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While mathematically it's ok to calculate the number of cyles for the duty cycle as: duty_cycles = period_cycles * duty_ns / period_ns this doesn't always give the right result when doing integer math. This is best demonstrated using an example: With the input clock running at 208877930 Hz a request for duty_cycle = 383 ns and period = 49996 ns results in period_cycles = clkrate * period_ns / NSEC_PER_SEC = 10443.06098828 Now calculating duty_cycles with the above formula gives: duty_cycles = 10443.06098828 * 383 / 49996 = 80.00024719 However with period_cycle truncated to an integer results in: duty_cycles = 10443 * 383 / 49996 = 79.99977998239859 So while a value of (a little more than) 80 would be the right result, only 79 is used here. The problem here is that 14443 is a rounded result that should better not be used to do further math. So to fix that use the exact formular similar to how period_cycles is calculated. Link: https://lore.kernel.org/r/7628ecd8a7538aa5a7397f0fc4199a077168e8a6.1710711976.git.u.kleine-koenig@pengutronix.de Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
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 reStructuredText 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.