Update this function's comment and also the livetree documentation, so it
is clear when to use the function.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a function to copy properties from one node to another.

Signed-off-by: Simon Glass <sjg@chromium.org>

At present ofnode_write_prop() is inconsistent between livetree and
flattree, in that livetree requires the caller to ensure the property
value is stable (e.g. in rodata or allocated) but flattree does not, since
it makes a copy.

This makes the API call a bit painful to use, since the caller must do
different things depending on OF_LIVE.

Add a new 'copy' argument which tells the function to make a copy if
needed. Add some tests to cover this behaviour.

Signed-off-by: Simon Glass <sjg@chromium.org>

Some ofnode functions can only operate on the default device tree, i.e.
U-Boot's control FDT. Add comments to that effect. Fix up the reference to
device tree bindings while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add the logic to redirect requests for the device tree through a function
which can look up the tree ID. This works by using the top bits of
ofnode.of_offset to encode a tree.

It is assumed that there will only be a few device trees used at runtime,
typically the control FDT (always tree ID 0) and possibly a separate FDT
to be passed the OS.

The maximum number of device trees supported at runtime is 8, with this
implementation. That would use bits 30:28 of the node-offset value,
meaning that the positive offset range is limited to bits 27:0, versus
30:1 with this feature disabled. That still allows a device tree of up
to 256MB, which should be enough for most FITs. Larger ones can be
supported by using external data with the FIT, or by enabling OF_LIVE.

Update the documentation a little and fix up the comment for
ofnode_valid().

Signed-off-by: Simon Glass <sjg@chromium.org>

This function turns out to be a little confusing since it looks up a path
and also registers the tree. Split it into two, one that gets the root
node and one that looks up a path, so the purpose is clear.

Registering the tree will happen in a function to be added in a later
patch, called oftree_from_fdt().

Signed-off-by: Simon Glass <sjg@chromium.org>

In some cases we want to obtain an ofnode in the same tree as a different
ofnode, such as when looking up a subnode. At present this is trivial,
since there is only one tree. When there are multiple trees, this
implementation will change.

Also move the ofnode_to_offset() function up higher in the header file,
since we will need to provide a different implementation with multiple
trees.

Signed-off-by: Simon Glass <sjg@chromium.org>

When we have multiple trees, the ofnode logic needs to be told which one
to use. Create a new function which takes an oftree argument, along with
a helper to obtain the FDT pointer from an oftree.

Signed-off-by: Simon Glass <sjg@chromium.org>

At present dm_test_ofnode_root() does this manually. Add some inline
functions to handle it, so this code can be centralised.

Add oftree functions to produce a null tree and to check whether a tree
is valid or not.

Signed-off-by: Simon Glass <sjg@chromium.org>

The flat device tree is assumed to be the control FDT but this is not
always the case. Update the ofnode implementation to obtain the node via
an function call so we can eventually add support for selecting different
trees.

Signed-off-by: Simon Glass <sjg@chromium.org>