[U-Boot] [PATCH 0/2] cmd: fdt: Add device tree overlays support

Maxime Ripard maxime.ripard at free-electrons.com
Sat Apr 2 23:06:12 CEST 2016


The device tree overlays are a great solution to the issue raised by
the bunch expandable boards we find everywhere these days, like the
Beaglebone, Raspberry Pi or CHIP.

However, most of the time, the overlays are applied through a
mechanism involving the firmware request interface in Linux, that is
only fully functional once the userspace has been mounted and is

Some expansion boards might need to be enabled before that, because
they simply need to patch the DT early on, or need to be initialized
early in order to be fully functional, or because they provide access
to the root filesystem.

In these cases, having the bootloader applying the overlay before
Linux starts seems like the easiest solution.

This implementation doesn't provide all the Linux fancyness though,
there's no transactional application, which means that if the overlay
cannot be applied for a reason while you're still halfway through the
application, you're probably screwed. It also cannot remove an
overlay, but I don't think that is currently a use-case.

Let me know what you think,

Maxime Ripard (2):
  cmd: fdt: Narrow the check for fdt addr
  cmd: fdt: add fdt overlay application subcommand

 cmd/Makefile          |   2 +-
 cmd/fdt.c             |  21 ++-
 cmd/fdt_overlay.c     | 464 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/fdt_support.h |   2 +-
 4 files changed, 486 insertions(+), 3 deletions(-)
 create mode 100644 cmd/fdt_overlay.c


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