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diff --git a/Documentation/power/regulator/consumer.rst b/Documentation/power/regulator/consumer.rst new file mode 100644 index 000000000..0cd8cc127 --- /dev/null +++ b/Documentation/power/regulator/consumer.rst @@ -0,0 +1,229 @@ +=================================== +Regulator Consumer Driver Interface +=================================== + +This text describes the regulator interface for consumer device drivers. +Please see overview.txt for a description of the terms used in this text. + + +1. Consumer Regulator Access (static & dynamic drivers) +======================================================= + +A consumer driver can get access to its supply regulator by calling :: + + regulator = regulator_get(dev, "Vcc"); + +The consumer passes in its struct device pointer and power supply ID. The core +then finds the correct regulator by consulting a machine specific lookup table. +If the lookup is successful then this call will return a pointer to the struct +regulator that supplies this consumer. + +To release the regulator the consumer driver should call :: + + regulator_put(regulator); + +Consumers can be supplied by more than one regulator e.g. codec consumer with +analog and digital supplies :: + + digital = regulator_get(dev, "Vcc"); /* digital core */ + analog = regulator_get(dev, "Avdd"); /* analog */ + +The regulator access functions regulator_get() and regulator_put() will +usually be called in your device drivers probe() and remove() respectively. + + +2. Regulator Output Enable & Disable (static & dynamic drivers) +=============================================================== + + +A consumer can enable its power supply by calling:: + + int regulator_enable(regulator); + +NOTE: + The supply may already be enabled before regulator_enabled() is called. + This may happen if the consumer shares the regulator or the regulator has been + previously enabled by bootloader or kernel board initialization code. + +A consumer can determine if a regulator is enabled by calling:: + + int regulator_is_enabled(regulator); + +This will return > zero when the regulator is enabled. + + +A consumer can disable its supply when no longer needed by calling:: + + int regulator_disable(regulator); + +NOTE: + This may not disable the supply if it's shared with other consumers. The + regulator will only be disabled when the enabled reference count is zero. + +Finally, a regulator can be forcefully disabled in the case of an emergency:: + + int regulator_force_disable(regulator); + +NOTE: + this will immediately and forcefully shutdown the regulator output. All + consumers will be powered off. + + +3. Regulator Voltage Control & Status (dynamic drivers) +======================================================= + +Some consumer drivers need to be able to dynamically change their supply +voltage to match system operating points. e.g. CPUfreq drivers can scale +voltage along with frequency to save power, SD drivers may need to select the +correct card voltage, etc. + +Consumers can control their supply voltage by calling:: + + int regulator_set_voltage(regulator, min_uV, max_uV); + +Where min_uV and max_uV are the minimum and maximum acceptable voltages in +microvolts. + +NOTE: this can be called when the regulator is enabled or disabled. If called +when enabled, then the voltage changes instantly, otherwise the voltage +configuration changes and the voltage is physically set when the regulator is +next enabled. + +The regulators configured voltage output can be found by calling:: + + int regulator_get_voltage(regulator); + +NOTE: + get_voltage() will return the configured output voltage whether the + regulator is enabled or disabled and should NOT be used to determine regulator + output state. However this can be used in conjunction with is_enabled() to + determine the regulator physical output voltage. + + +4. Regulator Current Limit Control & Status (dynamic drivers) +============================================================= + +Some consumer drivers need to be able to dynamically change their supply +current limit to match system operating points. e.g. LCD backlight driver can +change the current limit to vary the backlight brightness, USB drivers may want +to set the limit to 500mA when supplying power. + +Consumers can control their supply current limit by calling:: + + int regulator_set_current_limit(regulator, min_uA, max_uA); + +Where min_uA and max_uA are the minimum and maximum acceptable current limit in +microamps. + +NOTE: + this can be called when the regulator is enabled or disabled. If called + when enabled, then the current limit changes instantly, otherwise the current + limit configuration changes and the current limit is physically set when the + regulator is next enabled. + +A regulators current limit can be found by calling:: + + int regulator_get_current_limit(regulator); + +NOTE: + get_current_limit() will return the current limit whether the regulator + is enabled or disabled and should not be used to determine regulator current + load. + + +5. Regulator Operating Mode Control & Status (dynamic drivers) +============================================================== + +Some consumers can further save system power by changing the operating mode of +their supply regulator to be more efficient when the consumers operating state +changes. e.g. consumer driver is idle and subsequently draws less current + +Regulator operating mode can be changed indirectly or directly. + +Indirect operating mode control. +-------------------------------- +Consumer drivers can request a change in their supply regulator operating mode +by calling:: + + int regulator_set_load(struct regulator *regulator, int load_uA); + +This will cause the core to recalculate the total load on the regulator (based +on all its consumers) and change operating mode (if necessary and permitted) +to best match the current operating load. + +The load_uA value can be determined from the consumer's datasheet. e.g. most +datasheets have tables showing the maximum current consumed in certain +situations. + +Most consumers will use indirect operating mode control since they have no +knowledge of the regulator or whether the regulator is shared with other +consumers. + +Direct operating mode control. +------------------------------ + +Bespoke or tightly coupled drivers may want to directly control regulator +operating mode depending on their operating point. This can be achieved by +calling:: + + int regulator_set_mode(struct regulator *regulator, unsigned int mode); + unsigned int regulator_get_mode(struct regulator *regulator); + +Direct mode will only be used by consumers that *know* about the regulator and +are not sharing the regulator with other consumers. + + +6. Regulator Events +=================== + +Regulators can notify consumers of external events. Events could be received by +consumers under regulator stress or failure conditions. + +Consumers can register interest in regulator events by calling:: + + int regulator_register_notifier(struct regulator *regulator, + struct notifier_block *nb); + +Consumers can unregister interest by calling:: + + int regulator_unregister_notifier(struct regulator *regulator, + struct notifier_block *nb); + +Regulators use the kernel notifier framework to send event to their interested +consumers. + +7. Regulator Direct Register Access +=================================== + +Some kinds of power management hardware or firmware are designed such that +they need to do low-level hardware access to regulators, with no involvement +from the kernel. Examples of such devices are: + +- clocksource with a voltage-controlled oscillator and control logic to change + the supply voltage over I2C to achieve a desired output clock rate +- thermal management firmware that can issue an arbitrary I2C transaction to + perform system poweroff during overtemperature conditions + +To set up such a device/firmware, various parameters like I2C address of the +regulator, addresses of various regulator registers etc. need to be configured +to it. The regulator framework provides the following helpers for querying +these details. + +Bus-specific details, like I2C addresses or transfer rates are handled by the +regmap framework. To get the regulator's regmap (if supported), use:: + + struct regmap *regulator_get_regmap(struct regulator *regulator); + +To obtain the hardware register offset and bitmask for the regulator's voltage +selector register, use:: + + int regulator_get_hardware_vsel_register(struct regulator *regulator, + unsigned *vsel_reg, + unsigned *vsel_mask); + +To convert a regulator framework voltage selector code (used by +regulator_list_voltage) to a hardware-specific voltage selector that can be +directly written to the voltage selector register, use:: + + int regulator_list_hardware_vsel(struct regulator *regulator, + unsigned selector); |