转自蜗窝科技：http://www.wowotech.net/pm_subsystem/regulator_driver.html
说实话，这篇好难懂啊。。。
1. 前言
本文从regulator driver的角度，描述怎样基于regulator framework编写regulator驱动。同时，以此为契机，学习、理解regulator有关的物理特性，以便能够更好的使用它们。
2. regulator driver的实现步骤
2.1 确定系统中regulator有关的硬件组成
提起硬件，最好能有个例子，好在有device tree，一个活生生的硬件拓扑结构。这里以NVIDIA Tegra Dalmore A04开发板为例（regulator有关的device tree位于“arch\arm\boot\dts\tegra114-dalmore.dts”）：
这里的regulator结构是相当复杂的，其中彩色框代表最终的regulator抽象，它的前一级表示regulator的载体（可以是PMIC、CPU、等等）。下面将会详细说明：
a）CPU通过I2C controller，连接一个降压控制器（TI tps51632），该控制器输出名称为“vdd-cpu”的电压，就称作vdd-cpu regulator吧（因此，在kernel中，regulator是一个虚拟设备）。
b）CPU通过I2C controller，连接一个前端电源管理芯片（TI tps65090），该芯片除了具备充电管理功能外，内置了多个regulator，例如dcdc1、dcdc2等等。
c）CPU通过I2C controller，连接另一个电源管理芯片（TI tps65913），该芯片具有两个功能：GPIO输出和PMIC。PMIC内置了多个regulator，如vddio-ddr、vdd-core等等。
d）CPU内部也集成了一些regulator，如vdd_ac_bat等等。
这些思考在本文的例子（NVIDIA Tegra Dalmore A04的regulator）中体现尤为突出，它的本质是软件设计中的模块划分，从而决定了regulator在DTS中的呈现方式和层次。
2.2 使用DTS，将硬件拓扑呈现出来
1）tps51632（是一种电源管理模块）
tps51632是一个简单的器件，位于i2c总线下面，包含一个regulator器件，因此其DTS比较简单，如下：
1: /* arch\arm\boot\dts\tegra114-dalmore.dts */
2: i2c@7000d000 {
3: status = "okay";
4: clock-frequency = <400000>;
5:
6: tps51632@43 {
7: compatible = "ti,tps51632";
8: reg = <0x43>;
9: regulator-name = "vdd-cpu";
10: regulator-min-microvolt = <500000>;
11: regulator-max-microvolt = <1520000>;
12: regulator-boot-on;
13: regulator-always-on;
14: };
15: ...
16: }
i2c控制器的node为“i2c@7000d000”，tps51632是其下的一个子node，名称为“tps51632@43”，compatible为“ti,tps51632”。tps51632下面以“regulator-”为前缀的字段，是regulator特有的字段，后面会统一介绍。
注2：为什么“i2c@7000d000”中没有compatible字段？其实是有的，可参考“arch\arm\boot\dts\tegra114.dtsi”，DTC在编译DTS时，会将这两个文件中的node合并。
注3：kernel在初始化时，只会为二级node（即“/”下面的节点，本文的例子是“i2c@7000d000”）创建platform设备，至于三级node（这里的“tps51632@43”），则由其bus（i2c）创建。后面我们会遇到其它的情况，到时再介绍。
2）tps65090
tps65090相对比较复杂，它位于相同的i2c总线下面，但包含两个相对复杂的功能实体，charger和PMIC，我们看看其DTS怎么写的：
1: i2c@7000d000 {
2: status = "okay";
3: ...
4:
5: tps65090@48 {
6: compatible = "ti,tps65090";
7: reg = <0x48>;
8: ...
9:
10: charger: charger {
11: compatible = "ti,tps65090-charger";
12: ti,enable-low-current-chrg;
13: };
14:
15: regulators {
16: tps65090_dcdc1_reg: dcdc1 {
17: regulator-name = "vdd-sys-5v0";
18: regulator-always-on;
19: regulator-boot-on;
20: };
21:
22: tps65090_dcdc2_reg: dcdc2 {
23: regulator-name = "vdd-sys-3v3";
24: regulator-always-on;
25: regulator-boot-on;
26: };
27: ...
