mainlining shenanigans
35240ba26a
Current calculator doesn't do it' job quite correct. First of all the
max310x baud-rates generator supports the divisor being less than 16.
In this case the x2/x4 modes can be used to double or quadruple
the reference frequency. But the current baud-rate setter function
just filters all these modes out by the first condition and setups
these modes only if there is a clocks-baud division remainder. The former
doesn't seem right at all, since enabling the x2/x4 modes causes the line
noise tolerance reduction and should be only used as a last resort to
enable a requested too high baud-rate.
Finally the fraction is supposed to be calculated from D = Fref/(c*baud)
formulae, but not from D % 16, which causes the precision loss. So to speak
the current baud-rate calculator code works well only if the baud perfectly
fits to the uart reference input frequency.
Lets fix the calculator by implementing the algo fully compliant with
the fractional baud-rate generator described in the datasheet:
D = Fref / (c*baud), where c={16,8,4} is the x1/x2/x4 rate mode
respectively, Fref - reference input frequency. The divisor fraction is
calculated from the same formulae, but making sure it is found with a
resolution of 0.0625 (four bits).
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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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.