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, once things settle down.
Let me know what you think, Maxime
Changes from v3: - Moved the patch to introduce fdt_getprop_namelen_w earlier to keep bisectability - Renamed fdt_setprop_inplace_namelen_by_index in fdt_setprop_inplace_namelen_partial - Reintroduced the check on the property length in fdt_setprop_inplace - Made sure the code was taking the non 32bits-aligned phandles - Used memchr instead of strchr in the fixup parsing code, and made sure the cases where the fixup format was wrong was reported as an error. - Fixed a bug where a property in a overlay having multiple phandles local to that overlay would only resolve the first one. Also added a test case for this - Added kerneldocs for all the overlay functions - Added a patch to fix a typo in separator - A few fixes, function renamings, error checking changes here and there
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 (13): 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: Fix separator spelling libfdt: Add fdt_path_offset_namelen libfdt: Add fdt_getprop_namelen_w libfdt: Add fdt_setprop_inplace_namelen_partial 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 | 111 ++++++- 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 | 618 ++++++++++++++++++++++++++++++++++++++ lib/libfdt/fdt_ro.c | 46 ++- lib/libfdt/fdt_wip.c | 29 +- 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 | 268 +++++++++++++++++ test/overlay/test-fdt-base.dts | 21 ++ test/overlay/test-fdt-overlay.dts | 96 ++++++ 20 files changed, 1270 insertions(+), 19 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