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thermal子系統(tǒng)概述
thermal子系統(tǒng)是內(nèi)核提供的溫控管理框架，一套軟件溫度解決方案，配合ic內(nèi)部溫度傳感器，對ic溫度進行管控，保證系統(tǒng)穩(wěn)定性。
thermal系統(tǒng)多用于對ic內(nèi)部的重點發(fā)熱模塊的功能管控，如cpu、gpu。
thermal sensor驅(qū)動負責(zé)讀取硬件溫度sensor的溫度，并傳給thermal 子系統(tǒng)，thermal子系統(tǒng)將根據(jù)調(diào)控對象的溫度，決定是否觸發(fā)對應(yīng)的冷卻措施，如限制CPU最大工作頻率，以及CPU打開的核數(shù)等，從而實現(xiàn)對系統(tǒng)的冷卻。
thermal zone
Thermal zone代表一個溫控管理區(qū)間，可以將其看做一個虛擬意義上的溫度Sensor， 需要有對應(yīng)的物理Sensor與其關(guān)聯(lián)再能發(fā)揮作用。
一個Thermal Zone最多可以關(guān)聯(lián)一個Sensor，但該Sensor可以是多個硬件Sensor的混合。
Trip Point
即觸發(fā)點，由Thermal Zone維護。每個thermal zone可以維護多個trip point。Trip Point包含以下信息：
temp：觸發(fā)溫度，當溫度到達觸發(fā)溫度則該trip point被觸發(fā)。
type：trip point類型，沿襲PC散熱方式，分為四種類型—passive、active、hot、critical。
cooling device綁定信息：
記錄在thermal_instance結(jié)構(gòu)體中，描述trip point與cooling device的綁定關(guān)系，即當trip point觸發(fā)后由那個cooling device去實施冷卻措施。每個trip point必須與一個cooling device綁定，才有實際意義。
cooling device
實際對系統(tǒng)實施冷卻措施的驅(qū)動，溫控的執(zhí)行者。cooling device 維護一個cooling等級，即state，一般state越高即系統(tǒng)的冷卻需求越高。cooling device根據(jù)不同等級的冷卻需求進行冷卻行為。
cooling device只根據(jù)state進行冷卻操作，是實施者，而state的計算由thermal governor完成。
thermal軟件框架
要實現(xiàn)一個溫度控制的需求，試想一下我們是不是最少要有獲取溫度的設(shè)備和控制溫度的設(shè)備這兩個最基本的東西？當然附帶的也會產(chǎn)生一些使用溫度控制設(shè)備的策略。
那上面這些東西在 Linux Thermal 框架中怎么體現(xiàn)呢？通過閱讀源碼我們發(fā)現(xiàn)代碼中對上面的東西進行了一些抽象。
獲取溫度的設(shè)備：在 Thermal 框架中被抽象為 Thermal Zone Device;
控制溫度的設(shè)備：在 Thermal 框架中被抽象為 Thermal Cooling Device;
控制溫度策略：在 Thermal 框架中被抽象為 Thermal Governor;
thermal zone
dts里的配置如下：
thermal-zones{
??????????? cpu_thermal_zone{
??????????????? polling-delay-passive = <1000>; //超過閥值輪詢時間
??????????????? polling-delay = <2000>; //未超閥值輪詢時間
??????????????? thermal-sensors = <&ths_combine0 0>;
??????????????? trips{
??????????????????? cpu_trip0:t0{
??????????????????????? temperature = <70>;
??????????????????????? type = "passive";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????????? cpu_trip1:t1{
??????????????????????? temperature = <90>;
??????????????????????? type = "passive";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????????? cpu_trip2:t2{
??????????????????????? temperature = <100>;
??????????????????????? type = "passive";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????????? cpu_trip3:t3{
??????????????????????? temperature = <105>;
??????????????????????? type = "passive";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????????? cpu_trip4:t4{
??????????????????????? temperature = <110>;
??????????????????????? type = "passive";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????????? crt_trip0:t5{
??????????????????????? temperature = <115>;
??????????????????????? type = "critical";
??????????????????????? hysteresis = <0>;
??????????????????? };
??????????????? };
??????????????? cooling-maps{
??????????????????? bind0{
??????????????????????? contribution = <0>;
??????????????????????? trip = <&cpu_trip0>;
??????????????????????? cooling-device = <&cpu_budget_cooling 1 1>;
??????????????????? };
??????????????????? bind1{
??????????????????????? contribution = <0>;
??????????????????????? trip = <&cpu_trip1>;
??????????????????????? cooling-device = <&cpu_budget_cooling 2 2>;
??????????????????? };
??????????????????? bind2{
??????????????????????? contribution = <0>;
??????????????????????? trip = <&cpu_trip2>;
??????????????????????? cooling-device = <&cpu_budget_cooling 3 3>;
??????????????????? };
??????????????????? bind3{
??????????????????????? contribution = <0>;
??????????????????????? trip = <&cpu_trip3>;
??????????????????????? cooling-device = <&cpu_budget_cooling 4 5>;
??????????????????? };
??????????????????? bind4{
??????????????????????? contribution = <0>;
??????????????????????? trip = <&cpu_trip4>;
??????????????????????? cooling-device = <&cpu_budget_cooling 6 6>;
??????????????????? };
??????????????? };
??????????? };
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內(nèi)核使用thermal_zone_device 抽象獲取溫度的device.
