android linux内核分析（-）- led(上)

linux版本：version linux 3.x

android版本：android 4.4.2

分析实例：leds-s3c24xx.c

分析目录：dirvers/leds/

1.makefile

# LED Core
obj-$(CONFIG_NEW_LEDS)			+= led-core.o
obj-$(CONFIG_LEDS_CLASS)		+= led-class.o
obj-$(CONFIG_LEDS_TRIGGERS)		+= led-triggers.o

# LED Platform Drivers
obj-$(CONFIG_LEDS_88PM860X)		+= leds-88pm860x.o
obj-$(CONFIG_LEDS_ATMEL_PWM)		+= leds-atmel-pwm.o
obj-$(CONFIG_LEDS_BD2802)		+= leds-bd2802.o
obj-$(CONFIG_LEDS_LOCOMO)		+= leds-locomo.o
obj-$(CONFIG_LEDS_LM3530)		+= leds-lm3530.o
obj-$(CONFIG_LEDS_LM3533)		+= leds-lm3533.o
obj-$(CONFIG_LEDS_LM3642)		+= leds-lm3642.o
obj-$(CONFIG_LEDS_MIKROTIK_RB532)	+= leds-rb532.o
obj-$(CONFIG_LEDS_S3C24XX)		+= leds-s3c24xx.o

这个只是其中的一部分，无非是根据是否配置宏来决定是否编译对应的c文件。

2.Kconfig

config LEDS_S3C24XX
	tristate "LED Support for Samsung S3C24XX GPIO LEDs"
	depends on LEDS_CLASS
	depends on ARCH_S3C24XX
	help
	  This option enables support for LEDs connected to GPIO lines
	  on Samsung S3C24XX series CPUs, such as the S3C2410 and S3C2440.

这个其实是配置CONFIG_LEDS_S3C24XX
但是一般标准的配置其实是在\android\common\common\arch\arm\configs/下有很多的def_config,找到对应的你平台上的config即可，看其中是否配置了这些选项，找不到的话有两种办法看你修改的这个文件是否编译了

(1)主动在你的这个文件中添加错误，编译一次看是否报错

(2)在andoid中编译的out/target/product/xxx/obj/KERNEL_OBJ/中的.config中可以找到是否已经配置了，前提是已经编译了。

还有一个方式是直接让这个makefile中修改，直接了当，即

obj-y +＝leds-s3c24xx.o
这个有点暴力，不推荐

3.C文件

module_platform_driver(s3c24xx_led_driver);

MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>");
MODULE_DESCRIPTION("S3C24XX LED driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:s3c24xx_led");

下面的宏就不介绍了，看

module_platform_driver(s3c24xx_led_driver);

定义是这样的，Platform_device.h     \include\linux 

/* module_platform_driver() - Helper macro for drivers that don't do
 * anything special in module init/exit.  This eliminates a lot of
 * boilerplate.  Each module may only use this macro once, and
 * calling it replaces module_init() and module_exit()
 */
#define module_platform_driver(__platform_driver) \
	module_driver(__platform_driver, platform_driver_register, \

<pre name="code" class="cpp">#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \
	return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \
	__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);

唉，不过是换汤不换药，依然是__init,__exit,platform_driver_register(struct platform_driver *); platform_driver_unregister(struct platform_driver *);

好看platform_driver_register(struct platform_driver *);  在Platform.c (common\drivers\base)

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);
}

@1:此时的drv为传入参数s3c24xx_led_driver，而s3c24xx_led_driver的定义是

static struct platform_driver s3c24xx_led_driver = {
	.probe		= s3c24xx_led_probe,
	.remove		= s3c24xx_led_remove,
	.driver		= {
		.name		= "s3c24xx_led",
		.owner		= THIS_MODULE,
	},
};

而platform_driver 的定义是

struct platform_driver {
	int (*probe)(struct platform_device *);
	int (*remove)(struct platform_device *);
	void (*shutdown)(struct platform_device *);
	int (*suspend)(struct platform_device *, pm_message_t state);
	int (*resume)(struct platform_device *);
	struct device_driver driver;
	const struct platform_device_id *id_table;
};

