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 (defined in 47<dt-bindings/pwm/pwm.h>) in a third cell: 48- PWM_POLARITY_INVERTED: invert the PWM signal polarity 49 50Example with optional PWM specifier for inverse polarity 51 52 bl: backlight { 53 pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED>; 54 pwm-names = "backlight"; 55 }; 56 572) PWM controller nodes 58----------------------- 59 60PWM controller nodes must specify the number of cells used for the 61specifier using the '#pwm-cells' property. 62 63An example PWM controller might look like this: 64 65 pwm: pwm@7000a000 { 66 compatible = "nvidia,tegra20-pwm"; 67 reg = <0x7000a000 0x100>; 68 #pwm-cells = <2>; 69 }; 70