本文部分内容参考Linux Thermal 学习笔记 - 爱码网。特此致谢！

接前一篇文章Linux内核Thermal框架详解三、Thermal Core（2）

三、相关源码及分析

2. thermal_register_governors

原本thermal_register_governors属于下一级函数，在前篇文章已经介绍过了。但是由于其重要性，因此将它提升一级，并且在本篇文章中进行更详细解析。再次列出函数源码，位于drivers/thermal/thermal_core.c中，如下所示：

static void __init thermal_unregister_governors(void)
{struct thermal_governor **governor;for_each_governor_table(governor)thermal_unregister_governor(*governor);
}static int __init thermal_register_governors(void)
{int ret = 0;struct thermal_governor **governor;for_each_governor_table(governor) {ret = thermal_register_governor(*governor);if (ret) {pr_err("Failed to register governor: '%s'",(*governor)->name);break;}pr_info("Registered thermal governor '%s'",(*governor)->name);}if (ret) {struct thermal_governor **gov;for_each_governor_table(gov) {if (gov == governor)break;thermal_unregister_governor(*gov);}}return ret;
}

thermal_register_governor函数的总体功能是将所有的governor策略（step_wise、power_alloctor、user_space、fair_share等）默认都注册给kernel。

下边对于关键代码进行分析。

（1）for_each_governor_table

for_each_governor_table是一个宏定义，在drivers/thermal/thermal_core.h中，代码如下：

#define for_each_governor_table(__governor)		\for (__governor = __governor_thermal_table;	\__governor < __governor_thermal_table_end;	\__governor++)

__governor_thermal_table的定义直接搜索是找不到的，只是在同文件中有一个extern的引用。如下所示：

extern struct thermal_governor *__governor_thermal_table[];
extern struct thermal_governor *__governor_thermal_table_end[];

那么__governor_thermal_table的定义到底在什么地方？这得从THERMAL_TABLE宏说起。

THERMAL_TABLE宏在include/asm-generic/vmlinux.lds.h中，代码如下：

#ifdef CONFIG_THERMAL
#define THERMAL_TABLE(name)						\. = ALIGN(8);							\__##name##_thermal_table = .;					\KEEP(*(__##name##_thermal_table))				\__##name##_thermal_table_end = .;
#else
#define THERMAL_TABLE(name)
#endif

在配置了THERMAL选项的时候，才会有内容。假设有这样的定义THERMAL_TABLE(governor)，那么实际展开来，代码为：

. = ALIGN(8);							\
__governor_thermal_table = .;			\
KEEP(*(__governor_thermal_table))		\
__governor_thermal_table_end = .;

看到我们要找的__governor_thermal_table了吧，就是在这里最终出现了。

到此，还有一个问题没有弄清楚：我们上边是假设有THERMAL_TABLE(governor)的代码，那么真正调用THERMAL_TABLE宏的代码在哪里？

其实是在同文件（include/asm-generic/vmlinux.lds.h）中，代码如下：

/* init and exit section handling */
#define INIT_DATA							\KEEP(*(SORT(___kentry+*)))					\*(.init.data init.data.*)					\MEM_DISCARD(init.data*)						\KERNEL_CTORS()							\MCOUNT_REC()							\*(.init.rodata .init.rodata.*)					\FTRACE_EVENTS()							\TRACE_SYSCALLS()						\KPROBE_BLACKLIST()						\ERROR_INJECT_WHITELIST()					\MEM_DISCARD(init.rodata)					\CLK_OF_TABLES()							\RESERVEDMEM_OF_TABLES()						\TIMER_OF_TABLES()						\CPU_METHOD_OF_TABLES()						\CPUIDLE_METHOD_OF_TABLES()					\KERNEL_DTB()							\IRQCHIP_OF_MATCH_TABLE()					\ACPI_PROBE_TABLE(irqchip)					\ACPI_PROBE_TABLE(timer)						\THERMAL_TABLE(governor)						\EARLYCON_TABLE()						\LSM_TABLE()							\EARLY_LSM_TABLE()						\KUNIT_TABLE()

