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authorThierry Reding <thierry.reding@gmail.com>2014-04-07 15:45:30 +0200
committerThierry Reding <thierry.reding@gmail.com>2014-04-28 13:04:59 +0200
commit3e5314d3c8364b3e3611256caa005bb34e05372e (patch)
treeee7cf0715d4c6053f3f66280ff8a60038b05a3b5 /Documentation/pwm.txt
parentc9eaa447e77efe77b7fa4c953bd62de8297fd6c5 (diff)
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pwm: Document signal polarity convention
The PWM subsystem defines normal and inversed PWM signal polarity in an unambiguous way. In addition to the documentation in the linux/pwm.h header file, add a paragraph in Documentation/pwm.txt because people are likely to look there for guidance. Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'Documentation/pwm.txt')
-rw-r--r--Documentation/pwm.txt7
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diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 93cb979..0527f61 100644
--- a/Documentation/pwm.txt
+++ b/Documentation/pwm.txt
@@ -97,6 +97,13 @@ pwm_chip as argument which provides a description of the PWM chip, the
number of PWM devices provided by the chip and the chip-specific
implementation of the supported PWM operations to the framework.
+When implementing polarity support in a PWM driver, make sure to respect the
+signal conventions in the PWM framework. By definition, normal polarity
+characterizes a signal starts high for the duration of the duty cycle and
+goes low for the remainder of the period. Conversely, a signal with inversed
+polarity starts low for the duration of the duty cycle and goes high for the
+remainder of the period.
+
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