Re: [RFC][PATCH 08/30] powerpc/85xx: Rework P1020 SoC device tree

On Nov 10, 2011, at 12:58 PM, Scott Wood wrote:

On Thu, Nov 10, 2011 at 12:46:27PM -0600, Kumar Gala wrote:

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On Nov 10, 2011, at 12:05 PM, Scott Wood wrote:
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On Thu, Nov 10, 2011 at 10:13:51AM -0600, Kumar Gala wrote:

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Split the P1020 SoC device tree into what we can include as a =

'prefix'

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to the board device tree and what needs to be included as a =

'postfix'.

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This allows use more re-use and less duplication between various =

board

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device tree configurations (32-bit address map vs 36-bit address =

map).

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Could you elaborate on the issues that require this pre/post =

approach?

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We utilize two 'features' of dtc to accomplish things.  One is =

includes the other is 'merging of labeled nodes'.

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We can using merging to allow the board to specify the "reg" & =

"ranges"

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values of a SoC node that might vary between physical address maps
(32-bit vs 36-bit as example).
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dtc is able to 'merge' multiple labeled nodes as well.  So we use =

that

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to handle board specific values for something like localbus if we =

want

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to support both a 32-bit and 36-bit address map.
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What does the SoC part need to specify that has to override or go =

within

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something the board specifies?

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Not sure I follow the question.

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My question is, why does the stuff in post need to be in post, versus =

pre?

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Why can't pre define the soc node, and let the board dts set ranges?=20=

Likewise for localbus, pci, etc.
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-Scott

Gotcha, the reason we have -pre and -post is because of how dtc include =
mechanism works.  It builds it's tree in the order things are parsed in =
the file.  In addition, "labeled nodes" like we have in post for 'soc', =
'lbc', etc. have to be defined after they are referenced.

- k=