struct thermal_zone_device {
??? int id;
??? char type[THERMAL_NAME_LENGTH];
??? struct device device;
??? struct thermal_attr *trip_temp_attrs;
??? struct thermal_attr *trip_type_attrs;
??? struct thermal_attr *trip_hyst_attrs;
??? void *devdata;
??? int trips;
??? int passive_delay;
??? int polling_delay;
??? int temperature;
??? int last_temperature;
??? int emul_temperature;
??? int passive;
??? unsigned int forced_passive;
??? struct thermal_zone_device_ops *ops;
??? const struct thermal_zone_params *tzp;
??? struct thermal_governor *governor;
??? struct list_head thermal_instances;
??? struct idr idr;
??? struct mutex lock; /* protect thermal_instances list */
??? struct list_head node;
??? struct delayed_work poll_queue;
}
struct thermal_zone_device_ops {
??? int (*bind) (struct thermal_zone_device *,
???????????? struct thermal_cooling_device *);
??? int (*unbind) (struct thermal_zone_device *,
?????????????? struct thermal_cooling_device *);
??? int (*get_temp) (struct thermal_zone_device *, int *);
??? int (*get_mode) (struct thermal_zone_device *,
???????????? enum thermal_device_mode *);
??? int (*set_mode) (struct thermal_zone_device *,
??????? enum thermal_device_mode);
??? int (*get_trip_type) (struct thermal_zone_device *, int,
??????? enum thermal_trip_type *);
??? int (*get_trip_temp) (struct thermal_zone_device *, int,
??????????????? int *);
??? int (*set_trip_temp) (struct thermal_zone_device *, int,
??????????????? int);
??? int (*get_trip_hyst) (struct thermal_zone_device *, int,
??????????????? int *);
??? int (*set_trip_hyst) (struct thermal_zone_device *, int,
??????????????? int);
??? int (*get_crit_temp) (struct thermal_zone_device *, int *);
??? int (*set_emul_temp) (struct thermal_zone_device *, int);
??? int (*get_trend) (struct thermal_zone_device *, int,
????????????? enum thermal_trend *);
??? int (*notify) (struct thermal_zone_device *, int,
?????????????? enum thermal_trip_type);
}
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thermal governal
降溫策略一個抽象，與cpufreq的governal概念類似。
內(nèi)核已經(jīng)實現(xiàn)了一些策略，step_wise, user_space, power_allocator, bang_bang 。我們常用step_wise。
/**
?* struct thermal_governor - structure that holds thermal governor information
?* @name:?????? name of the governor
?* @throttle:?? callback called for every trip point even if temperature is
?*????????????? below the trip point temperature
?* @governor_list:????? node in thermal_governor_list (in thermal_core.c)
?*/
struct thermal_governor {
??????? char name[THERMAL_NAME_LENGTH];
??? /* 策略函數(shù) */
??????? int (*throttle)(struct thermal_zone_device *tz, int trip);
??????? struct list_head??????? governor_list;
};
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thermal cooling device
Thermal Cooling Device 是可以降溫設(shè)備的抽象，能降溫的設(shè)備比如風(fēng)扇，這些好理解，但是想 CPU,GPU 這些 Cooling devices 怎么理解呢？
其實降溫可以從兩方面來理解，一個是加快散熱，另外一個就是降低產(chǎn)熱量。風(fēng)扇，散熱片這些是用來加快散熱，CPU,GPU 這些 Cooling devices 是通過降低產(chǎn)熱來降溫。
struct thermal_cooling_device {
??? int id;
??????? char type[THERMAL_NAME_LENGTH];
??????? struct device device;
??????? struct device_node *np;
??????? void *devdata;
??? /* cooling device 操作函數(shù) */
??????? 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;
};
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 *);
??? /* 設(shè)定等級 */
??????? int (*set_cur_state) (struct thermal_cooling_device *, unsigned long);
};
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thermal core
Thermal Core作為中樞注冊Governor，注冊Thermal類，并且基于Device Tree注冊Thermal Zone；提供Thermal Zone注冊函數(shù)、Cooling Device注冊函數(shù)、提供將Cooling設(shè)備綁定到Zone的函數(shù)，一個Thermal Zone可以有多個Cooling設(shè)備；同時還提供一個核心函數(shù)thermal_zone_device_update作為Thermal中斷處理函數(shù)和輪詢函數(shù)，輪詢時間會根據(jù)不同Trip Delay調(diào)節(jié)。
模塊流程圖如下：
操作時序圖如下：

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