PPC to PowerPC Migration

vb vb at vsbe.com
Wed Jun 11 23:55:32 EST 2008

I recently ported two platforms (8245 and 8541) from ppc tree in
earlier 2.6 versions into powerpc tree in 2.6.25. It is amazing how
little the device tree contents are described, a lot of things
required reverse engineering of the kernel code to understand the
meaning of some numbers in the  tree.

I am also willing to contribute into a document describing this
transition, please keep me in the loop,


On Tue, Jun 10, 2008 at 6:19 PM, Mike Timmons <mike_timmons at trimble.com> wrote:
> Great Idea Andrew. I am no long-serving expert, but over the past few
> years I've had some ARM-linux and more recently mpc5200 Linux exposure.
> For the mpc5200 we started as ppc under 2.6.16 a few months ago. I
> recently migrated to 2.6.24 with ARCH=powerpc.
> These were the conceptual difficulties I had at first:
> 1) Where the *%$# are the register address defines?
>        -Ahhh, the register definition header file maps to HW via the
> device tree. Cool. Now how the $%# do I interface to the tree from my
> drivers?
> 3) How do I request an IRQ?
>  You need to create a "device" in the device tree. This is
> non-intuitive because most of what you see in the tree when you start
> represents actual, "devices": SOC peripherals and such. I looked and
> looked for how to request
> IRQ3. It was so easy when I created a, "device" and specified the
> interrupt according to instructions in
> Documentation/powerpc/mpc5200xx-device-tree-bindings.txt.txt
> 4) How do I traverse the device tree from my code: my device drivers?
>  -functions like mpc52xx_find_and_map("name_from_dev_tree") are used to
> map peripheral registers to the relevant defined struct from your
> register definition header file.
>  - Also look for, "open firmware" (of) functions like
> irq_of_parse_and_map(node,0).
> - basically, the "find_and_map", and "parse_and_map" means your driver
> is traversing the device tree data. Grep on this sort of thing to find
> examples
> Of how various drivers interface to the device tree info.
> This is all very simple for so many of you, but I did wrestle with some
> conceptual difficulties. Andrew, if this makes any sense to you perhaps
> you
> Can roll it into your HOWTO. Perhaps we can collaborate offline and
> publish something more useful than what I just wrote above.
> -Mike
> -----Original Message-----
> From: linuxppc-embedded-bounces+mike_timmons=trimble.com at ozlabs.org
> [mailto:linuxppc-embedded-bounces+mike_timmons=trimble.com at ozlabs.org]
> On Behalf Of Andy Schmidt
> Sent: Tuesday, June 10, 2008 12:49 PM
> To: linuxppc-embedded at ozlabs.org
> Subject: PPC to PowerPC Migration
> I am wondering if anyone has seen any good documentation for migrating
> from the arch/ppc to arch/powerpc.  Specifically, I am working with a
> Xilinx board so I am more accustom to the xparamters.h vs. device
> trees.  I am very willing to build a (or multiple) tutorials to help
> others in my situation, I just need some initial help getting started.
>  If anyone can point me in the right direction, I will be sure to keep
> the group (or those interested) updated on the documentation.
> Thank you,
> Andrew
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