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| -rw-r--r-- | doc/device-tree-bindings/pwm/pwm.txt | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/doc/device-tree-bindings/pwm/pwm.txt b/doc/device-tree-bindings/pwm/pwm.txt new file mode 100644 index 00000000000..8556263b850 --- /dev/null +++ b/doc/device-tree-bindings/pwm/pwm.txt @@ -0,0 +1,69 @@ +Specifying PWM information for devices +====================================== + +1) PWM user nodes +----------------- + +PWM users should specify a list of PWM devices that they want to use +with a property containing a 'pwm-list': + + pwm-list ::= <single-pwm> [pwm-list] + single-pwm ::= <pwm-phandle> <pwm-specifier> + pwm-phandle : phandle to PWM controller node + pwm-specifier : array of #pwm-cells specifying the given PWM + (controller specific) + +PWM properties should be named "pwms". The exact meaning of each pwms +property must be documented in the device tree binding for each device. +An optional property "pwm-names" may contain a list of strings to label +each of the PWM devices listed in the "pwms" property. If no "pwm-names" +property is given, the name of the user node will be used as fallback. + +Drivers for devices that use more than a single PWM device can use the +"pwm-names" property to map the name of the PWM device requested by the +pwm_get() call to an index into the list given by the "pwms" property. + +The following example could be used to describe a PWM-based backlight +device: + + pwm: pwm { + #pwm-cells = <2>; + }; + + [...] + + bl: backlight { + pwms = <&pwm 0 5000000>; + pwm-names = "backlight"; + }; + +Note that in the example above, specifying the "pwm-names" is redundant +because the name "backlight" would be used as fallback anyway. + +pwm-specifier typically encodes the chip-relative PWM number and the PWM +period in nanoseconds. + +Optionally, the pwm-specifier can encode a number of flags (defined in +<dt-bindings/pwm/pwm.h>) in a third cell: +- PWM_POLARITY_INVERTED: invert the PWM signal polarity + +Example with optional PWM specifier for inverse polarity + + bl: backlight { + pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED>; + pwm-names = "backlight"; + }; + +2) PWM controller nodes +----------------------- + +PWM controller nodes must specify the number of cells used for the +specifier using the '#pwm-cells' property. + +An example PWM controller might look like this: + + pwm: pwm@7000a000 { + compatible = "nvidia,tegra20-pwm"; + reg = <0x7000a000 0x100>; + #pwm-cells = <2>; + }; |