From 3e5314d3c8364b3e3611256caa005bb34e05372e Mon Sep 17 00:00:00 2001 From: Thierry Reding Date: Mon, 7 Apr 2014 15:45:30 +0200 Subject: 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 --- Documentation/pwm.txt | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'Documentation/pwm.txt') diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index 93cb97974986..0527f615b115 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. + Locking ------- -- cgit v1.2.3-59-g8ed1b