This series introduces a new devicetree property in /chosen named
"fdtfile". This string array contains the upstream relative path to the
devicetree (e.g. "qcom/qcs4690-rb3gen2.dtb") and may in the future also
list the overlays in use. It is set at build time for OF_UPSTREAM builds
where we know the correct path.
Then we read out this property at runtime and set the fdtfile variable
in U-Boots environment.
This provides a fully consistent way to set fdtfile so that U-Boot or
another OS Loader could find the correct devicetree file associated with
the kernel version being run, since it isn't always preferable to pass
to the devicetree from U-Boot.
Currently, U-Boot searches some subdirectories in the ESP for the
fdtfile when booting with EFI, and uses it when booting with extlinux.
However today with EFI booting it is impossible to find the DTB when
there are multiple kernel versions available, for this we need to
integrate with the OS loader.
In the future, the fdtfile variable should be exported as an EFI
variable which can be appended to a devicetree-directory property in the
OS loader configuration to find the correct devicetree for the kernel
version being booted.
This will allow users to safely roll back their kernel and devicetree
together if there is a bug in a new kernel release.
Ideally devicetree would be stable for all platforms and none of this
would be necessary, but this is unfortunately not yet the case. This
series attempts to make the best of this bad situation by providing the
safest possible user experience.
Feedback is welcome on how to implement the EFI variable part of this,
as I'm not sure where it belongs. I didn't want to hold the rest of the
series back since I'm sure it will be useful elsewhere.
---
Casey Connolly (3):
dts/upstream: write fdtfile path to /chosen/fdtfile
env: set fdtfile environment variable from /chosen/fdtfile
mach-snapdragon: skip setting fdtfile if already set
arch/arm/mach-snapdragon/board.c | 5 +++++
common/board_r.c | 35 +++++++++++++++++++++++++++++++++++
scripts/Makefile.lib | 15 +++++++++++++++
3 files changed, 55 insertions(+)
---
base-commit: 87e02cbb78a2897d43db0f732e926b73d9c0823e
change-id: 20250610-b4-fdtfile-from-dt-0bd7930ad62c
Casey Connolly <casey.conno...@linaro.org>
