On Thu, Aug 21, 2008 at 3:43 AM, David Jander [off-list ref] wrote:

On Thursday 21 August 2008 01:24:46 Laxmikant Rashinkar wrote:

quoted

Hi,

I have an embedded PowerPC (MPC8347) board that works fine with uboot and
Linux 2.6.15.

I am trying to upgrade the kernel so that it runs on the latest release -
Linux 2.6.27. So far, I have gotten the kernel to compile on my platform,
but of course it does not boot.

Well, honestly I don't know where to look for information either (other than
the source-code and examples from others), but here is a list with points to
look out for (I have just done the same thing as you for a MPC5200B-based
board):

1. Upgrade to latest u-boot first (recent git seems to be fine). There have
been a lot of changes in u-boot lately about OF and device-tree related
things. I suspect you need a fairly recent version of u-boot to go well with
the latest kernel. It's also generally a good idea IMHO.

You don't *have* to do this though.  There is a target called
'cuImage.<myboard>' which will embed the device tree blob in the
kernel image and is backwards compatible with older u-boot versions.
See arch/powerpc/boot/Makefile and arch/powerpc/boot/wrapper to see
how this is generated.

There is a new document that might help in Documentation/powerpc/bootwrapper.txt

2. I assume you are porting to arch/powerpc (the old arch/ppc you used back in
2.6.15 is obsolete and broken now).

Not just broken; completely removed!  :-)

3. Look at other platforms that use the same processor, and pick a simple one
as starting point. Look out for the dts (device-tree-source file in
arch/powerpc/boot/dts), copy and modify one to reflect your hardware.
Recently a lot of changes happend in the kernel, changing device names,
obsoleting "device-type" tags, etc..., so some of the current DTS sources
included in the kernel might not even work (wrong device name, missing
information, wrong use of "device-type", etc...), so watch out for these kind
of issues too.

The goal is *not* to break existing device trees because we do not
know what has been deployed already and it some cases it is not
feasible to update the device tree on a device.  So, even though
conventions have been refined and changed, backwards compatibility
with older trees is supposed to be preserved.

3b. Once you've written your device tree, post it to the
devicetree-discuss@ozlabs.org mailing list and ask for review.

4. Be sure that the device(s) necessary to produce output on your console are
correctly placed in the DT. Also make sure that u-boot knows about it
(#define OF_STDOUT_PATH... in your u-boot board config file)

5. When compiling the device tree, it may be necessary to add some extra
reserved entries to the compiled tree (I am using dtc -p 10240 -R 20, which
might be slightly exaggerated), because u-boot may add something to it, and
if it can't, linux won't boot.

6. Remember to always specify the "rootfstype=" option on the commandline if
booting from anything other than NFS. This was not necessary back in the
2.6.15-times AFAICR.

7. Boot with a device-tree (in u-boot: "bootm $addrofkernel - $addrofdtb",
don't forget the dash if you are not using an initrd). If you don't do this,
u-boot can't fix your DT, and the kernel probably won't find it either.

8. Be sure to use the correct version of the DTC (DT compiler) for your kernel
(the sources are included nowadays, somewhere in arch/powerpc/boot IIRC). The
command used to compile, should probably be something like this:

$ ./dtc -p 10240 -R 20 -I dts -o myplatform.dtb -O dtb -b 0 dts/myplatform.dts

There is a makefile target now to help you with this and pass the
right options for reserving entries:

$ make myplatform.dtb

The dtb image will appear in arch/powerpc/boot

Load the resulting .dtb file directly with u-boot (don't make an u-image out
of it).

That's all I remember right now... hope it helps.

Regards,

--
David Jander
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Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.