On 6/11/25 14:13, Mark Kettenis wrote:
From: Casey Connolly <casey.conno...@linaro.org>
Date: Tue, 10 Jun 2025 18:23:33 +0200
Hi Casey,
Since we're using the upstream file structure, we know at build time
the path to each DTB that we build. These same paths are used relative
to some (maybe version specific) dtb directory on the boot partition
or ESP.
By recording this path at build time and embedding it into the
devicetree, we can set the fdtfile environment variable with 100%
certainty that it is correct.
Devicetree file names are already treated as stable kernel API upstream,
since they are used by OS loaders extensively.
But when something similar was suggested some time ago, the Linux
kernel folks explicitly stated that the file names are ~*not*
considered to be ABI.
They don't /want/ it to be ABI, but that ship has long since sailed as
the filename is how the dtb is loaded. If this wasn't meant to be the
case then "make dtbs_install" should mangle filenames somehow.
So I think this proposal should be discussed in a broader context,
probably on the devicetree-s...@vger.kernel.org mailing list.
One could argue that since this property is added by the U-Boot build
system during compilation, and only expected to be consumed by U-Boot
itself, is could fall outside the purview here. But yeah... probably
.
Embedding the path into the devicetree itself just simplifies the
process and allows U-Boot or the OS loader to select a devicetree of a
different version for the specific board that U-Boot is running on.
Signed-off-by: Casey Connolly <casey.conno...@linaro.org>
---
scripts/Makefile.lib | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index
e89a4a51b74ddccfd9f0a6463cdeded12eaa5235..1f95bda0597c14d2ee785eb8058d607a6c819a56
100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -360,16 +360,31 @@ $(obj)/%.dtbo.S: $(obj)/%.dtbo
ifeq ($(CONFIG_OF_LIBFDT_OVERLAY),y)
DTC_FLAGS += -@
endif
+ifeq ($(CONFIG_ARM64),y)
+dt_dir := dts/upstream/src/arm64
+else
+dt_dir := dts/upstream/src/$(ARCH)
+endif
+
+ifeq ($(CONFIG_OF_UPSTREAM),y)
+# Embed the upstream path to the DTB into it as /chosen/fdtfile. This property
is used
+# at runtime to set the fdtfile variable
+dt_extra_snippet = / { chosen { fdtfile = "$(subst $(dt_dir)/,,$@)"; }; };
+else
+dt_extra_snippet =
+endif
+
quiet_cmd_dtc = DTC $@
# Modified for U-Boot
# Bring in any U-Boot-specific include at the end of the file
# And finally any custom .dtsi fragments specified with
CONFIG_DEVICE_TREE_INCLUDES
cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
(cat $< > $(pre-tmp)); \
$(foreach f,$(subst $(quote),,$(dtsi_include_list)
$(CONFIG_DEVICE_TREE_INCLUDES)), \
echo '$(pound)include "$(f)"' >> $(pre-tmp);) \
+ [[ -z "$(dt_extra_snippet)" ]] || echo '$(dt_extra_snippet)' >>
$(pre-tmp); \
$(HOSTCC) -E $(dtc_cpp_flags) -I$(obj) -x assembler-with-cpp -o
$(dtc-tmp) $(pre-tmp) ; \
$(DTC) -O dtb -o $@ -b 0 \
-i $(dir $<) -i $(u_boot_dtsi_loc) $(DTC_FLAGS) \
-d $(depfile).dtc.tmp $(dtc-tmp) || \
--
2.49.0
--
Casey (she/they)