28: }
29: }
30: }
和tps51632类似，但它下面又包含了两个子node：charger和regulators。其中charger竟然还有compatible字段。
回忆一下上面“注3”，kernel只会为"i2c@7000d000”创建platform device，“tps65090@48”则由i2c core创建，那么它下面的子node呢？一定是tps65090 driver处理了，感兴趣的读者可以阅读“drivers/mfd/tps65090.c”、“drivers/power/tps65090-charger.c”和“drivers/regulator/tps65090-regulator.c”，这里面还涉及了MFD（multi-function device，多功能设备），很有意思。
回到本文的主题上，虽然这里的regulators没有compatible字段，也会创建相应的platform device（具体可参考“drivers/mfd/tps65090.c”），这从侧面回答了上面的一个思考：从物理范畴，tps65090是一个独立的设备，但它内部有两个功能模块，因此会存在两个platform device。
3）tps65913，和tps65090类似，不再介绍。
4）CPU中的regulator
这一类regulator比较特殊，直接集成在CPU内部，DTS如下：
1: regulators {
2: compatible = "simple-bus";
3: #address-cells = <1>;
4: #size-cells = <0>;
5:
6: vdd_ac_bat_reg: regulator@0 {
7: compatible = "regulator-fixed";
8: reg = <0>;
9: regulator-name = "vdd_ac_bat";
10: regulator-min-microvolt = <5000000>;
11: regulator-max-microvolt = <5000000>;
12: regulator-always-on;
13: };
14:
15: dvdd_ts_reg: regulator@1 {
16: compatible = "regulator-fixed";
17: reg = <1>;
18: regulator-name = "dvdd_ts";
19: regulator-min-microvolt = <1800000>;
20: regulator-max-microvolt = <1800000>;
21: enable-active-high;
22: gpio = <&gpio TEGRA_GPIO(H, 5) GPIO_ACTIVE_HIGH>;
23: };
24: ...
25: };
在回到刚才的话题上，kernel只为二级node创建platform device（这里的“regulators”），那三级node（一个个的regulator）呢？没有相对标准的bus帮它们创建怎么办？借助“simple-bus”，具体可以参考of_platform_bus_create（“Device Tree(三):代码分析”）。
另外，这里的例子比较简单，都是fixed regulator，regulator framework core可以帮忙实现fixed类型的regulator的驱动，后面会说明。
2.3 编写与DTS节点对应的driver
这些driver的存在形式是多种多样的，但所做的工作基本类似：
1）初始化regulator的宿主（如上面的tps5163、PMIC、等等），最终的目的是，通过宿主提供的接口，修改regulator的输出。
2）初始化用于描述regulator的静态信息（struct regulator_desc）和动态信息（struct regulator_config），并以这二者为参数，调用regulator_register接口，将regulator注册到kernel中。
3）静态信息中包含regulator的操作函数集（struct regulator_ops），后续regulator的控制，将会由regulator framework core直接调用这些回调函数完成。
4）后面的事情，例如sysfs attribute创建等，就交给regulator framework core了。
3. DTS相关的实现逻辑
3.1 DTS的内容
回忆一下“Linux Regulator Framework(1)_概述”中介绍的machine的主要功能：使用软件语言（struct regulator_init_data），静态的描述regulator在板级的物理现状。对regulator driver而言，DTS主要用于配置regulator的init data。先看一下struct regulator_init_data：
1: /**
2: * struct regulator_init_data - regulator platform initialisation data.
3: *
4: * Initialisation constraints, our supply and consumers supplies.
5: *
6: * @supply_regulator: Parent regulator. Specified using the regulator name
7: * as it appears in the name field in sysfs, which can
8: * be explicitly set using the constraints field 'name'.
