PL (programmable logic) uses FCLK0..FCLK3 as a clock sources.
Normally they're configured by first stage boot loader (FSBL)
and normal user never has to touch them. These sysctls may come
useful for hardware developers
hw.fpga.fclk.N.source: clock source (IO, DDR, ARM)
hw.fpga.fclk.N.freq: requested frequency in Hz
hw.fpga.fclk.N.actual_freq: actual frequency in Hz (R/O)
hw.fgpa.level_shifters: 0/1 to enable/disable PS-PL level shifters,
normally they're enabled either by FSBL or after programming
FPGA through devcfg(4)
to check the status property in their probe routines.
Simplebus used to only instantiate its children whose status="okay"
but that was improper behavior, fixed in r261352. Now that it doesn't
check anymore and probes all its children; the children all have to
do the check because really only the children know how to properly
interpret their status property strings.
Right now all existing drivers only understand "okay" versus something-
that's-not-okay, so they all use the new ofw_bus_status_okay() helper.
Communication on src-commiters, Sat, 27 Apr 2013 22:09:06 -0700,
Subject was: "Re: svn commit: r249997"
As I'm here, fix the style main block comments in files' headers.
