[U-Boot] [PATCH v3 2/6] fdt: Add support for embedded device tree (CONFIG_OF_EMBED)

[Simon Glass]

Hi Stephen,

On Thu, Oct 13, 2011 at 2:21 PM, Stephen Warren <swarren at nvidia.com> wrote:
> Simon Glass wrote at Tuesday, October 11, 2011 4:26 PM:
>> This new option allows U-Boot to embed a binary device tree into its image
>> to allow run-time control of peripherals. This device tree is for U-Boot's
>> own use and is not necessarily the same one as is passed to the kernel.
>>
>> The device tree compiler output should be placed in the $(obj)
>> rooted tree. Since $(OBJCOPY) insists on adding the path to the
>> generated symbol names, to ensure consistency it should be
>> invoked from the directory where the .dtb file is located and
>> given the input file name without the path.
> ...
>> +process_lds = \
>> +     $(1) | sed -r -n 's/^OUTPUT_$(2)[ ("]*([^")]*).*/\1/p'
>> +
>> +# Run the compiler and get the link script from the linker
>> +GET_LDS = $(CC) $(CFLAGS) $(LDFLAGS) -Wl,--verbose 2>&1
>> +
>> +$(obj)dt.o: $(DT_BIN)
>> +     # We want the output format and arch.
>> +     # We also hope to win a prize for ugliest Makefile / shell interaction
>> +     # We look in the LDSCRIPT first.
>> +     # Then try the linker which should give us the answer.
>> +     # Then check it worked.
>> +     oformat=`$(call process_lds,cat $(LDSCRIPT),FORMAT)` ;\
>> +     oarch=`$(call process_lds,cat $(LDSCRIPT),ARCH)` ;\
>> +     \
>> +     [ -z $${oformat} ] && \
>> +             oformat=`$(call process_lds,$(GET_LDS),FORMAT)` ;\
>> +     [ -z $${oarch} ] && \
>> +             oarch=`$(call process_lds,$(GET_LDS),ARCH)` ;\
>> +     \
>> +     [ -z $${oformat} ] && \
>> +             echo "Cannot read OUTPUT_FORMAT from lds file $(LDSCRIPT)" && \
>> +             exit 1 || true ;\
>> +     [ -z $${oarch} ] && \
>> +             echo "Cannot read OUTPUT_ARCH from lds file $(LDSCRIPT)" && \
>> +             exit 1 || true ;\
>> +     \
>> +     cd $(dir ${DT_BIN}) && \
>> +     $(OBJCOPY) -I binary -O $${oformat} -B $${oarch} \
>> +             $(notdir ${DT_BIN}) $@
>> +     rm $(DT_BIN)
>
> Instead of all that, can't you just run a trivial script to generate a .c
> file containing the data from DTB_BIN, and then use the compiler to compile
> that, i.e. spit out something like:
>
> const unsigned char dtb[] = {
>  0xaa, 0x55, ......
> };
>
> That'd certainly drastically simplify the makefile, although waste a little
> more time and temp disk space.

What, and withdraw my Makefile contest entry? :-)

I feel that objcopy is designed to do exactly this, and generating C
code is a roundabout way of producing an object file with data in it.
The difficulty of finding out the output format/architecture is
something we might clean up in U-Boot generally at some point (e.g.
figure it out as part of the original 'make ..._config') in which case
this would all go away.

Thoughts?

Regards,
Simon

>
> --
> nvpublic
>
>