161 lines
6.6 KiB
Plaintext
161 lines
6.6 KiB
Plaintext
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Qualcomm QPNP PWM/LPG controller
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qpnp-pwm driver supports Pulse Width Module (PWM) functionality. PWM feature is
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used in range of applications such as varying Display brightness, LED dimming,
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etc. The Qualcomm PMICs have a physical device called Light Pulse Generator
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(LPG). In addition to support PWM functionality, the LPG module provides
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a rich set of user defined PWM pattern configurations, such as sawtooth, linear
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up, linear down, triangular patterns etc. The PWM patterns are used in
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applications such as charger driver where the driver uses these patterns
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to indicate various states of charging.
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Required device bindings:
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- compatible: should be "qcom,qpnp-pwm"
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- reg: Offset and length of the controller's LPG channel register,
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and LPG look-up table (LUT). The LPG look-up table is a
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contiguous address space that is populated with PWM values.
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The size of PWM value is 9 bit and the size of each
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entry of the table is 8 bit. Thus, two entries are used
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to fill each PWM value. The lower entry is used for PWM
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LSB byte and higher entry is used for PWM MSB bit.
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- reg-names: Names for the above registers.
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"qpnp-lpg-channel-base" = physical base address of the
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controller's LPG channel register.
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"qpnp-lpg-lut-base" = physical base address of LPG LUT.
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- qcom,channel-id: channel Id for the PWM.
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Optional device bindings:
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- qcom,channel-owner: A string value to supply owner information.
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- qcom,mode-select: 0 = PWM mode
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1 = LPG mode
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If this binding is specified along with the required bindings of PWM/LPG then
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in addition to configure PWM/LPG the qpnp-pwm driver also enables the feature
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at the probe time. In the case where the binding is not specified the qpnp-pwm
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driver does not enable the feature. Also, it is considered an error to specify
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a particular mode using this binding but not the respective feature subnode.
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All PWM devices support both PWM and LPG features within the same device.
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To support each feature, there are some required and optional bindings passed
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through device tree.
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The PWM device can enable one feature (either PWM or LPG) at any given time.
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Therefore, the qpnp-pwm driver applies the last PWM or LPG feature configuration
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and enables that feature.
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Required bindings to support PWM feature:
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- qcom,period: PWM period time in microseconds.
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- qcom,duty: PWM duty time in microseconds.
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- label: "pwm"
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Required bindings to support LPG feature:
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The following bindings are needed to configure LPG mode, where a list of
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duty cycle percentages is populated. The size of the list cannot exceed
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the size of the LPG look-up table.
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- qcom,period: PWM period time in microseconds.
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- qcom,duty-percents: List of entries for look-up table
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- cell-index: Index of look-up table that should be used to start
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filling up the duty-pct list. start-idx + size of list
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cannot exceed the size of look-up table.
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- label: "lpg"
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Optional bindings to support LPG feature:
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- qcom,ramp-step-duration: Time (in ms) to wait before loading next entry of LUT
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- qcom,lpg-lut-pause-hi: Time (in ms) to wait once pattern reaches to hi
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index.
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- qcom,lpg-lut-pause-lo: Time (in ms) to wait once pattern reaches to lo
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index.
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- qcom,lpg-lut-ramp-direction: 1 = Start the pattern from lo index to hi index.
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0 = Start the pattern from hi index to lo index.
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- qcom,lpg-lut-pattern-repeat: 1 = Repeat the pattern after the pause once it
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reaches to last duty cycle.
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0 = Do not repeat the pattern.
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- qcom,lpg-lut-ramp-toggle: 1 = Toggle the direction of the pattern.
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0 = Do not toggle the direction.
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- qcom,lpg-lut-enable-pause-hi: 1 = Enable pause time at hi index.
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0 = Disable pause time at hi index.
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- qcom,lpg-lut-enable-pause-lo: 1 = Enable pause time at lo index.
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0 = Disable pause time at lo index.
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Example:
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qcom,spmi@fc4c0000 {
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#address-cells = <1>;
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#size-cells = <0>;
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qcom,pm8941@1 {
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spmi-slave-container;
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reg = <0x1>;
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#address-cells = <1>;
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#size-cells = <1>;
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pwm@b100 {
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#address-cells = <1>;
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#size-cells = <1>;
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compatible = "qcom,qpnp-pwm";
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reg = <0xb100 0x100>,
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<0xb040 0x80>;
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reg-names = "qpnp-lpg-channel-base", "qpnp-lpg-lut-base";
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qcom,channel-id = <0>;
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status = "okay";
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};
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pwm@b200 {
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#address-cells = <1>;
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#size-cells = <1>;
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compatible = "qcom,qpnp-pwm";
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reg = <0xb200 0x100>,
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<0xb040 0x80>;
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reg-names = "qpnp-lpg-channel-base", "qpnp-lpg-lut-base";
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qcom,channel-id = <1>;
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qcom,period = <6000000>;
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status = "okay";
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qcom,pwm {
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qcom,duty = <4000000>;
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label = "pwm";
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};
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};
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pwm@b500 {
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#address-cells = <1>;
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#size-cells = <1>;
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compatible = "qcom,qpnp-pwm";
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reg = <0xb500 0x100>,
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<0xb040 0x80>;
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reg-names = "qpnp-lpg-channel-base", "qpnp-lpg-lut-base";
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qcom,channel-id = <4>;
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qcom,period = <6000000>;
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qcom,mode-select = <0>;
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qcom,channel-owner = "RGB-led";
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status = "okay";
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qcom,pwm {
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qcom,duty = <4000000>;
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label = "pwm";
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};
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qcom,lpg {
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qcom,duty-percents = <1 14 28 42 56 84 100
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100 84 56 42 28 14 1>;
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cell-index = <0>;
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qcom,ramp-step-duration = <20>;
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label = "lpg";
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};
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};
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};
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};
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There are couple of ways to configure PWM device channels as shown in above
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example,
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1. The PWM device channel #0 is configured with only required device bindings.
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In this case, the qpnp-pwm driver does not configure any mode by default.
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2. The qpnp-pwm driver configures PWM device channel #1 with PWM feature
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configuration, but does not enable the channel since "qcom,mode-select" binding
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is not specified in the devicetree.
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3. Both the PWM and LPG configurations are provided for PWM device channel #4.
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The qpnp-pwm driver configures both the modes, but enables PWM mode at the probe
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time. It also sets the channel owner information for the channel.
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