9: *
10: * @constraints: Constraints. These must be specified for the regulator to
11: * be usable.
12: * @num_consumer_supplies: Number of consumer device supplies.
13: * @consumer_supplies: Consumer device supply configuration.
14: *
15: * @regulator_init: Callback invoked when the regulator has been registered.
16: * @driver_data: Data passed to regulator_init.
17: */
18: struct regulator_init_data {
19: const char *supply_regulator; /* or NULL for system supply */
20:
21: struct regulation_constraints constraints;
22:
23: int num_consumer_supplies;
24: struct regulator_consumer_supply *consumer_supplies;
25:
26: /* optional regulator machine specific init */
27: int (*regulator_init)(void *driver_data);
28: void *driver_data; /* core does not touch this */
29: };
supply_regulator，该regulator的前级regulator，一般在regulator driver中直接指定；
constraints，该regulator的使用限制，由DTS配置，并可以借助regulator core提供的辅助API（regulator_of_get_init_data）自动解析。后面会详细介绍；
num_consumer_supplies、consumer_supplies，使用该regulator的consumer的个数，及其设备名和supply名的map。用于建立consumer设备和regulator之间的关联，后面介绍consumer DTS时再详细说明；
regulator_init，regulator的init回调，由regulator driver提供，并在regulator注册时调用；
driver_data，保存driver的私有数据，并在调用regulator_init时传入。
看来DTS的内容都在struct regulation_constraints中，该结构保存了该regulator所有的物理限制，如下：
1: struct regulation_constraints {
2:
3: const char *name;
4:
5: /* voltage output range (inclusive) - for voltage control */
6: int min_uV;
7: int max_uV;
8:
9: int uV_offset;
10:
11: /* current output range (inclusive) - for current control */
12: int min_uA;
13: int max_uA;
14:
15: /* valid regulator operating modes for this machine */
16: unsigned int valid_modes_mask;
17:
18: /* valid operations for regulator on this machine */
19: unsigned int valid_ops_mask;
20:
21: /* regulator input voltage - only if supply is another regulator */
22: int input_uV;
23:
24: /* regulator suspend states for global PMIC STANDBY/HIBERNATE */
25: struct regulator_state state_disk;
26: struct regulator_state state_mem;
27: struct regulator_state state_standby;
28: suspend_state_t initial_state; /* suspend state to set at init */
29:
30: /* mode to set on startup */
31: unsigned int initial_mode;
32:
33: unsigned int ramp_delay;
34: unsigned int enable_time;
35:
36: /* constraint flags */
37: unsigned always_on:1; /* regulator never off when system is on */
38: unsigned boot_on:1; /* bootloader/firmware enabled regulator */
39: unsigned apply_uV:1; /* apply uV constraint if min == max */
40: unsigned ramp_disable:1; /* disable ramp delay */
41: };
3.2 DTS的解析
regulator的DTS信息，可以通过两种方法解析：
1）在regulator注册前，调用of_get_regulator_init_data接口自行解析，该接口的实现如下：
1: struct regulator_init_data *of_get_regulator_init_data(struct device *dev,
2: struct device_node *node)
3: {
4: struct regulator_init_data *init_data;
5:
6: if (!node)
7: return NULL;
8:
9: init_data = devm_kzalloc(dev, sizeof(*init_data), GFP_KERNEL);
10: if (!init_data)
11: return NULL; /* Out of memory? */
12:
