0bc69592ab
In general, PLL has VCO (= Voltage controlled oscillator),
one of the very important electronic feature called as "jitter"
is related to this VCO.
In academic generalism, VCO should be maximum to be more small jitter.
In high frequency clock, jitter will be large impact.
Thus, selecting Hi VCO is general theory.
fin fvco fout fclkout
in --> [1/M] --> |PD| -> [LPF] -> [VCO] -> [1/P] -+-> [1/FDPLL] -> out
+-> | | |
| |
+-----------------[1/N]<-------------+
fclkout = fvco / P / FDPLL -- (1)
In PD, it will loop until fin/M = fvco/P/N
fvco = fin * P * N / M -- (2)
(1) + (2) indicates
fclkout = fin * N / M / FDPLL
In this device, N = (n + 1), M = (m + 1), P = 2, FDPLL = (fdpll + 1).
fclkout = fin * (n + 1) / (m + 1) / (fdpll + 1)
This is the datasheet formula.
One note here is that it should be 2kHz < fvco < 4096MHz
To be smaller jitter, fvco should be maximum,
in other words, N as large as possible, M as small as possible driver
should select. Here, basically M=1.
This patch do it.
Reported-by: HIROSHI INOSE <hiroshi.inose.rb@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[Small clarifications in comments, renamed finnm to fout]
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.