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Re: [RFC PATCH 06/10] MIPS: Octeon: Initialize and fixup device tree.

To: Grant Likely <grant.likely@secretlab.ca>
Subject: Re: [RFC PATCH 06/10] MIPS: Octeon: Initialize and fixup device tree.
From: David Daney <ddaney@caviumnetworks.com>
Date: Wed, 23 Feb 2011 11:20:09 -0800
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org, devicetree-discuss@lists.ozlabs.org, linux-kernel@vger.kernel.org
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On 02/23/2011 10:51 AM, Grant Likely wrote:
On Wed, Feb 23, 2011 at 10:40:32AM -0800, David Daney wrote:
On 02/23/2011 09:41 AM, Grant Likely wrote:
On Tue, Feb 22, 2011 at 12:57:50PM -0800, David Daney wrote:
Signed-off-by: David Daney<ddaney@caviumnetworks.com>
---
  arch/mips/Kconfig                         |    2 +
  arch/mips/cavium-octeon/octeon-platform.c |  280 +++++++++++++++++++++++++++++
  arch/mips/cavium-octeon/setup.c           |   17 ++
  3 files changed, 299 insertions(+), 0 deletions(-)

I've got an odd feeling of foreboding about this patch.  It makes me
nervous, but I can't articulate why yet.  Gut-wise I'd rather see the
device tree pruned/fixed up before it gets unflattened,

I chose to work on the unflattened form because there were already
functions to do it.  I didn't see anything that would make
manipulating the flattened form easy.

I agree that working on the unflattened form would be best.  At a
minium the /proc/device-tree structure would better reflect reality.

What do you think about adding some helper functions to
drivers/of/fdt.c for the manipulation of the flattened form?

It would probably be easier/safer to link libfdt into the kernel
proper.  It's already used in the powerpc bootwrapper, and there has
been talk about replacing some of fdt.c with libfdt.  See
scripts/dtc/libfdt


I will take a look at that approach.


or for the
kernel to have a separate .dtb linked in for each legacy platform.

I think there are too many variants to make this viable.

Out of curiosity, how many variants?


I don't know exactly, but for the sake of argument let's say at least twenty we support in-house. That is not counting close to 100 customer boards. Some of these boards have modular I/O connections (SPI-4.2 vs. XAIU vs. 4xSGMII, etc. across several different ports.), so the hardware configuration may be different each time they are powered on.

The existing legacy code handles these, so using it to configure the Device Tree has a certain appeal. I would hope that moving forward a correct device tree is obtained from the bootloader, but for existing boards...

btw, did you know about the dtc '/include/' functionality?  It is
possible to set up .dts include files that represent a SoC and can be
modified by the .dts files that include them.  See
arch/powerpc/boot/dts/*5200*.dts

Yes.

Thanks,
David Daney

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