看到代码中的THERMAL_TABLE(governer)了吧，就是在这里。至于在哪里调用的INIT_DATA宏，在此就不再刨根问底了，毕竟不是本文的重点。

回到for_each_governor_table代码中，在弄清楚了全部细节之后，接着往下看整个代码段：

for_each_governor_table(governor) {ret = thermal_register_governor(*governor);if (ret) {pr_err("Failed to register governor: '%s'",(*governor)->name);break;}pr_info("Registered thermal governor '%s'",(*governor)->name);
}

展开：

for (__governor = __governor_thermal_table;	\__governor < __governor_thermal_table_end;	\__governor++) {ret = thermal_register_governor(*governor);if (ret) {pr_err("Failed to register governor: '%s'",(*governor)->name);break;}pr_info("Registered thermal governor '%s'",(*governor)->name);
}

这段代码的意思就比较明显了，遍历__governor_thermal_table中的每一项，进行注册。那么__governor_thermal_table中都包括了哪些项？又是什么时候加入进去的？且听我慢慢道来……

实际上，各个governor是通过 __section() 属性配合链接器脚本链接到一起的。以step_wise为例进行说明。

在drivers/thermal/gov_step_wise.c中有这样一行代码：

static struct thermal_governor thermal_gov_step_wise = {.name		= "step_wise",.throttle	= step_wise_throttle,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_step_wise);

THERMAL_GOVERNOR_DECLARE同样是宏，也是在drivers/thermal/thermal_core.h中，如下所示：

#define THERMAL_TABLE_ENTRY(table, name)			\static typeof(name) *__thermal_table_entry_##name	\__used __section("__" #table "_thermal_table") = &name#define THERMAL_GOVERNOR_DECLARE(name)	THERMAL_TABLE_ENTRY(governor, name)

上边代码连同进一步的宏定义一起写出了。因此，完全展开来就是：

static typeof(thermal_gov_step_wise) *__thermal_table_entry_thermal_gov_step_wise __used __section("__governor_thermal_table") = &thermal_gov_step_wise

由于thermal_gov_step_wise的类型为struct thermal_governor，因此，最终展开为：

static struct thermal_governor *__thermal_table_entry_thermal_gov_step_wise    \__used __section("__governor_thermal_table") = &thermal_gov_step_wise

这样，就完成了在__governor_thermal_table中添加一项thermal_gov_step_wise。

对于其它几种governor来说，都是同样的方法。在此，为了能够解析得更清晰、更彻底，列出全部的governor。

power_allocator在drivers/thermal/gov_power_allocator.c中：

static struct thermal_governor thermal_gov_power_allocator = {.name		= "power_allocator",.bind_to_tz	= power_allocator_bind,.unbind_from_tz	= power_allocator_unbind,.throttle	= power_allocator_throttle,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_power_allocator);

展开为：

static struct thermal_governor *__thermal_table_entry_thermal_gov_power_allocator    \__used __section("__governor_thermal_table") = &thermal_gov_power_allocator

fair_share在drivers/thermal/gov_fair_share.c中：

static struct thermal_governor thermal_gov_fair_share = {.name		= "fair_share",.throttle	= fair_share_throttle,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_fair_share);

展开为：

static struct thermal_governor *__thermal_table_entry_thermal_gov_fair_share    \__used __section("__governor_thermal_table") = &thermal_gov_fair_share

user_space在drivers/thermal/gov_user_space.c中：

static struct thermal_governor thermal_gov_user_space = {.name		= "user_space",.throttle	= notify_user_space,.bind_to_tz	= user_space_bind,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_user_space);

展开为：

static struct thermal_governor *__thermal_table_entry_thermal_gov_user_space    \__used __section("__governor_thermal_table") = &thermal_gov_user_space

bang_bang在drivers/thermal/gov_bang_bang.c中：

static struct thermal_governor thermal_gov_bang_bang = {.name		= "bang_bang",.throttle	= bang_bang_control,
};
THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);

展开为：

static struct thermal_governor *__thermal_table_entry_thermal_gov_bang_bang    \__used __section("__governor_thermal_table") = &thermal_gov_bang_bang

欲知后事如何，且听下回分解。