13: of_get_regulation_constraints(node, &init_data);
14: return init_data;
15: }
16: EXPORT_SYMBOL_GPL(of_get_regulator_init_data);
该接口有两个输入参数：设备指针，以及包含了DTS信息的node指针（以3.1中的例子，即“tps51632@43”所在的node）。
它会分配一个struct regulator_init_data变量，并调用of_get_regulation_constraints解析DTS，把结果保存在该变量中。
最后返回struct regulator_init_data变量的地址。
2）在regulator注册时，由regulator_register调用regulator_of_get_init_data帮忙解析，该接口的实现如下：
1: struct regulator_init_data *regulator_of_get_init_data(struct device *dev,
2: const struct regulator_desc *desc,
3: struct device_node **node)
4: {
5: struct device_node *search, *child;
6: struct regulator_init_data *init_data = NULL;
7: const char *name;
8:
9: if (!dev->of_node || !desc->of_match)
10: return NULL;
11:
12: if (desc->regulators_node)
13: search = of_get_child_by_name(dev->of_node,
14: desc->regulators_node);
15: else
16: search = dev->of_node;
17:
18: if (!search) {
19: dev_dbg(dev, "Failed to find regulator container node '%s'\n",
20: desc->regulators_node);
21: return NULL;
22: }
23:
24: for_each_child_of_node(search, child) {
25: name = of_get_property(child, "regulator-compatible", NULL);
26: if (!name)
27: name = child->name;
28:
29: if (strcmp(desc->of_match, name))
30: continue;
31:
32: init_data = of_get_regulator_init_data(dev, child);
33: if (!init_data) {
34: dev_err(dev,
35: "failed to parse DT for regulator %s\n",
36: child->name);
37: break;
38: }
39:
40: of_node_get(child);
41: *node = child;
42: break;
43: }
44: of_node_put(search);
45:
46: return init_data;
47: }
与of_get_regulator_init_data不同的是，该接口以struct regulator_desc指针为参数，该参数提供了regulator DTS有关的搜索信息（desc->of_match），根据这些信息，可以获得包含regulator信息的DTS node。
它本质上是一种通用的DTS匹配逻辑（和kernel解析platform device的标准资源类似），大致如下：
a）调用者提供parent node（struct device指针中，代表regulators的宿主设备，如上面的tps65090@48），以及该regulator在DTS中的名称（由desc->of_match提供）。
b）还可以在struct regulator_desc中提供包含regulator DTS信息的node名称（可选，用于regulator不直接在parent node下的情况）。
c）以parent device的node，或者指定的子node为基准，查找其下所有的node，如果node的名字或者“regulator-compatible”字段和desc->of_match匹配，则调用of_get_regulator_init_data从中解析DTS信息。
总结：1、2两种DTS解析的方法，各有优缺点：1直接，方便，容易理解，但会有冗余代码；2简洁，但需要regulator driver开发者非常熟悉解析的原理，并以此设计DTS和struct regulator_desc变量。大家可以根据实际情况，灵活使用。
4. 主要数据结构
4.1 struct regulator_desc
1: /* include/linux/regulator/driver.h */
2:
3: struct regulator_desc {
4: const char *name;
5: const char *supply_name;
6: const char *of_match;
7: const char *regulators_node;
8: int id;
9: bool continuous_voltage_range;
10: unsigned n_voltages;
11: const struct regulator_ops *ops;
12: int irq;
13: enum regulator_type type;
14: struct module *owner;
15:
16: unsigned int min_uV;
17: unsigned int uV_step;
18: unsigned int linear_min_sel;
19: int fixed_uV;
20: unsigned int ramp_delay;
21:
22: const struct regulator_linear_range *linear_ranges;
23: int n_linear_ranges;
24:
25: const unsigned int *volt_table;
26:
27: unsigned int vsel_reg;
28: unsigned int vsel_mask;
29: unsigned int apply_reg;
30: unsigned int apply_bit;
31: unsigned int enable_reg;
