70 lines
2.0 KiB
Plaintext
70 lines
2.0 KiB
Plaintext
Specifying PWM information for devices
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======================================
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1) PWM user nodes
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-----------------
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PWM users should specify a list of PWM devices that they want to use
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with a property containing a 'pwm-list':
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pwm-list ::= <single-pwm> [pwm-list]
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single-pwm ::= <pwm-phandle> <pwm-specifier>
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pwm-phandle : phandle to PWM controller node
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pwm-specifier : array of #pwm-cells specifying the given PWM
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(controller specific)
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PWM properties should be named "pwms". The exact meaning of each pwms
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property must be documented in the device tree binding for each device.
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An optional property "pwm-names" may contain a list of strings to label
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each of the PWM devices listed in the "pwms" property. If no "pwm-names"
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property is given, the name of the user node will be used as fallback.
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Drivers for devices that use more than a single PWM device can use the
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"pwm-names" property to map the name of the PWM device requested by the
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pwm_get() call to an index into the list given by the "pwms" property.
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The following example could be used to describe a PWM-based backlight
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device:
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pwm: pwm {
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#pwm-cells = <2>;
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};
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[...]
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bl: backlight {
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pwms = <&pwm 0 5000000>;
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pwm-names = "backlight";
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};
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Note that in the example above, specifying the "pwm-names" is redundant
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because the name "backlight" would be used as fallback anyway.
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pwm-specifier typically encodes the chip-relative PWM number and the PWM
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period in nanoseconds.
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Optionally, the pwm-specifier can encode a number of flags (defined in
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<dt-bindings/pwm/pwm.h>) in a third cell:
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- PWM_POLARITY_INVERTED: invert the PWM signal polarity
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Example with optional PWM specifier for inverse polarity
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bl: backlight {
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pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED>;
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pwm-names = "backlight";
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};
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2) PWM controller nodes
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-----------------------
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PWM controller nodes must specify the number of cells used for the
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specifier using the '#pwm-cells' property.
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An example PWM controller might look like this:
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pwm: pwm@7000a000 {
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compatible = "nvidia,tegra20-pwm";
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reg = <0x7000a000 0x100>;
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#pwm-cells = <2>;
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};
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