Android 电池管理系统-驱动部分

硬件平台：RK3128

Android版本：6.0

Kernel版本：3.10.92

    Android电池管理，基于linux Power Supply架构，Battery驱动程序需要通过sys文件系统向用户空间提供接口，Linux标准的Power Supply驱动程序所使用的文件系统路径问/sys/class/power_supply,其中的每个子目录表示一种能源供应设备的名称。

一、Power Supply初始化

先来看看power_supply结构体，定义在include/linux/power_supply.h中。

struct power_supply {
	const char *name; /*名称*/
	enum power_supply_type type;/*类型*/
	enum power_supply_property *properties;/*属性*/
	size_t num_properties;/*属性数目*/

	char **supplied_to;
	size_t num_supplicants;

	char **supplied_from;
	size_t num_supplies;
#ifdef CONFIG_OF
	struct device_node *of_node;
#endif

	int (*get_property)(struct power_supply *psy,
			    enum power_supply_property psp,
			    union power_supply_propval *val);
	int (*set_property)(struct power_supply *psy,
			    enum power_supply_property psp,
			    const union power_supply_propval *val);
	int (*property_is_writeable)(struct power_supply *psy,
				     enum power_supply_property psp);
	void (*external_power_changed)(struct power_supply *psy);
	void (*set_charged)(struct power_supply *psy);

	/* For APM emulation, think legacy userspace. */
	int use_for_apm;

	/* private */
	struct device *dev;
	struct work_struct changed_work;
	spinlock_t changed_lock;
	bool changed;
#ifdef CONFIG_THERMAL
	struct thermal_zone_device *tzd;
	struct thermal_cooling_device *tcd;
#endif

#ifdef CONFIG_LEDS_TRIGGERS
	struct led_trigger *charging_full_trig;
	char *charging_full_trig_name;
	struct led_trigger *charging_trig;
	char *charging_trig_name;
	struct led_trigger *full_trig;
	char *full_trig_name;
	struct led_trigger *online_trig;
	char *online_trig_name;
	struct led_trigger *charging_blink_full_solid_trig;
	char *charging_blink_full_solid_trig_name;
#endif
};

初始化：

drivers/power/power_supply_core.c

static int __init power_supply_class_init(void)
{
	power_supply_class = class_create(THIS_MODULE, "power_supply");

	if (IS_ERR(power_supply_class))
		return PTR_ERR(power_supply_class);

	power_supply_class->dev_uevent = power_supply_uevent;
	power_supply_init_attrs(&power_supply_dev_type);

	return 0;
}

可以看到创建了class power_supply，也就是/sys/class/power_supply，接着绑定了dev_uevent，dev_uevent是结构体class的一个函数指针，定义在include/linux/device.h中，看看源码中的描述：

 * @dev_uevent:	Called when a device is added, removed from this class, or a
 *		few other things that generate uevents to add the environment
 *		variables.

也就是说每添加一个设备到power_supply中，就会调用一次power_supply_uevent。

注册：

int power_supply_register(struct device *parent, struct power_supply *psy)
{
	struct device *dev;
	int rc;

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		return -ENOMEM;

	device_initialize(dev);

	dev->class = power_supply_class;
	dev->type = &power_supply_dev_type;
	dev->parent = parent;
	dev->release = power_supply_dev_release;
	dev_set_drvdata(dev, psy);
	psy->dev = dev;

	INIT_WORK(&psy->changed_work, power_supply_changed_work);

	rc = power_supply_check_supplies(psy);
	if (rc) {
		dev_info(dev, "Not all required supplies found, defer probe\n");
		goto check_supplies_failed;
	}

	rc = kobject_set_name(&dev->kobj, "%s", psy->name);
	if (rc)
		goto kobject_set_name_failed;

	rc = device_add(dev);
	if (rc)
		goto device_add_failed;

	spin_lock_init(&psy->changed_lock);
	rc = device_init_wakeup(dev, true);
	if (rc)
		goto wakeup_init_failed;

	rc = psy_register_thermal(psy);
	if (rc)
		goto register_thermal_failed;

	rc = psy_register_cooler(psy);
	if (rc)
		goto register_cooler_failed;

	rc = power_supply_create_triggers(psy);
	if (rc)
		goto create_triggers_failed;

	power_supply_changed(psy);

	goto success;

create_triggers_failed:
	psy_unregister_cooler(psy);
register_cooler_failed:
	psy_unregister_thermal(psy);
register_thermal_failed:
wakeup_init_failed:
	device_del(dev);
kobject_set_name_failed:
device_add_failed:
check_supplies_failed:
	put_device(dev);
success:
	return rc;
}