32: unsigned int enable_mask;
33: unsigned int enable_val;
34: unsigned int disable_val;
35: bool enable_is_inverted;
36: unsigned int bypass_reg;
37: unsigned int bypass_mask;
38: unsigned int bypass_val_on;
39: unsigned int bypass_val_off;
40:
41: unsigned int enable_time;
42:
43: unsigned int off_on_delay;
44: };
4.2 struct regulator_config
struct regulator_config保存了regulator的动态信息，所谓的动态信息，是指那些会在driver运行过程中改变、或者driver运行后才会确定的信息，如下：
1: struct regulator_config {
2: struct device *dev;
3: const struct regulator_init_data *init_data;
4: void *driver_data;
5: struct device_node *of_node;
6: struct regmap *regmap;
7:
8: int ena_gpio;
9: unsigned int ena_gpio_invert:1;
10: unsigned int ena_gpio_flags;
11: };
dev，对应的struct device指针。会在regulator_register时，由regulator core分配，保存在此，以便后续使用；
init_data，init data指针，在解析DTS后，保存在此，以便后续使用；
of_node，可以为空；
regmap，参考后续描述；
ena_gpio、ena_gpio_invert、ena_gpio_flags，控制regulator使能的GPIO及其active极性。
4.3 struct regulator_dev
struct regulator_dev是regulator设备的抽象，当driver以struct regulator_desc、struct regulator_config两个类型的参数，调用regulator_register将regulator注册到kernel之后，regulator就会分配一个struct regulator_dev变量，后续所有的regulator操作，都将以该变量为对象。
1: struct regulator_dev {
2: const struct regulator_desc *desc;
3: int exclusive;
4: u32 use_count;
5: u32 open_count;
6: u32 bypass_count;
7:
8: /* lists we belong to */
9: struct list_head list; /* list of all regulators */
10:
11: /* lists we own */
12: struct list_head consumer_list; /* consumers we supply */
13:
14: struct blocking_notifier_head notifier;
15: struct mutex mutex; /* consumer lock */
16: struct module *owner;
17: struct device dev;
18: struct regulation_constraints *constraints;
19: struct regulator *supply; /* for tree */
20: struct regmap *regmap;
21:
22: struct delayed_work disable_work;
23: int deferred_disables;
24:
25: void *reg_data; /* regulator_dev data */
26:
27: struct dentry *debugfs;
28:
29: struct regulator_enable_gpio *ena_pin;
30: unsigned int ena_gpio_state:1;
31:
32: /* time when this regulator was disabled last time */
33: unsigned long last_off_jiffy;
34: };
desc，保存了regulator静态描述信息的指针（从这个角度看，所谓的静态描述，其变量必须为全局变量）；
exclusive、use_count、open_count、bypass_count，一些状态记录；
constraints，保存了regulator的constraints指针；
supply，该regulator的supply；
等等。
5 实现逻辑分析
本章简单的分析一下regulator driver相关的实现逻辑。如果要理解有些逻辑，必须具备一些regulator的基础知识，因此在需要的时候，会穿插介绍这些知识。
5.1 regulator core的初始化
regulator core的初始化操作由regulator_init接口负责，主要工作包括：
1）注册regulator class（/sys/class/regulator/）。
2）注册用于调试的debugfs。
和power switch class、input class等类似，regulator framework也是一种class，可以称作regulator class。
5.2 regulator register
regulator的注册，由regulator_register/devm_regulator_register接口负责，如下：
1: /**
2: * regulator_register - register regulator
3: * @regulator_desc: regulator to register
4: * @config: runtime configuration for regulator
5: *
6: * Called by regulator drivers to register a regulator.
7: * Returns a valid pointer to struct regulator_dev on success
8: * or an ERR_PTR() on error.
