community/linux-edge/APKBUILD : built dtbs with symbols to support dtb overlays
changes:
change make
to make DTC_FLAGS="-@"
on line 117
why:
TL,DR: load customized dtb modifications on top of original dtb without rebuilding/patching the kernel
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"-@" is from command dtc :
-@, --symbols : Enable generation of symbols
-
Linux kernel uses command dtc to generate dtbs (aka device tree blobs)
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with symbols enabled, it is possible to add modifications on top of original dtb via
u-boot extlinux.conf
without rebuilding/patching the kernel. :fdt /dtbs/original.dtb # needs to build with dtc -@ option fdtoverlays /my_first_custom_overlays.dtb /my_second_custom_overlays.dtb ... # needs to build with dtc -@ option
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the footprint is very small. it adds around 10KB size to each dtb generated. in my case, with
-@
enabled, the generated dtb size went from 30KB to 40KB for a full device tree blob. -
it is also possible to use
fdtoverlay -i original.dtb -o final.dtb my_custom_overlays.dtb
command to apply changes to original dtb and load the final dtb via u-boot extlinux.conffdt /final.dtb
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without -@ , none of above methods works, one has to download the whole kernel tree to apply changes and rebuild the dtb or send PR to kernel tree, which, is very complicated.