[U-Boot-Users] DTB /OF_TREE Newbie and U-boot

[U-Boot-Users] DTB /OF_TREE Newbie and U-boot

[Russell McGuire]

All,

 

Now that I have u-boot up and running on my MPC8360E I am going to begin
trying to boot Linux 2.6.15 or newer.

However, I keep seeing mention of these Device Tree Blobs and OF_TREE's
throughout the code.

 

I realize now that for SOC chips such as a MPC8360E that passing a DTB
structure into the bootm command is probably a required step??? Is this
True?

 

If so I see in some cases that this structure might be partly constructed
within the U-boot code, at least I see code doing something with OF_TREE's.

 

1)       Is the U-boot compilation process generating a .dtb structure that
we can burn into firmware, at least or certain CPU architectures?

2)       Is this a manual process that requires an outside dtb compiler, and
if so why is U-boot code dealing with this?

3)       Is this built into the bd_info structure?

 

Or I guess if somebody just has a documentation link I can just read, I
didn't see anything about OF_TREE's in the DULG manual.

 

Thanks,

 

-Russ

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[U-Boot-Users] DTB /OF_TREE Newbie and U-boot

[Timur Tabi]

Russell McGuire wrote:

> I realize now that for SOC chips such as a MPC8360E that passing a DTB 
> structure into the bootm command is probably a required step??? Is this 
> True?

Yes.

> If so I see in some cases that this structure might be partly 
> constructed within the U-boot code, at least I see code doing something 
> with OF_TREE?s.

Yes, U-Boot updates the tree with its own values.

> 1)       Is the U-boot compilation process generating a .dtb structure 
> that we can burn into firmware, at least or certain CPU architectures?

No.  You need to use the DTC compiler, which is available here: 
http://www.jdl.com/git_repos/?p=dtc.git

> 2)       Is this a manual process that requires an outside dtb compiler, 

Yes.

> and if so why is U-boot code dealing with this?

Because the Linux kernel is currently coded such that the boot loader must pass 
the DTB to it.  To reduce the amount of dual-maintenance, U-Boot can take some 
of the data that it knows about, and put that into the tree.

> 3)       Is this built into the bd_info structure?

I'm not sure I understand.  The DTB itself is not part of U-Boot, but U-Boot can 
parse the tree and modify it.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

[U-Boot-Users] DTB /OF_TREE Newbie and U-boot

[Jerry Van Baren]

Timur Tabi wrote:
> Russell McGuire wrote:

[snip]

>> 3)       Is this built into the bd_info structure?
> 
> I'm not sure I understand.  The DTB itself is not part of U-Boot, but U-Boot can 
> parse the tree and modify it.

The dtb obsoletes the bd_info structure (but that is directly or 
indirectly the source of some of the added information that bootm puts 
into the dtb).  Instead of passing a pointer to a C struct that is 
defined both in u-boot and the kernel (which must be identical or 
literally nothing happens), the dtb is structured as a searchable 
key/value data structure that is well defined.  If the necessary 
key/value is in there, it will be found an used.  If not, that will be 
reported if possible (some errors, e.g. bad console port definitions, 
are obviously not recoverable).

HTH,
gvb