[U-Boot] [PATCH v3 00/12] cmd: fdt: Add device tree overlays support

Maxime Ripard maxime.ripard at free-electrons.com
Fri Jun 24 16:27:45 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 it is currently a use-case.

There's still a bunch of work to extend the libfdt unit tests to test
the new functions introduced, but these patches will be submitted
in a near future.

Let me know what you think,

Changes from v2:
  - Add Kconfig option for the libfdt overlay support
  - Reworked the code to deal with Pantelis and David numerous
    comments, among which:
    * Remove the need for malloc in the overlay code, and added some
      libfdt functions to do that
    * Remove the DT magic in case of an error to not be able to use it
    * Removed the fdt_ and _ function prefix for the static functions
    * Plus the usual bunch of rework, error checking and optimizations.

  - Added new tests to deal with bugs reported by David (the overlay
    was not applying when you add a subnode declared that was already
    in the base device tree, and using a local phandle was only
    working if the property storing it only had a length of 4).

Changes from v1:
  - Moved the overlay code to libfdt
  - Added unit tests
  - Refactored the code to reduce the amount of memory allocation
  - No longer modify the overlay itself, but create a copy to operate
    on instead.
  - Removed the limitations on the fixups path, names and properties
  - Fixed a few things here and there according to comments		    

Maxime Ripard (12):
  cmd: fdt: Narrow the check for fdt addr
  scripts: Makefile.lib: Sanitize DTB names
  vsprintf: Include stdarg for va_list
  libfdt: Add new headers and defines
  libfdt: Add iterator over properties
  libfdt: Add max phandle retrieval function
  libfdt: Add fdt_setprop_inplace_by_index
  libfdt: Add fdt_path_offset_namelen
  libfdt: Add fdt_getprop_namelen_w
  libfdt: Add overlay application function
  cmd: fdt: add fdt overlay application subcommand
  tests: Introduce DT overlay tests

 Makefile                          |   1 +
 cmd/fdt.c                         |  26 ++-
 include/libfdt.h                  | 124 ++++++++++++-
 include/libfdt_env.h              |   6 +
 include/test/overlay.h            |  16 ++
 include/test/suites.h             |   1 +
 include/vsprintf.h                |   2 +
 lib/Kconfig                       |   5 +
 lib/libfdt/Makefile               |   2 +
 lib/libfdt/fdt_overlay.c          | 381 ++++++++++++++++++++++++++++++++++++++
 lib/libfdt/fdt_ro.c               |  44 ++++-
 lib/libfdt/fdt_wip.c              |  13 +-
 scripts/Makefile.lib              |   8 +-
 test/Kconfig                      |   1 +
 test/cmd_ut.c                     |   6 +
 test/overlay/Kconfig              |  11 ++
 test/overlay/Makefile             |  15 ++
 test/overlay/cmd_ut_overlay.c     | 243 ++++++++++++++++++++++++
 test/overlay/test-fdt-base.dts    |  21 +++
 test/overlay/test-fdt-overlay.dts |  88 +++++++++
 20 files changed, 992 insertions(+), 22 deletions(-)
 create mode 100644 include/test/overlay.h
 create mode 100644 lib/libfdt/fdt_overlay.c
 create mode 100644 test/overlay/Kconfig
 create mode 100644 test/overlay/Makefile
 create mode 100644 test/overlay/cmd_ut_overlay.c
 create mode 100644 test/overlay/test-fdt-base.dts
 create mode 100644 test/overlay/test-fdt-overlay.dts


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