Re: [PATCH v3 00/12] cmd: fdt: Add device tree overlays support

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Fri, Jun 24, 2016 at 04:27:45PM +0200, Maxime Ripard wrote:
> Hi,
> 
> 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
> running.
> 
> 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.

Are you planning to send a new version of (the relevant portions of)
these against upstream libfdt?

> 
> Let me know what you think,
> Maxime
> 
> 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
>       anymore
>     * 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
>     length
>   - 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
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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