9: */
10: struct regulator_dev *
11: regulator_register(const struct regulator_desc *regulator_desc,
12: const struct regulator_config *config)
13: {
14: const struct regulation_constraints *constraints = NULL;
15: const struct regulator_init_data *init_data;
16: static atomic_t regulator_no = ATOMIC_INIT(0);
17: struct regulator_dev *rdev;
18: struct device *dev;
19: int ret, i;
20: const char *supply = NULL;
21:
22: if (regulator_desc == NULL || config == NULL)
23: return ERR_PTR(-EINVAL);
24:
25: dev = config->dev;
26: WARN_ON(!dev);
27:
28: if (regulator_desc->name == NULL || regulator_desc->ops == NULL)
29: return ERR_PTR(-EINVAL);
30:
31: if (regulator_desc->type != REGULATOR_VOLTAGE &&
32: regulator_desc->type != REGULATOR_CURRENT)
33: return ERR_PTR(-EINVAL);
34:
35: /* Only one of each should be implemented */
36: WARN_ON(regulator_desc->ops->get_voltage &&
37: regulator_desc->ops->get_voltage_sel);
38: WARN_ON(regulator_desc->ops->set_voltage &&
39: regulator_desc->ops->set_voltage_sel);
40:
41: /* If we're using selectors we must implement list_voltage. */
42: if (regulator_desc->ops->get_voltage_sel &&
43: !regulator_desc->ops->list_voltage) {
44: return ERR_PTR(-EINVAL);
45: }
46: if (regulator_desc->ops->set_voltage_sel &&
47: !regulator_desc->ops->list_voltage) {
48: return ERR_PTR(-EINVAL);
49: }
50:
51: rdev = kzalloc(sizeof(struct regulator_dev), GFP_KERNEL);
52: if (rdev == NULL)
53: return ERR_PTR(-ENOMEM);
54:
55: init_data = regulator_of_get_init_data(dev, regulator_desc,
56: &rdev->dev.of_node);
57: if (!init_data) {
58: init_data = config->init_data;
59: rdev->dev.of_node = of_node_get(config->of_node);
60: }
61:
62: mutex_lock(®ulator_list_mutex);
63:
64: mutex_init(&rdev->mutex);
65: rdev->reg_data = config->driver_data;
66: rdev->owner = regulator_desc->owner;
67: rdev->desc = regulator_desc;
68: if (config->regmap)
69: rdev->regmap = config->regmap;
70: else if (dev_get_regmap(dev, NULL))
71: rdev->regmap = dev_get_regmap(dev, NULL);
72: else if (dev->parent)
73: rdev->regmap = dev_get_regmap(dev->parent, NULL);
74: INIT_LIST_HEAD(&rdev->consumer_list);
75: INIT_LIST_HEAD(&rdev->list);
76: BLOCKING_INIT_NOTIFIER_HEAD(&rdev->notifier);
77: INIT_DELAYED_WORK(&rdev->disable_work, regulator_disable_work);
78:
79: /* preform any regulator specific init */
80: if (init_data && init_data->regulator_init) {
81: ret = init_data->regulator_init(rdev->reg_data);
82: if (ret < 0)
83: goto clean;
84: }
85:
86: /* register with sysfs */
87: rdev->dev.class = ®ulator_class;
88: rdev->dev.parent = dev;
89: dev_set_name(&rdev->dev, "regulator.%d",
90: atomic_inc_return(®ulator_no) - 1);
91: ret = device_register(&rdev->dev);
92: if (ret != 0) {
93: put_device(&rdev->dev);
94: goto clean;
95: }
96:
97: dev_set_drvdata(&rdev->dev, rdev);
98:
99: if (config->ena_gpio && gpio_is_valid(config->ena_gpio)) {
100: ret = regulator_ena_gpio_request(rdev, config);
101: if (ret != 0) {
102: rdev_err(rdev, "Failed to request enable GPIO%d: %d\n",
103: config->ena_gpio, ret);
104: goto wash;
105: }
106:
107: if (config->ena_gpio_flags & GPIOF_OUT_INIT_HIGH)
108: rdev->ena_gpio_state = 1;
109:
110: if (config->ena_gpio_invert)
111: rdev->ena_gpio_state = !rdev->ena_gpio_state;
112: }
113:
114: /* set regulator constraints */
115: if (init_data)
116: constraints = &init_data->constraints;
117:
118: ret = set_machine_constraints(rdev, constraints);
119: if (ret < 0)
120: goto scrub;
121:
122: /* add attributes supported by this regulator */
123: ret = add_regulator_attributes(rdev);
124: if (ret < 0)
125: goto scrub;
126:
127: if (init_data && init_data->supply_regulator)
128: supply = init_data->supply_regulator;
129: else if (regulator_desc->supply_name)
130: supply = regulator_desc->supply_name;
131:
132: if (supply) {
133: struct regulator_dev *r;
134:
135: r = regulator_dev_lookup(dev, supply, &ret);
136:
137: if (ret == -ENODEV) {
138: /*
139: * No supply was specified for this regulator and
140: * there will never be one.
