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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>
This commit is contained in:
Thierry Reding 2014-04-07 15:45:30 +02:00
parent c9eaa447e7
commit 3e5314d3c8
1 changed files with 7 additions and 0 deletions
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7
Documentation/pwm.txt
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@ -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.
Locking
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