需要注意的是struct device_driver driver; deice_driver定义是

struct device_driver {
	const char		*name;
	struct bus_type		*bus;

	struct module		*owner;
	const char		*mod_name;	/* used for built-in modules */

	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */

	const struct of_device_id	*of_match_table;
	const struct acpi_device_id	*acpi_match_table;

	int (*probe) (struct device *dev);
	int (*remove) (struct device *dev);
	void (*shutdown) (struct device *dev);
	int (*suspend) (struct device *dev, pm_message_t state);
	int (*resume) (struct device *dev);
	const struct attribute_group **groups;

	const struct dev_pm_ops *pm;

	struct driver_private *p;
};

@2：对s3c24xx_led_driver中的driver字段中的bus初始化为platform_bus_type

即s3c24xx_led_driver.driver->bus->&platform_bus_type
    s3c24xx_led_driver.driver->probe->platform_drv_probe

    s3c24xx_led_driver->driver.remove ->platform_drv_remove

    s3c24xx_led_driver->driver.shutdown ->platform_drv_shutdown

@3:

   driver_register(&drv->driver);   即注册driver_register(s3c24xx_led_driver.driver)

int driver_register(struct device_driver *drv)
{
	int ret;
	struct device_driver *other;

	BUG_ON(!drv->bus->p);

	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);

	other = driver_find(drv->name, drv->bus);
	if (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;
	}
	kobject_uevent(&drv->p->kobj, KOBJ_ADD);

	return ret;
}

@4:先检测一大堆函数指针，看是不是为NULL，为NULL的话会打出log；

@5：driver_find，是在寻找在bus上是否有相同的名字的设备驱动，假如有的话，那返回值不为空，说明之前已经注册过了，不能重复注册，为空，继续往下执行。

@6：真正重要的是bus_add_driver

/**
 * 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;

	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
	if (drv->bus->p->drivers_autoprobe) {
		error = driver_attach(drv);
		if (error)
			goto out_unregister;
	}
	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) {
		error = add_bind_files(drv);
		if (error) {
			/* Ditto */
			printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
				__func__, drv->name);
		}
	}

	return 0;

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

@1：传入的参数是drv 实际上s3c24xx_led_driver.driver，通过前面的赋值操作

@2：klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers); 将node_bus的链表上加入驱动drivers

@3：判断drv->bus->p->drivers_autoprobe是否为真，这个值在bus_register中已经设置了。

@4: driver_attach(drv);  ->bus_for_each_dev(drv->bus, NULL, drv, __driver_attach); 

int bus_for_each_dev(struct bus_type *bus, struct device *start,
		     void *data, int (*fn)(struct device *, void *))
{
	struct klist_iter i;
	struct device *dev;
	int error = 0;

	if (!bus || !bus->p)
		return -EINVAL;

	klist_iter_init_node(&bus->p->klist_devices, &i,
			     (start ? &start->p->knode_bus : NULL));
	while ((dev = next_device(&i)) && !error)
		error = fn(dev, data);
	klist_iter_exit(&i);
	return error;
}

@1:Klist 的迭代器，start 为NULL，调用fn，即__driver_attach(dev,data);

static int __driver_attach(struct device *dev, void *data)
{
	struct device_driver *drv = data;

	/*
	 * Lock device and try to bind to it. We drop the error
	 * here and always return 0, because we need to keep trying
	 * to bind to devices and some drivers will return an error
	 * simply if it didn't support the device.
	 *
	 * driver_probe_device() will spit a warning if there
	 * is an error.
	 */

	if (!driver_match_device(drv, dev))
		return 0;

	if (dev->parent)	/* Needed for USB */
		device_lock(dev->parent);
	device_lock(dev);
	if (!dev->driver)
		driver_probe_device(drv, dev);
	device_unlock(dev);
	if (dev->parent)
		device_unlock(dev->parent);

	return 0;
}

@1:driver_match_device调用的实际是 platform_match

@2：driver_probe_device(drv, dev); 

int driver_probe_device(struct device_driver *drv, struct device *dev)
{
	int ret = 0;

	if (!device_is_registered(dev))
		return -ENODEV;

	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
		 drv->bus->name, __func__, dev_name(dev), drv->name);

	pm_runtime_barrier(dev);
	ret = really_probe(dev, drv);
	pm_request_idle(dev);

	return ret;
}

@1：really_probe(dev, drv); 正真调用probe的地方。

static int really_probe(struct device *dev, struct device_driver *drv)
{
	int ret = 0;

	atomic_inc(&probe_count);
	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
		 drv->bus->name, __func__, drv->name, dev_name(dev));
	WARN_ON(!list_empty(&dev->devres_head));

	dev->driver = drv;

