On Thu, 16 Jun 2011, David Gibson wrote:

On Wed, Jun 15, 2011 at 03:50:37PM -0400, Nicolas Pitre wrote:

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On Tue, 14 Jun 2011, David Brown wrote:

quoted

Some targets have multiple memory regions.  Parse up to 8 of these
when converting the atags to fdt.

Signed-off-by: David Brown <redacted>

I've added your patch to my zImage patch queue.

quoted

With this change, I am able to boot MSM8x60 combining ATAGS and my DT.
It seems to work as long as my device tree has placeholders for all of
the properties I need.

I think those missing nodes should simply be created if missing.  I 
however don't see any function in the libfdt API to do that -- there is 
fdt_add_subnode() but no fdt_add_node().  Any DT expert please?

fdt_add_subnode() will create a new node as you require.  The
"subnode" is just supposed to indicate that the parameters are in the
form of the offset of the parent node and the new node's immediate
name, rather than taking a full path name for the new node.

Sure... but I'm still a total nincompoop with regard to FDT.

Let's suppose I do:

	offset = fdt_path_offset(fdt, "/memory");

but that returns -FDT_ERR_NOTFOUND.  Now what?

If I look at the documentation for fdt_add_subnode():

/**
 * fdt_add_subnode - creates a new node
 * @fdt: pointer to the device tree blob
 * @parentoffset: structure block offset of a node
 * @name: name of the subnode to locate
 * [...]

I have no node offset, and can't find the offset for the parent of an 
nonexistent node.  Should I use 0 for parentoffset here?  I'm guessing 
that "/memory" is at the top level so there is just no parent.

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Also, should the DTB be enlarged in order to add new nodes, or even 
modify existing ones with larger properties?  In other words, 
should something like fdt_move(fdt, fdt, fdt_totalsize(fdt)+HEADROOM) be 
used beforehand?

Yes, you will need to do this, fdt_open_into() is the function you
want.  Without making room first, adding nodes or expanding existing
properties will return -FDT_ERR_NOSPACE.  Once you've made whatever
edits you need, you can use fdt_pack() to collapse the tree back to
its minimum size.

Excellent!

FRom a quick code inspection, fdt_open_into() appears to be fine with 
both the source and destination pointers being the same, right?

Although this is somewhat awkward, this approach is a deliberate
design decision, to avoid making libfdt dependent on a working general
purpose allocator, which may not be available when libfdt is used in
very limited environments such as a firmware/bootloader.

This is perfect.  The environment where I want to use this code is 
fairly limited indeed.


Nicolas