Flat OF Device Tree for ppc32 [was: Platform bus/ppc sys model...]

Andrei Konovalov akonovalov at ru.mvista.com
Mon Apr 4 20:56:21 EST 2005

Hi Jakob!

Yes, Jon Loeliger's implementation plan looks OK for me
(as far as I understood Jon's posting; having look at
the current patch would be great). And I could participate
in the implementation for Xilinx if needed too, but don't
object if you do it by yourself (at the moment, I know
little about the OF device tree, so just testing the patch
on ML300 would be fine for me as well).

Should we rely on U-Boot to give that device tree structure to
the kernel? If I got it correct this is how the Freescale team
plans to proceed. Jon (Masters), are you going the same way?
Anyone using arch/ppc/boot/simple bootwrapper with his Virtex 2 Pro
board? If we drop Virtex 2 Pro support in arch/ppc/boot and move to
U-Boot would it hurt anyone?


Jakob Viketoft wrote:
> Hi!
> You don't happen to have a patch of your current work against one of the 
> trees (83xx and 85xx)? It would be much easier to do work in parallell, 
> and I'd be happy to do it on the "Xilinx" tree (and help out where I 
> can, of course).
> Jon Masters and Andrei: Does Jon Loeliger's implementation plan sound 
> alright to you? Since you seem quite full-handed on your end anyway, 
> Jon, I'll be happy to do the work needed unless anyone has any 
> objections...
> Cheers!
>     /Jakob
> Jon Loeliger wrote:
>> On Thu, 2005-03-31 at 06:33, Jon Masters wrote:
>>> Kumar Gala wrote:
>>> |> My intention was to give a device tree structure to the kernel at 
>>> boot
>>> |> time via a (pseudo?) pointer in bd_info or similar. 
>>> This got resurrected recently. 
>> Hi!
>>> | I think this is reasonable.  The best device tree would be a flattened
>>> | OF tree since we are trying to move the world in that direction.  Jon
>>> | Masters around?
>>> Yes, but I've been tied up with worky and magazine stuff again. If
>>> someone wants to work with me then this might actually happen.
>> Hi Jon,
>> I'm here and actively(!) working on it now.   Here is the very
>> rough plan as Kumar and I have discussed it.  Please feel free
>> to comment on it or offer suggestions.  Ben has suggested that
>> I start with the "second step" below.  I'd like to do a round
>> of cleanup first.
>> So far, I have taken the first step of isolating the references
>> to the global __res[] variable into one file and replacing all
>> references to the data in the bd_t structure with a thin, shim
>> layer of function calls that are nominally into an OF-like
>> interface.  I have done this for all the 85xx and 83xx boards
>> in my development tree, and am working on the others now.
>> This step effectively isolates the __res[] references to one
>> file where a well defined interface can be created to pose as
>> an OF Device Tree layer (briefly).
>> As a follow-up second step, I plan on introducing essentially
>> the same code currently in ppc64 to handle the flat device tree
>> and provide an interface to that data in exactly the same manner
>> as the ppc64 currently has.  I understand the desire to have the
>> flat-tree handling be "outside the kernel".
>> As a third step, the shim layer will be rewritten/augmented to
>> use the actual OF device tree data where it currently fronts
>> for the bd_t data.
>> Finally, as time permits and maintainers allow (read: prod),
>> the other (not 85xx, not 83xx) boards can have their setup code
>> converted to use the "real" OF device tree function calls.
>> When all of that is done, the shim layer can be removed, as needed.
>> Oh, yeah.  Um, also on my plate will be to construct the
>> original flat-tree blob in U-Boot to be handed to the kernel.
>> (I'll start with 85xx and 83xx, naturlich.)
>> We have not yet decided on the layout of that tree to determine
>> where all the attributes and devices really belong.  I will
>> also discuss with Wolfgang and crew how to generate that tree
>> over in U-Boot land.
>> Right?
>> Thanks,
>> jdl

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