linux-kernel - Re: [PATCH 1/5] of: Add support for linking device tree blobs into vmlinux

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Date:	Wed, 17 Nov 2010 10:27:51 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	dirk.brandewie@...il.com, Michal Marek <mmarek@...e.cz>
Cc:	devicetree-discuss@...ts.ozlabs.org, sodaville@...utronix.de,
	arjan@...ux.intel.com, linuxppc-dev@...ts.ozlabs.org,
	microblaze-uclinux@...e.uq.edu.au, linux-arch@...r.kernel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] of: Add support for linking device tree blobs into
	vmlinux

On Tue, Nov 16, 2010 at 02:41:36PM -0800, dirk.brandewie@...il.com wrote:
> From: Dirk Brandewie <dirk.brandewie@...il.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@...il.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)

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

	Sam
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