projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 7299ab70 TR |
1 | Specifying PWM information for devices |
| 2 | ====================================== | |
| 3 | ||
| 4 | 1) PWM user nodes | |
| 5 | ----------------- | |
| 6 | ||
| 7 | PWM users should specify a list of PWM devices that they want to use | |
| 8 | with 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 | ||
| 16 | PWM properties should be named "pwms". The exact meaning of each pwms | |
| 17 | property must be documented in the device tree binding for each device. | |
| 18 | An optional property "pwm-names" may contain a list of strings to label | |
| 19 | each of the PWM devices listed in the "pwms" property. If no "pwm-names" | |
| 20 | property is given, the name of the user node will be used as fallback. | |
| 21 | ||
| 22 | Drivers 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 | |
| 24 | pwm_get() call to an index into the list given by the "pwms" property. | |
| 25 | ||
| 26 | The following example could be used to describe a PWM-based backlight | |
| 27 | device: | |
| 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 | ||
| 83af2402 PA |
40 | Note that in the example above, specifying the "pwm-names" is redundant |
| 41 | because the name "backlight" would be used as fallback anyway. | |
| 42 | ||
| 7299ab70 | 43 | pwm-specifier typically encodes the chip-relative PWM number and the PWM |
| 83af2402 PA |
44 | period in nanoseconds. |
| 45 | ||
| 9344dade LP |
46 | Optionally, 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 | |
| 83af2402 PA |
49 | |
| 50 | Example with optional PWM specifier for inverse polarity | |
| 51 | ||
| 52 | bl: backlight { | |
| 9344dade | 53 | pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED>; |
| 83af2402 PA |
54 | pwm-names = "backlight"; |
| 55 | }; | |
| 7299ab70 TR |
56 | |
| 57 | 2) PWM controller nodes | |
| 58 | ----------------------- | |
| 59 | ||
| 60 | PWM controller nodes must specify the number of cells used for the | |
| 61 | specifier using the '#pwm-cells' property. | |
| 62 | ||
| 63 | An 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 | }; |