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

[Stephen Warren]

Simon Glass wrote at Thursday, October 13, 2011 3:25 PM:
> 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?

Looking some more, dtc has option "-O asm" which writes directly to a text
file that can be assembled; there'd be no extra temp files or conversions
if you used that.

-- 
nvpublic