So, like, Chris Packham said:

Hi,

This probably should come via git://git.jdl.com/software/dtc.git however
this appears to be inaccessible at the moment. Is this still the
canonical source for the device tree compiler and libfdt or has it been
moved? How much deviation from the canonical source are we prepared to
live with in the kernel?

That is because the official DTC repository has moved to git.kernel.org!

Currently in arch and driver code that needs early access to the
flattened device tree it is necessary to add specific CFLAGS so that
when scripts/dtc/libfdt/libfdt.h is included the C preprocessor is able
to locate the libfdt versions of libfdt_env.h and fdt.h without
generating an error.

We already provide an alternative linux-specific
version of libfdt_env.h and directly include scripts/dtc/libfdt/fdt.h
so the inclusion by scripts/dtc/libfdt/libfdt.h is a no-op thanks to the
inclusion guards.

By using quotes in scripts/dtc/libfdt/libfdt.h it picks up fdt.h and
libfdt_env.h from the source directory without needing to add CFLAGS for
the sources that happen to include linux/libfdt.h.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
---

and:

Hmm.  I seem to recall that the use of angle brackets was intentional.
I believe that was predicated on installing the FDT library on some
target machine and needing it to be able to find the other header
files in an installation, not source, directory.

Minor repository spelunking suggests that the angle brackets have
been around since Day Zero:

    commit 3da0f9a10dfa9b615d06c350c7b9fe29f360a6e0

David?

HTH?,
jdl