1、thermal简介

? ? ?thermal模块主要负责温度控制，温度低时想办法升温，温度高时想办法降温，甚至复位系统。Linux kernel有个通用的思想就是抽象分层，比如把该子系统所有资源和信息综合在一起的一层叫core层，不同的设备的操作叫device层，对设备的操作的屏蔽层叫driver层或者governor。同样thermal子系统也是采用了该思想：核心为 thermal_core，可以获取温度的设备抽象为 thermal_zone_device, 如Temp Sensor、NTC(板上的热敏电阻)等。控制温度的设备抽象为 thermal_cooling_device, 如风扇、CPU、DDR、GPU等。温控策略抽象为 thermal_governor，比如 step_wise、bang_bang 等。

? ? ? ?thermal_cooling_device 对应系统实施冷却措施的驱动，是温控的执行者。cooling device 维护一个 cooling 等级，即 state，一般 state 越高即系统的冷却需求越高。cooling device 根据不同等级的冷却需求进行冷却行为。cooling device 只根据 state 进行冷却操作，是实施者，而 state 的计算由 thermal governor 完成。结构 struct cpufreq_cooling_device 和 struct devfreq_cooling_device 作为对 thermal_cooling_device 的扩展，分别主要在 cpufreq_cooling.c 和 devfreq_cooling.c?中使用。

2、thermal_core分析

? ? ? ?thermal_core作为thermal的核心部分，负责把governor\cool device\zone_device关联在一起，因此thermal_core就需要提供注册接口和作为记录的全局变量来记录注册的信息：

2.1 zone_device注册相关接口

2.1.1 关键结构体

/**
 * struct thermal_zone_device - structure for a thermal zone
 * @id:		unique id number for each thermal zone
 * @type:	the thermal zone device type
 * @device:	&struct device for this thermal zone
 * @trip_temp_attrs:	attributes for trip points for sysfs: trip temperature
 * @trip_type_attrs:	attributes for trip points for sysfs: trip type
 * @trip_hyst_attrs:	attributes for trip points for sysfs: trip hysteresis
 * @mode:		current mode of this thermal zone
 * @devdata:	private pointer for device private data
 * @trips:	number of trip points the thermal zone supports
 * @trips_disabled;	bitmap for disabled trips
 * @passive_delay_jiffies: number of jiffies to wait between polls when
 *			performing passive cooling.
 * @polling_delay_jiffies: number of jiffies to wait between polls when
 *			checking whether trip points have been crossed (0 for
 *			interrupt driven systems)
 * @temperature:	current temperature.  This is only for core code,
 *			drivers should use thermal_zone_get_temp() to get the
 *			current temperature
 * @last_temperature:	previous temperature read
 * @emul_temperature:	emulated temperature when using CONFIG_THERMAL_EMULATION
 * @passive:		1 if you've crossed a passive trip point, 0 otherwise.
 * @prev_low_trip:	the low current temperature if you've crossed a passive
			trip point.
 * @prev_high_trip:	the above current temperature if you've crossed a
			passive trip point.
 * @need_update:	if equals 1, thermal_zone_device_update needs to be invoked.
 * @ops:	operations this &thermal_zone_device supports
 * @tzp:	thermal zone parameters
 * @governor:	pointer to the governor for this thermal zone
 * @governor_data:	private pointer for governor data
 * @thermal_instances:	list of &struct thermal_instance of this thermal zone
 * @ida:	&struct ida to generate unique id for this zone's cooling
 *		devices
 * @lock:	lock to protect thermal_instances list
 * @node:	node in thermal_tz_list (in thermal_core.c)
 * @poll_queue:	delayed work for polling
 * @notify_event: Last notification event
 */
struct thermal_zone_device {
	int id;
	char type[THERMAL_NAME_LENGTH];
	struct device device;
	struct attribute_group trips_attribute_group;
	struct thermal_attr *trip_temp_attrs;
	struct thermal_attr *trip_type_attrs;
	struct thermal_attr *trip_hyst_attrs;
	enum thermal_device_mode mode;
	void *devdata;
	int trips;
	unsigned long trips_disabled;	/* bitmap for disabled trips */
	unsigned long passive_delay_jiffies;
	unsigned long polling_delay_jiffies;
	int temperature;
	int last_temperature;
	int emul_temperature;
	int passive;
	int prev_low_trip;
	int prev_high_trip;
	atomic_t need_update;
	struct thermal_zone_device_ops *ops;
	struct thermal_zone_params *tzp;
	struct thermal_governor *governor;
	void *governor_data;
	struct list_head thermal_instances;
	struct ida ida;
	struct mutex lock;
	struct list_head node;
	struct delayed_work poll_queue;
	enum thermal_notify_event notify_event;
};

2.1.2 接口

1、thermal_zone_device_register：zone_device注册接口，需要注册时需要调用该接口来注册。该接口中主要实现以下功能：

1）给zone_device赋值critical接口，再温度过高时，critical接口负责重启系统

2）关联上匹配的governor

3）把该zone_device添加到thermal_tz_list中

4）给该zone_device绑定上相关的cooling_device

5）创建zone_device的温度监控任务

2、thermal_zone_device_unregister：zone_device去注册接口，需要去注册时需要调用该接口来注册。该接口实现的主要功能如下：

1）device从thermal_tz_list中删除

2）对应任务删除

3）对应的governor置空

2.2 Cooling_device注册相关接口

2.2.1关键结构体

struct thermal_cooling_device_ops {
	int (*get_max_state) (struct thermal_cooling_device *, unsigned long *);
	int (*get_cur_state) (struct thermal_cooling_device *, unsigned long *);
	int (*set_cur_state) (struct thermal_cooling_device *, unsigned long);
	int (*get_requested_power)(struct thermal_cooling_device *, u32 *);
	int (*state2power)(struct thermal_cooling_device *, unsigned long, u32 *);
	int (*power2state)(struct thermal_cooling_device *, u32, unsigned long *);
};

struct thermal_cooling_device {
	int id;
	char *type;
	struct device device;
	struct device_node *np;
	void *devdata;
	void *stats;
	const struct thermal_cooling_device_ops *ops;
	bool updated; /* true if the cooling device does not need update */
	struct mutex lock; /* protect thermal_instances list */
	struct list_head thermal_instances;
	struct list_head node;
};

2.2.2 接口

1、thermal_cooling_device_register：cooling_device注册接口，cooling_device_ops有3个非常重要的接口，分别是get_max_state、get_cur_state、set_cur_state，分别用于获取最大状态、获取当前状态、设置当前状态，关于state，前边第一节我们介绍了，就不再赘述。该接口实现的主要功能有：

1）添加该device到thermal_cdev_list中

2）Cooling_device与zone_device绑定

3）调用thermal_zone_device_update来更新温度及做对应处理

2、thermal_cooling_device_unregister：与thermal_cooling_device_register互为逆操作。

实现的主要功能有：

1）从hermal_cdev_list中删除该device

2）与zone device解绑定

2.3 Governors注册相关接口

? ? ? ?Thermal的governor都是通过THERMAL_GOVERNOR_DECLARE定义到了__thermal_table_entry_这段空间内，然后在thermal core初始化时通过调用thermal_register_governors来注册到thermal_governor_list链表中。

thermal_init->thermal_register_governors->?thermal_set_governor(和zone device关联上)