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    對於嵌入式裝置來說，合適的電源管理，不僅可以延長電池的壽命，而且可以省電，延長裝置執行時間，在提高使用者體驗方面有很大的好處。所以，各個soc廠家在這方面花了很多的功夫。下面，我們可以看看linux是如何處理電源管理驅動的。

1、程式碼目錄

drivers/regulator

2、檢視目錄下的Kconfig檔案

menuconfig REGULATOR
	bool "Voltage and Current Regulator Support"
	help
	  Generic Voltage and Current Regulator support.

	  This framework is designed to provide a generic interface to voltage
	  and current regulators within the Linux kernel. It's intended to
	  provide voltage and current control to client or consumer drivers and
	  also provide status information to user space applications through a
	  sysfs interface.

	  The intention is to allow systems to dynamically control regulator
	  output in order to save power and prolong battery life. This applies
	  to both voltage regulators (where voltage output is controllable) and
	  current sinks (where current output is controllable).

	  This framework safely compiles out if not selected so that client
	  drivers can still be used in systems with no software controllable
	  regulators.

	  If unsure, say no.
 

3、閱讀檔案，得知REGULATOR是最核心的模組macro，那我們可以找一個裝置的macro看看

config REGULATOR_STM32_VREFBUF
	tristate "STMicroelectronics STM32 VREFBUF"
	depends on ARCH_STM32 || COMPILE_TEST
	help
	  This driver supports STMicroelectronics STM32 VREFBUF (voltage
	  reference buffer) which can be used as voltage reference for
	  internal ADCs, DACs and also for external components through
	  dedicated Vref+ pin.

	  This driver can also be built as a module. If so, the module
	  will be called stm32-vrefbuf.
 

4、沒有找到s3c，可以看一下stm32晶片的依賴屬性，接著看Makefile

obj-$(CONFIG_REGULATOR) += core.o dummy.o fixed-helper.o helpers.o devres.o
obj-$(CONFIG_OF) += of_regulator.o
obj-$(CONFIG_REGULATOR_FIXED_VOLTAGE) += fixed.o
obj-$(CONFIG_REGULATOR_VIRTUAL_CONSUMER) += virtual.o
obj-$(CONFIG_REGULATOR_USERSPACE_CONSUMER) += userspace-consumer.o

obj-$(CONFIG_REGULATOR_STM32_VREFBUF) += stm32-vrefbuf.o
 

5、看的出來stm32只依賴於stm32-verfbuf.c檔案，繼續檢視

static const struct of_device_id stm32_vrefbuf_of_match[] = {
	{ .compatible = "st,stm32-vrefbuf", },
	{},
};
MODULE_DEVICE_TABLE(of, stm32_vrefbuf_of_match);

static struct platform_driver stm32_vrefbuf_driver = {
	.probe = stm32_vrefbuf_probe,
	.remove = stm32_vrefbuf_remove,
	.driver = {
		.name  = "stm32-vrefbuf",
		.of_match_table = of_match_ptr(stm32_vrefbuf_of_match),
	},
};
module_platform_driver(stm32_vrefbuf_driver);

6、確認驅動為platform驅動，尋找regulator特有的資料結構

static const struct regulator_ops stm32_vrefbuf_volt_ops = {
	.enable		= stm32_vrefbuf_enable,
	.disable	= stm32_vrefbuf_disable,
	.is_enabled	= stm32_vrefbuf_is_enabled,
	.get_voltage_sel = stm32_vrefbuf_get_voltage_sel,
	.set_voltage_sel = stm32_vrefbuf_set_voltage_sel,
	.list_voltage	= regulator_list_voltage_table,
};

static const struct regulator_desc stm32_vrefbuf_regu = {
	.name = "vref",
	.supply_name = "vdda",
	.volt_table = stm32_vrefbuf_voltages,
	.n_voltages = ARRAY_SIZE(stm32_vrefbuf_voltages),
	.ops = &stm32_vrefbuf_volt_ops,
	.type = REGULATOR_VOLTAGE,
	.owner = THIS_MODULE,
};

7、由程式碼得知，regulator_ops和regulator_desc才是特有的regulator資料結構，當然也少不了註冊函式

	rdev = regulator_register(&stm32_vrefbuf_regu, &config);
	if (IS_ERR(rdev)) {
		ret = PTR_ERR(rdev);
		dev_err(&pdev->dev, "register failed with error %d\n", ret);
		goto err_clk_dis;
	}
	platform_set_drvdata(pdev, rdev);

8、進一步確認of_device_id是不是真實存在，可以在arch/arm/boot/dts/stm32h743.dtsi找到對應內容

		vrefbuf: [email protected] {
			compatible = "st,stm32-vrefbuf";
			reg = <0x58003C00 0x8>;
			clocks = <&rcc VREF_CK>;
			regulator-min-microvolt = <1500000>;
			regulator-max-microvolt = <2500000>;
			status = "disabled";
		};