	/* If using pinctrl, bind pins now before probing */
	//ret = pinctrl_bind_pins(dev);
	//if (ret)
		//goto probe_failed;

	if (driver_sysfs_add(dev)) {
		printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
			__func__, dev_name(dev));
		goto probe_failed;
	}

	if (dev->bus->probe) {
		ret = dev->bus->probe(dev);
		if (ret)
			goto probe_failed;
	} else if (drv->probe) {
		ret = drv->probe(dev);
		if (ret)
			goto probe_failed;
	}

	driver_bound(dev);
	ret = 1;
	pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
		 drv->bus->name, __func__, dev_name(dev), drv->name);
	goto done;

probe_failed:
	devres_release_all(dev);
	driver_sysfs_remove(dev);
	dev->driver = NULL;
	dev_set_drvdata(dev, NULL);

	if (ret == -EPROBE_DEFER) {
		/* Driver requested deferred probing */
		dev_info(dev, "Driver %s requests probe deferral\n", drv->name);
		driver_deferred_probe_add(dev);
	} else if (ret != -ENODEV && ret != -ENXIO) {
		/* driver matched but the probe failed */
		printk(KERN_WARNING
		       "%s: probe of %s failed with error %d\n",
		       drv->name, dev_name(dev), ret);
	} else {
		pr_debug("%s: probe of %s rejects match %d\n",
		       drv->name, dev_name(dev), ret);
	}
	/*
	 * Ignore errors returned by ->probe so that the next driver can try
	 * its luck.
	 */
	ret = 0;
done:
	atomic_dec(&probe_count);
	wake_up(&probe_waitqueue);
	return ret;
}

@1：

else if (drv->probe) {
		ret = drv->probe(dev);
		if (ret)
			goto probe_failed;
	}

drv = s3c24xx_led_driver.driver 那么即s3c24xx_led_driver.driver ->probe,那么调用的是s3c24xx_led_probe，

@2“：dev.platform_data 这个从哪里来的，Common-smdk.c (common\arch\arm\mach-s3c24xx) 这个文件中定义的是smdk_machine_init

static struct platform_device __initdata *smdk_devs[] = {
	&s3c_device_nand,
	&smdk_led4,
	&smdk_led5,
	&smdk_led6,
	&smdk_led7,
};

static struct platform_device smdk_led4 = {
	.name		= "s3c24xx_led",
	.id		= 0,
	.dev		= {
		.platform_data = &smdk_pdata_led4,
	},
};

static struct s3c24xx_led_platdata smdk_pdata_led4 = {
	.gpio		= S3C2410_GPF(4),
	.flags		= S3C24XX_LEDF_ACTLOW | S3C24XX_LEDF_TRISTATE,
	.name		= "led4",
	.def_trigger	= "timer",
};

@3：led_classdev_register(&dev->dev, &led->cdev);

int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
{
	led_cdev->dev = device_create(leds_class, parent, 0, led_cdev,
				      "%s", led_cdev->name);
	if (IS_ERR(led_cdev->dev))
		return PTR_ERR(led_cdev->dev);

#ifdef CONFIG_LEDS_TRIGGERS
	init_rwsem(&led_cdev->trigger_lock);
#endif
	/* add to the list of leds */
	down_write(&leds_list_lock);
	list_add_tail(&led_cdev->node, &leds_list);
	up_write(&leds_list_lock);

	if (!led_cdev->max_brightness)
		led_cdev->max_brightness = LED_FULL;

	led_update_brightness(led_cdev);

	INIT_WORK(&led_cdev->set_brightness_work, set_brightness_delayed);

	init_timer(&led_cdev->blink_timer);
	led_cdev->blink_timer.function = led_timer_function;
	led_cdev->blink_timer.data = (unsigned long)led_cdev;

#ifdef CONFIG_LEDS_TRIGGERS
	led_trigger_set_default(led_cdev);
#endif

	dev_dbg(parent, "Registered led device: %s\n",
			led_cdev->name);

	return 0;
}

@1：list_add_tail(&led_cdev->node, &leds_list); 将led_s3c24xx的led_cdev中添加到led_list 的list中。