再看看drivers/power/power_supply_sysfs.c

/* Must be in the same order as POWER_SUPPLY_PROP_* */
static struct device_attribute power_supply_attrs[] = {
	/* Properties of type `int' */
	POWER_SUPPLY_ATTR(status),
	POWER_SUPPLY_ATTR(charge_type),
	POWER_SUPPLY_ATTR(health),
	POWER_SUPPLY_ATTR(present),
	POWER_SUPPLY_ATTR(online),
	POWER_SUPPLY_ATTR(authentic),
	POWER_SUPPLY_ATTR(technology),
	POWER_SUPPLY_ATTR(cycle_count),
	POWER_SUPPLY_ATTR(voltage_max),
	POWER_SUPPLY_ATTR(voltage_min),
	POWER_SUPPLY_ATTR(voltage_max_design),
	POWER_SUPPLY_ATTR(voltage_min_design),
        ...
        ...

这里是所有的电源设备属性，但并不需要全部创建，需要创建哪些由我们注册时指定，把需要创建的属性放在properties中即可，在power_supply_uevent中很容易可以看到：

	for (j = 0; j < psy->num_properties; j++) {
		struct device_attribute *attr;
		char *line;

		attr = &power_supply_attrs[psy->properties[j]];

		ret = power_supply_show_property(dev, attr, prop_buf);
		if (ret == -ENODEV || ret == -ENODATA) {
			/* When a battery is absent, we expect -ENODEV. Don't abort;
			   send the uevent with at least the the PRESENT=0 property */
			ret = 0;
			continue;
		}

psy即我们传入的power_supply。

二、Battery driver

Battery driver通过power_supply_register注册到Power Supply core中，来看看源码：

	data ->bat = rk30_battery_supply;
	ret = power_supply_register(&pdev->dev,&data ->bat);

rk30_battery_supply：

static enum power_supply_property rk30_adc_battery_props[] = {

	POWER_SUPPLY_PROP_STATUS,
	POWER_SUPPLY_PROP_HEALTH,
	POWER_SUPPLY_PROP_PRESENT,
	POWER_SUPPLY_PROP_VOLTAGE_NOW,
	POWER_SUPPLY_PROP_TECHNOLOGY,
	POWER_SUPPLY_PROP_CAPACITY,
	POWER_SUPPLY_PROP_VOLTAGE_MAX_DESIGN,
	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
};

static struct power_supply rk30_battery_supply = 
{
	.name = "battery",
	.type = POWER_SUPPLY_TYPE_BATTERY,

	.get_property   = rk30_adc_battery_get_property,

	.properties     = rk30_adc_battery_props,
	.num_properties = ARRAY_SIZE(rk30_adc_battery_props),
};

rk30_adc_battery_props即指定了需要创建的节点列表。到这里Battery驱动就创建完成了。

三、电量更新

Android电量更新是通过uevent通知上层，battery driver会不断计算当前电量，当电量发生变化后，会调用power_supply_changed(&bat ->bat);

void power_supply_changed(struct power_supply *psy)
{
	unsigned long flags;

	dev_dbg(psy->dev, "%s\n", __func__);

	spin_lock_irqsave(&psy->changed_lock, flags);
	psy->changed = true;
	pm_stay_awake(psy->dev);
	spin_unlock_irqrestore(&psy->changed_lock, flags);
	schedule_work(&psy->changed_work);
}

changed_work：

static void power_supply_changed_work(struct work_struct *work)
{
	unsigned long flags;
	struct power_supply *psy = container_of(work, struct power_supply,
						changed_work);

	dev_dbg(psy->dev, "%s\n", __func__);

	spin_lock_irqsave(&psy->changed_lock, flags);
	if (psy->changed) {
		psy->changed = false;
		spin_unlock_irqrestore(&psy->changed_lock, flags);

		class_for_each_device(power_supply_class, NULL, psy,
				      __power_supply_changed_work);

		power_supply_update_leds(psy);

		kobject_uevent(&psy->dev->kobj, KOBJ_CHANGE);
		spin_lock_irqsave(&psy->changed_lock, flags);
	}
	if (!psy->changed)
		pm_relax(psy->dev);
	spin_unlock_irqrestore(&psy->changed_lock, flags);
}

可以看到changed_work中会调用kobject_uevent，其后流程如下：

kobject_uevent ->

kobject_uevent_env->

netlink_broadcast_filtered

通过netlink机制发送给framework用以更新电量，关于framework的部分会在下篇介绍。