;

	bus = bus_get(drv->bus);
	if (!bus)
		return -EINVAL;

	pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv) {
		error = -ENOMEM;
		goto out_put_bus;
	}
	klist_init(&priv->klist_devices, NULL, NULL);
	priv->driver = drv;
	drv->p = priv;
	priv->kobj.kset = bus->p->drivers_kset;
	error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
				     "%s", drv->name);
	if (error)
		goto out_unregister;

	if (drv->bus->p->drivers_autoprobe) {
		/*进行platform device与platform driver的配对*/
		error = driver_attach(drv);
		if (error)
			goto out_unregister;
	}
	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
	module_add_driver(drv->owner, drv);

	error = driver_create_file(drv, &driver_attr_uevent);
	if (error) {
		printk(KERN_ERR "%s: uevent attr (%s) failed\n",
			__func__, drv->name);
	}
	error = driver_add_attrs(bus, drv);
	if (error) {
		/* How the hell do we get out of this pickle? Give up */
		printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
			__func__, drv->name);
	}

	if (!drv->suppress_bind_attrs) {
		/*进行platform device与platform driver的绑定*/
		error = add_bind_files(drv);
		if (error) {
			/* Ditto */
			printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
				__func__, drv->name);
		}
	}

	kobject_uevent(&priv->kobj, KOBJ_ADD);
	return 0;

out_unregister:
	kobject_put(&priv->kobj);
	kfree(drv->p);
	drv->p = NULL;
out_put_bus:
	bus_put(bus);
	return error;
}

进行platform device与platform driver 的配对是由driver_attach(drv)来完成的。
进行platform device 与platform driver 的绑定是由add_bind_files(drv)来完成的。下面来看一下这个绑定函数：

/*
 * Thanks to drivers making their tables __devinit, we can't allow manual
 * bind and unbind from userspace unless CONFIG_HOTPLUG is enabled.
 */
static int __must_check add_bind_files(struct device_driver *drv)
{
	int ret;

	ret = driver_create_file(drv, &driver_attr_unbind);
	if (ret == 0) {
		ret = driver_create_file(drv, &driver_attr_bind);
		if (ret)
			driver_remove_file(drv, &driver_attr_unbind);
	}
	return ret;
}

其中，driver_create_file(drv, &driver_attr_bind)会调用driver_bind函数，具体调用如下：

 在include\linux\Device.h中可以找到如下声明：
#define DRIVER_ATTR(_name, _mode, _show, _store)	\
struct driver_attribute driver_attr_##_name =		\
	__ATTR(_name, _mode, _show, _store)
 在drivers\base\bus.c中可以找到如下声明：
static DRIVER_ATTR(bind, S_IWUSR, NULL, driver_bind);

调用driver_bind函数之后：

/*
 * 自动匹配设备和驱动
 */
static ssize_t driver_bind(struct device_driver *drv,
			   const char *buf, size_t count)
{
	struct bus_type *bus = bus_get(drv->bus);
	struct device *dev;
	int err = -ENODEV;

	dev = bus_find_device_by_name(bus, NULL, buf);
	if (dev && dev->driver == NULL && driver_match_device(drv, dev)) {
		if (dev->parent)	/* Needed for USB */
			device_lock(dev->parent);
		device_lock(dev);
		err = driver_probe_device(drv, dev);
		device_unlock(dev);
		if (dev->parent)
			device_unlock(dev->parent);

		if (err > 0) {
			/* success */
			err = count;
		} else if (err == 0) {
			/* driver didn't accept device */
			err = -ENODEV;
		}
	}
	put_device(dev);
	bus_put(bus);
	return err;
}

再来分析probe函数：driver_probe_device(drv, dev)
->
ret = really_probe(dev, drv);
->
ret = drv->probe(dev);
这里调用的是davinci_i2c_probe函数：

static int davinci_i2c_probe(struct platform_device *pdev)
{
	struct davinci_i2c_dev *dev;
	struct i2c_adapter *adap;
	struct resource *mem, *irq, *ioarea;
	int r;

	/* NOTE: driver uses the static register mapping */
	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	if (!mem) {
		dev_err(&pdev->dev, "no mem resource?\n");
		return -ENODEV;
	}

	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
	if (!irq) {
		dev_err(&pdev->dev, "no irq resource?\n");
		return -ENODEV;
	}

	ioarea = request_mem_region(mem->start, resource_size(mem),
				    pdev->name);
	if (!ioarea) {
		dev_err(&pdev->dev, "I2C region already claimed\n");
		return -EBUSY;
	}

	dev = kzalloc(sizeof(struct davinci_i2c_dev), GFP_KERNEL);
	if (!dev) {
		r = -ENOMEM;
		goto err_release_region;
	}

	init_completion(&dev->cmd_complete);
#ifdef CONFIG_CPU_FREQ
	init_completion(&dev->xfr_complete);
#endif
	dev->dev = get_device(&pdev->dev);
	dev->irq = irq->start;
	platform_set_drvdata(pdev, dev);

	dev->clk = clk_get(&pdev->dev, NULL);
	if (IS_ERR(dev->clk)) {
		r = -ENODEV;
		goto err_free_mem;
	}
	clk_enable(dev->clk);

	dev->base = ioremap(mem->start, resource_size(mem));
	if (!dev->base) {
		r = -EBUSY;
		goto err_mem_ioremap;
	}
	/*复位I2C总线，计算预分频，时钟，寄存器设置，使能中断等*/
	i2c_davinci_init(dev);

	r = request_irq(dev->irq, i2c_davinci_isr, 0, pdev->name, dev);//申请中断，内核中i2c的读写通过中断实现
	if (r) {
		dev_err(&pdev->dev, "failure requesting irq %i\n", dev->irq);
		goto err_unuse_clocks;
	}

	r = i2c_davinci_cpufreq_register(dev);
	if (r) {
		dev_err(&pdev->dev, "failed to register cpufreq\n");
		goto err_free_irq;
	}

	adap = &dev->adapter;
	i2c_set_adapdata(adap, dev);
	adap->owner = THIS_MODULE;
	adap->class = I2C_CLASS_HWMON;
	strlcpy(adap->name, "DaVinci I2C adapter", sizeof(adap->name));
	adap->algo = &i2c_davinci_algo;//初始化algo算法
	adap->dev.parent = &pdev->dev;
	adap->timeout = DAVINCI_I2C_TIMEOUT;

	adap->nr = pdev->id;
	r = i2c_add_numbered_adapter(adap);//向系统注册一个i2c adapter
	if (r) {
		dev_err(&pdev->dev, "failure adding adapter\n");
		goto err_free_irq;
	}

	return 0;

err_free_irq:
	free_irq(dev->irq, dev);
err_unuse_clocks:
	iounmap(dev->base);
err_mem_ioremap:
	clk_disable(dev->clk);
	clk_put(dev->clk);
	dev->clk = NULL;
err_free_mem:
	platform_set_drvdata(pdev, NULL);
	put_device(&pdev->dev);
	kfree(dev);
err_release_region:
	release_mem_region(mem->start, resource_size(mem));

	return r;
}