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authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
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treeb9996006addfd7ae70a39672b76843b49aebc189 /Documentation/devicetree/bindings/pwm/pwm.txt
downloadlinux-linaro-highbank-3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a.tar.gz
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+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 ::= <single-pwm> [pwm-list]
+ single-pwm ::= <pwm-phandle> <pwm-specifier>
+ 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 in a third cell:
+- bit 0: PWM signal polarity (0: normal polarity, 1: inverse polarity)
+
+Example with optional PWM specifier for inverse polarity
+
+ bl: backlight {
+ pwms = <&pwm 0 5000000 1>;
+ 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>;
+ };