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
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
43 pwm-specifier typically encodes the chip-relative PWM number and the PWM
44 period in nanoseconds.
45
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
49
50 Example 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
57 2) PWM controller nodes
58 -----------------------
59
60 See pwm.yaml.
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