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Documentation / devicetree / bindings / pwm / pwm.txt




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Based on kernel version 3.9. Page generated on 2013-05-02 23:00 EST.

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 in a third cell:
47	- bit 0: PWM signal polarity (0: normal polarity, 1: inverse polarity)
48	
49	Example with optional PWM specifier for inverse polarity
50	
51		bl: backlight {
52			pwms = <&pwm 0 5000000 1>;
53			pwm-names = "backlight";
54		};
55	
56	2) PWM controller nodes
57	-----------------------
58	
59	PWM controller nodes must specify the number of cells used for the
60	specifier using the '#pwm-cells' property.
61	
62	An 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		};
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