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 is currently a use-case.
Let me know what you think, Maxime
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