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