followup: kernel manipulation of {bus,brg}-frequency for MPC8360?

Robert P. J. Day rpjday at
Sat May 7 23:09:31 AEST 2016

  followup to earlier post and WARNING -- my ppc dev box is suddenly
off the net so i'm doing all this from memory. le *sigh*.

  again in context of porting linux (4.1 kernel, using v2015.10 uboot)
to MPC8360 target, a couple of questions.

  first, while in this case u-boot might be modifying some of the
values in the DTB before passing it to the kernel, is it true that the
contents of the /proc/devicetree directory on the running linux system
represent the DTB as it was passed from u-boot, or after it was
possibly modified by the PPC kernel boot code? (clearly, this isn't
exclusively a PPC issue -- it's a more general device tree issue.)

  second (and more involved) question, i noticed pretty quickly that
the two frequency values i was interested in were visible under /sys
... from memory, /sys/firmware(?).../ and so on. i also noticed they
were stored in internal format so i needed to run them through
"hexdump" to get their values, no problem.

  i'm assuming *those* values for {bus,brg}-frequency visible under
/sys *are* the final values, after possible processing by the kernel
boot code. in my case (MPC8360), which ppc boot files are responsible
for checking the values passed in the DTB and possibly adjusting them
early in the boot process?

  not looking for extensive explanation, i already see what look like
potentially relevant files under arch/powerpc:

  * sysdev/fsl_soc.c
  * sysdev/qe_lib/qe.c
  * boot/devtree.c

am i at least looking in the right place? thanks.


p.s. if there is something online that addresses the values of
bus-frequency and brg-frequency that's relevant, by all means, let me
know. i'm just perusing the kernel doc file


Robert P. J. Day                                 Ottawa, Ontario, CANADA


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