Bug#884003: FDT overlay support
Source: flash-kernel
Severity: wishlist
Recent u-boot versions support fdt overlays. It can load a base dtb,
apply various overlays to it, and pass the final device tree to the kernel.
To be able to use such overlays:
1) u-boot has to be compiled with CONFIG_OF_LIBFDT_OVERLAY
2) the base dtb has to be compiled with "-@" / "--symbols"
3) all overlays have to be compiled with "-@" / "--symbols"
1: already given for debian's u-boot for ti's beagle bone black, which
is what I tested this on
2: not the default for the kernel dtb files, I used [1] as a quick hack
3: this should just be the user's responsibility for now (until there's
a centralized repository or something debian could just package)
With the quick&dirty boot script [2] I can then successfully boot
debian's kernel with applied overlays of my choosing.
That's great, especially since it's way to painful to just enable basic
stuff like spi. Now we "just" need a way for flash-kernel to support it ;)
One way could be:
- overlays need to be in /boot/dtbs/overlays
- user sets a list of overlays in /etc/defaults/flash-kernel
like "OVERLAYS=am335x-bone-black-disable-video
am335x-bone-black-disable-audio am335x-bone-black-spidev0
am335x-bone-black-spidev1"
- flash-kernel passes the list of overlays to it's u-boot boot script
- the boot script loads and applies all requested overlays
[1]
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 04b5633df1cf..e339d40c02d1 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -308,7 +308,7 @@ $(obj)/%.dtb.S: $(obj)/%.dtb
quiet_cmd_dtc = DTC $@
cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
$(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
- $(DTC) -O dtb -o $@ -b 0 \
+ $(DTC) -@ -O dtb -o $@ -b 0 \
$(addprefix -i,$(dir $<) $(DTC_INCLUDE)) $(DTC_FLAGS) \
-d $(depfile).dtc.tmp $(dtc-tmp) ; \
cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
[2]
load mmc 1 $fdt_addr_r am335x-boneblack.dtb
fdt addr $fdt_addr_r
fdt resize 8192
load mmc 1 $ramdisk_addr_r am335x-bone-black-disable-video.dtb
fdt apply $ramdisk_addr_r
load mmc 1 $ramdisk_addr_r am335x-bone-black-disable-audio.dtb
fdt apply $ramdisk_addr_r
load mmc 1 $ramdisk_addr_r am335x-bone-black-spidev0.dtb
fdt apply $ramdisk_addr_r
load mmc 1 $ramdisk_addr_r am335x-bone-black-spidev1.dtb
fdt apply $ramdisk_addr_r
...
Reply to: