pwm: Document signal polarity convention

[linux-2.6-block.git] / Documentation / pwm.txt

diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 93cb979749860f323bb797ce2adc2923d629e1ed..0527f615b115cb38ff5bb314dd01f1e7709493f3 100644 (file)
--- 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.
+
 Locking
 -------