linux/Documentation/devicetree/bindings/pwm/pwm.txt
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   1Specifying PWM information for devices
   2======================================
   3
   41) PWM user nodes
   5-----------------
   6
   7PWM users should specify a list of PWM devices that they want to use
   8with a property containing a 'pwm-list':
   9
  10        pwm-list ::= <single-pwm> [pwm-list]
  11        single-pwm ::= <pwm-phandle> <pwm-specifier>
  12        pwm-phandle : phandle to PWM controller node
  13        pwm-specifier : array of #pwm-cells specifying the given PWM
  14                        (controller specific)
  15
  16PWM properties should be named "pwms". The exact meaning of each pwms
  17property must be documented in the device tree binding for each device.
  18An optional property "pwm-names" may contain a list of strings to label
  19each of the PWM devices listed in the "pwms" property. If no "pwm-names"
  20property is given, the name of the user node will be used as fallback.
  21
  22Drivers for devices that use more than a single PWM device can use the
  23"pwm-names" property to map the name of the PWM device requested by the
  24pwm_get() call to an index into the list given by the "pwms" property.
  25
  26The following example could be used to describe a PWM-based backlight
  27device:
  28
  29        pwm: pwm {
  30                #pwm-cells = <2>;
  31        };
  32
  33        [...]
  34
  35        bl: backlight {
  36                pwms = <&pwm 0 5000000>;
  37                pwm-names = "backlight";
  38        };
  39
  40Note that in the example above, specifying the "pwm-names" is redundant
  41because the name "backlight" would be used as fallback anyway.
  42
  43pwm-specifier typically encodes the chip-relative PWM number and the PWM
  44period in nanoseconds.
  45
  46Optionally, the pwm-specifier can encode a number of flags in a third cell:
  47- bit 0: PWM signal polarity (0: normal polarity, 1: inverse polarity)
  48
  49Example with optional PWM specifier for inverse polarity
  50
  51        bl: backlight {
  52                pwms = <&pwm 0 5000000 1>;
  53                pwm-names = "backlight";
  54        };
  55
  562) PWM controller nodes
  57-----------------------
  58
  59PWM controller nodes must specify the number of cells used for the
  60specifier using the '#pwm-cells' property.
  61
  62An example PWM controller might look like this:
  63
  64        pwm: pwm@7000a000 {
  65                compatible = "nvidia,tegra20-pwm";
  66                reg = <0x7000a000 0x100>;
  67                #pwm-cells = <2>;
  68        };
  69