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 ::= [pwm-list] single-pwm ::= 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 ) 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>; };