141: */
142: ret = 0;
143: goto add_dev;
144: } else if (!r) {
145: dev_err(dev, "Failed to find supply %s\n", supply);
146: ret = -EPROBE_DEFER;
147: goto scrub;
148: }
149:
150: ret = set_supply(rdev, r);
151: if (ret < 0)
152: goto scrub;
153:
154: /* Enable supply if rail is enabled */
155: if (_regulator_is_enabled(rdev)) {
156: ret = regulator_enable(rdev->supply);
157: if (ret < 0)
158: goto scrub;
159: }
160: }
161:
162: add_dev:
163: /* add consumers devices */
164: if (init_data) {
165: for (i = 0; i < init_data->num_consumer_supplies; i++) {
166: ret = set_consumer_device_supply(rdev,
167: init_data->consumer_supplies[i].dev_name,
168: init_data->consumer_supplies[i].supply);
169: if (ret < 0) {
170: dev_err(dev, "Failed to set supply %s\n",
171: init_data->consumer_supplies[i].supply);
172: goto unset_supplies;
173: }
174: }
175: }
176:
177: list_add(&rdev->list, ®ulator_list);
178:
179: rdev_init_debugfs(rdev);
180: out:
181: mutex_unlock(®ulator_list_mutex);
182: return rdev;
183:
184: unset_supplies:
185: unset_regulator_supplies(rdev);
186:
187: scrub:
188: if (rdev->supply)
189: _regulator_put(rdev->supply);
190: regulator_ena_gpio_free(rdev);
191: kfree(rdev->constraints);
192: wash:
193: device_unregister(&rdev->dev);
194: /* device core frees rdev */
195: rdev = ERR_PTR(ret);
196: goto out;
197:
198: clean:
199: kfree(rdev);
200: rdev = ERR_PTR(ret);
201: goto out;
202: }
203: EXPORT_SYMBOL_GPL(regulator_register);
View Code
主要工作包括：
22
49，检查参数的合法性。其中3549行，涉及到电压控制的方式，后面后详细说明；55~60，协助从DTS解析init data，如果解析不到，则使用config中的；
68~73，协助获取regulator的register map（有的话），并保存在register device指针中。regulator driver会在需要的时候使用（通常是在ops回调函数中）；
74~77，初始化一些全局变量，consumer_list用于保存所有的consumer，list用于将自己添加到一个全局的regulator链表（regulator_list）上，disable_work是用于disable regulator的work queue；
86~95，将regulator device注册到kernel；
99~112，申请regulator enable gpio（有的话），并将相应的信息保存在regulator device指针中；
114~120，将从DTS中解析的constraints，应用起来（这个过程比较复杂，就不介绍了，感兴趣的读者可以自行分析）；
123，根据regulator的操作函数集，注册相应的attribute（和PSY class类似）；
127~160，如果该regulator有supply，根据supply的名字，获取相应的regulator device指针，同时根据supply指针，分配一个struct regulator结构，保存在该regulator的supply指针中。最后，如果该regulator处于使能状态，则需要使能其supply（这些动作，需要以consumer的视角操作，因而需要一个struct regulator变量）；
162~175，add consumer devices，等到介绍consumer时，再详细描述。
注4：register map是kernel提供的一种管理寄存器的机制，特别是较为复杂的寄存器，如codec等。本文不会过多描述，如需要，会专门写一篇文章介绍该机制。
5.3 regulator的操作模式（operation mode）
regulator的主要功能，是输出电压/电流的调整（或改变）。由于模拟器件的特性，电压/电流的改变，是需要一定的时间的。对有些regulator而言，可以工作在不同的模式，这些模式有不同的改变速度，可想而知，较快的速度，有较大的功耗。下面是operation mode定义（位于include/linux/regulator/consumer.h中）：
1: /*
2: * Regulator operating modes.
