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SubjectRe: [PATCH 1/5] of: Add support for linking device tree blobs into vmlinux
On Wed, Nov 17, 2010 at 10:27:51AM +0100, Sam Ravnborg wrote:
> On Tue, Nov 16, 2010 at 02:41:36PM -0800, dirk.brandewie@gmail.com wrote:
> > From: Dirk Brandewie <dirk.brandewie@gmail.com>
> >
> > This patch adds support for linking device tree blobs into
> > vmlinux. Modifies asm-generic/vmlinux.lds.h to add linking
> > .dtb.init.rodata sections into the .init.data section of the vmlinux
> > image. Modifies scripts/Makefile.lib to add a kbuild command to
> > compile DTS files to device tree blobs and a rule to create objects to
> > wrap the blobs for linking.
> >
> > The DTB's are placed on 32 byte boundries to allow parsing the blob
> > with driver/of/fdt.c during early boot without having to copy the blob
> > to get the structure alignment GCC expects.
> >
> > A DTB is linked in by adding the DTB object to the list of objects to
> > be linked into vmlinux in the archtecture specific Makefile using
> > obj-y += foo.dtb.o
> >
> > Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
> > ---
> > include/asm-generic/vmlinux.lds.h | 19 +++++++++++++++++--
> > scripts/Makefile.lib | 20 ++++++++++++++++++++
> > 2 files changed, 37 insertions(+), 2 deletions(-)
>
> When you touch Makefiles in scripts/* it is always a good idea to cc:
> kbuild maintainer on the patch - I have added Michal.
>
> Support functionality in Makefile.lib is documented in
> Documentation/kbuild/* - please add documentation there.
>
> >
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index bd69d79..ea671e7 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -67,7 +67,14 @@
> > * Align to a 32 byte boundary equal to the
> > * alignment gcc 4.5 uses for a struct
> > */
> > -#define STRUCT_ALIGN() . = ALIGN(32)
> > +#define STRUCT_ALIGNMENT 32
> > +#define STRUCT_ALIGN() . = ALIGN(STRUCT_ALIGNMENT)
> > +
> > +/* Device tree blobs linked into the kernel need to have proper
> > + * structure alignment to be parsed by the flat device tree library
> > + * used in early boot
> > +*/
> > +#define DTB_ALIGNMENT STRUCT_ALIGNMENT
>
> It has been discussed in another thread some time ago to move
> to a general 32 byte alignment for everything in vmlinux.lds.h
> So there is not much need for the specific DTB alignment.
>
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 4c72c11..29db062 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -200,6 +200,26 @@ quiet_cmd_gzip = GZIP $@
> > cmd_gzip = (cat $(filter-out FORCE,$^) | gzip -f -9 > $@) || \
> > (rm -f $@ ; false)
> >
> > +# DTC
> > +# ---------------------------------------------------------------------------
> > +$(obj)/%.dtb.S: $(obj)/%.dtb FORCE
> > + @echo '#include <asm-generic/vmlinux.lds.h>' > $@
> > + @echo '.section .dtb.init.rodata,"a"' >> $@
> > + @echo '.balign DTB_ALIGNMENT' >> $@
> > + @echo '.global __dtb_$(*F)_begin' >> $@
> > + @echo '__dtb_$(*F)_begin:' >> $@
> > + @echo '.incbin "$<" ' >> $@
> > + @echo '__dtb_$(*F)_end:' >> $@
> > + @echo '.global __dtb_$(*F)_end' >> $@
> > + @echo '.balign DTB_ALIGNMENT' >> $@
>
>
> This will be noisy during build. Please use proper macors to supress output.
>
>
> > +
> > +DTC = $(objtree)/scripts/dtc/dtc
> > +
> > +quiet_cmd_dtc = DTC $@
> Please avoid tabs in the output - all other uses spaces. (There is a tab between DTC and $@)
>
> > + cmd_dtc = $(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(src)/dts/$*.dts
>
> Looks strange. How about:
> cmd_dtc = $(DTC) -O dtb -o $@ -b 0 $(DTS_FLAGS) $<
>
> Then you avoid the hardcoded path in the rule too.
>
>
> > +
> > +$(obj)/%.dtb: $(src)/dts/%.dts
> > + $(call if_changed,dtc)

The rule should be generic (not depend on the presence of a dts
subdirectory. Basically, the .dtb really should be generated in the
same directory as the .dts file. There is no reason for this rule to
have special behaviour.

>
> This snippet belong in the file that uses this.
> This is how we do for other rules like bzip etc.

This rule is intended to be generic and usable anywhere in the tree.

g.



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