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The PWM in Ingenic SoCs starts in inactive state until the internal timer reaches the duty value, then becomes active until the timer reaches the period value. In theory, we should then use (period - duty) as the real duty value, as a high duty value would otherwise result in the PWM pin being inactive most of the time. This is the reason why the duty value was inverted in the driver until now, but it still had the problem that it would not start with the active part. To address this remaining issue, the common trick is to invert the duty, and invert the polarity when the PWM is enabled. Since the duty was already inverted, and we invert it again, we now program the hardware for the requested duty, and simply invert the polarity when the PWM is enabled. Signed-off-by: Paul Cercueil <paul@crapouillou.net> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.