[Buildroot] [Help] Problem with BR2_LINUX_KERNEL_CUSTOM_DTS_PATH and kernel 6.12

* [Buildroot] [Help] Problem with BR2_LINUX_KERNEL_CUSTOM_DTS_PATH and kernel 6.12
@ 2025-01-01 12:59 Kilian Zinnecker via buildroot
  2025-01-01 13:13 ` Baruch Siach via buildroot
  0 siblings, 1 reply; 5+ messages in thread
From: Kilian Zinnecker via buildroot @ 2025-01-01 12:59 UTC (permalink / raw)
  To: buildroot

Hello all,

I am struggeling to get a custom device tree compiled as part of a developing 
a board support (i.e., for the beaglev-ahead). And I suspect it might have to 
do with a recent change to mainline kernel 6.12, which buildroot might not 
take into account yet. Here is what I try:

I add my own device tree source file into the board folder and set the 
following lines in my defconfig:

BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_VERSION=y
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.12.7"
BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
BR2_LINUX_KERNEL_DTS_SUPPORT=y
# BR2_LINUX_KERNEL_INTREE_DTS_NAME is not set
BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/beaglev-ahead/beaglev-ahead.dts"
BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT=y

Now when the kernel gets build, the Makefile throws the error, that there 
exists no rule to build my particular dtb. I checked, an my custom dts file 
actually gets copied into arch/riscv/boot/dts. Also in this folder, there is a 
"dtbs-list" text file, which is not part of the original kernel tree, but seems 
to get created during some configuration step. This file lists a lot of dtb file 
paths, but there is none for my particular custom device tree. So I grepped to 
identfy where this file gets created and it seems that it was introduced into 
scripts/Makefile.dtbs in this commit, which is from September 2024:

https://github.com/torvalds/linux/commit/
e7e2941300d258d551dda6ca9a370e29e085fa73

Using "git tag --contains e7e2941300d25" shows, that the commit is part of 
kernel version 6.12.

I don't fully understand the mechanisms yet (i.e., how kernel 6.12.7 decides 
which dtbs can be built), but I suspect, that maybe now the kernel creates 
such list, which is somehow used to derive the Makefile targets for the dtbs 
(i.e., which dtbs can actually be build). And I also suspect, that maybe 
buildroot does not take this into accout yet and therefore my custom dtb does 
not appear in that list, and hence does not get build. ... Or I overlook some 
mistake on my side and am doing something wrong here, which causes the error.

Could anybody have a look and help me out with this issue?

Thanks and best regards,
Kilian

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