3: *
4: * Regulators can run in a variety of different operating modes depending on
5: * output load. This allows further system power savings by selecting the
6: * best (and most efficient) regulator mode for a desired load.
7: *
8: * Most drivers will only care about NORMAL. The modes below are generic and
9: * will probably not match the naming convention of your regulator data sheet
10: * but should match the use cases in the datasheet.
11: *
12: * In order of power efficiency (least efficient at top).
13: *
14: * Mode Description
15: * FAST Regulator can handle fast changes in it's load.
16: * e.g. useful in CPU voltage & frequency scaling where
17: * load can quickly increase with CPU frequency increases.
18: *
19: * NORMAL Normal regulator power supply mode. Most drivers will
20: * use this mode.
21: *
22: * IDLE Regulator runs in a more efficient mode for light
23: * loads. Can be used for devices that have a low power
24: * requirement during periods of inactivity. This mode
25: * may be more noisy than NORMAL and may not be able
26: * to handle fast load switching.
27: *
28: * STANDBY Regulator runs in the most efficient mode for very
29: * light loads. Can be used by devices when they are
30: * in a sleep/standby state. This mode is likely to be
31: * the most noisy and may not be able to handle fast load
32: * switching.
33: *
34: * NOTE: Most regulators will only support a subset of these modes. Some
35: * will only just support NORMAL.
36: *
37: * These modes can be OR'ed together to make up a mask of valid register modes.
38: */
39:
40: #define REGULATOR_MODE_FAST 0x1
41: #define REGULATOR_MODE_NORMAL 0x2
42: #define REGULATOR_MODE_IDLE 0x4
43: #define REGULATOR_MODE_STANDBY 0x8
相应的，regulator framework提供了一些机制，用于operation mode的操作，包括：
1）struct regulation_constraints中用于表示初始模式的字段initial_mode。
2）regulator ops中的set_mode/get_mode回调函数。
5.4 电压操作的两种方式
kernel抽象了两种电压操作的方法：
1）直接操作电压，对应struct regulator_ops中的如下回调函数：
1: /* get/set regulator voltage */
2: int (*list_voltage) (struct regulator_dev *, unsigned selector);
3: int (*set_voltage) (struct regulator_dev *, int min_uV, int max_uV,
4: unsigned *selector);
5: int (*get_voltage) (struct regulator_dev *);
其中set_voltage用于将电压设置为min_uV和max_uV范围内、和min_uV最接近的电压。该接口可以返回一个selector参数，用于告知调用者，实际的电压值；
get_voltage，用于返回当前的电压值；
list_voltage，以selector为参数，获取对应的电压值。
注5：有关selector的描述，可参考下面的介绍。
2）selector的形式
regulator driver以selector的形式，反映电压值。selector是一个从0开始的整数，driver提供如下的接口：
1: /* enumerate supported voltages */
2: int (*list_voltage) (struct regulator_dev *, unsigned selector);
3:
4: int (*map_voltage)(struct regulator_dev *, int min_uV, int max_uV);
5: int (*set_voltage_sel) (struct regulator_dev *, unsigned selector);
6: int (*get_voltage_sel) (struct regulator_dev *);
list_voltage，上面已经介绍；
map_voltage，是和list_voltage相对的接口，用于将电压范围map成一个selector值；
set_voltage_sel/get_voltage_sel，以selector的形式，操作电压。
regulator driver可以根据实际情况，选择一种实现方式。
5.5 regulator framework提供的sysfs接口
根据regulator提供的ops情况，regulator framework可以通过sysfs提供多种attribute，它们位于/sys/class/regulator/.../目录下，数量相当多，这里就不一一描述了，具体可参考：
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-regulator
6. 后记
这篇文章写的相当纠结，相当混乱，我相信读者很难看懂……
