Re: [PATCH 1/4] of: Add support for linking device tree blobs intovmlinux

From: Sam Ravnborg
Date: Mon Dec 06 2010 - 14:03:04 EST

On Mon, Dec 06, 2010 at 09:35:59AM -0800, dirk.brandewie@xxxxxxxxx wrote:
> From: Dirk Brandewie <dirk.brandewie@xxxxxxxxx>
>
> This patch adds support for linking device tree blob(s) into
> vmlinux. Modifies asm-generic/vmlinux.lds.h to add linking
> .dtb sections into vmlinux. To maintain compatiblity with the of/fdt
> driver code platforms MUST copy the blob to a non-init memory location
> before the kernel frees the .init.* sections in the 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.
>
> STRUCT_ALIGNMENT is defined in vmlinux.lds.h for use in the rule to
> create wrapper objects for the dtb in Makefile.lib. The
> STRUCT_ALIGN() macro in vmlinux.lds.h is modified to use the
> STRUCT_ALIGNMENT definition.
>
> 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@xxxxxxxxx>
> ---
> Documentation/kbuild/makefiles.txt | 15 +++++++++++++++
> include/asm-generic/vmlinux.lds.h | 15 ++++++++++++---
> scripts/Makefile.lib | 21 ++++++++++++++++++++-
> 3 files changed, 47 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
> index 0ef00bd..fc18bb1 100644
> --- a/Documentation/kbuild/makefiles.txt
> +++ b/Documentation/kbuild/makefiles.txt
> @@ -1136,6 +1136,21 @@ When kbuild executes, the following steps are followed (roughly):
> resulting in the target file being recompiled for no
> obvious reason.
>
> + dtc
> + Create flattend device tree blob object suitable for linking
> + into vmlinux. Device tree blobs linked into vmlinux are placed
> + in an init section in the image. Platform code *must* copy the
> + blob to non-init memory prior to calling unflatten_device_tree().
> +
> + Example:
> + #arch/x86/platform/ce4100/Makefile
> + clean-files := *dtb.S
> +
> + DTC_FLAGS := -p 1024
> + obj-y += foo.dtb.o
> +
> + $(obj)/%.dtb: $(src)/%.dts
> + $(call if_changed,dtc)

When using "if_changed" you need to add your target to targets-y.
And you need to specify FORCE as a prerequisite to force kbuild
to use the if_changed logic.

The purpose of if_changed is to check if the commandlien has changed
and execute the command again also if the commandline has changed.
The simpler variant is $(call cmd,dtc) where you do not check
the command line and do not need FORCE.

> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index bd69d79..024d3b9 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -23,7 +23,7 @@
> * _etext = .;
> *
> * _sdata = .;
> - * RO_DATA_SECTION(PAGE_SIZE)
> +* RO_DATA_SECTION(PAGE_SIZE)
> * RW_DATA_SECTION(...)
> * _edata = .;
> *

Change seems wrong.

> @@ -67,7 +67,8 @@
> * 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)
>
> /* The actual configuration determine if the init/exit sections
> * are handled as text/data or they can be discarded (which
> @@ -146,6 +147,13 @@
> #define TRACE_SYSCALLS()
> #endif
>
> +
> +#define KERNEL_DTB() \
> + STRUCT_ALIGN(); \
> + VMLINUX_SYMBOL(__dtb_start) = .; \
> + *(.dtb.init.rodata) \
> + VMLINUX_SYMBOL(__dtb_end) = .;
> +
> /* .data section */
> #define DATA_DATA \
> *(.data) \
> @@ -468,7 +476,8 @@
> MCOUNT_REC() \
> DEV_DISCARD(init.rodata) \
> CPU_DISCARD(init.rodata) \
> - MEM_DISCARD(init.rodata)
> + MEM_DISCARD(init.rodata) \
> + KERNEL_DTB()
>
> #define INIT_TEXT \
> *(.init.text) \
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 4c72c11..937eabbb 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -200,7 +200,26 @@ quiet_cmd_gzip = GZIP $@
> cmd_gzip = (cat $(filter-out FORCE,$^) | gzip -f -9 > $@) || \
> (rm -f $@ ; false)
>
> -
> +# DTC
> +# ---------------------------------------------------------------------------
> +
> +# Generate an assembly file to wrap the output of the device tree compiler
> +$(obj)/%.dtb.S: $(obj)/%.dtb
> + @echo '#include <asm-generic/vmlinux.lds.h>' > $@
> + @echo '.section .dtb.init.rodata,"a"' >> $@
> + @echo '.balign STRUCT_ALIGNMENT' >> $@
> + @echo '.global __dtb_$(*F)_begin' >> $@
> + @echo '__dtb_$(*F)_begin:' >> $@
> + @echo '.incbin "$<" ' >> $@
> + @echo '__dtb_$(*F)_end:' >> $@
> + @echo '.global __dtb_$(*F)_end' >> $@
> + @echo '.balign STRUCT_ALIGNMENT' >> $@
> +

If we really want this rule in Makefile.lib then at least make it less verbose,
and more secure.
Something like this:
quiet_dt_S_dtb_cmd = DTB $@
dt_S_dtb_cmd = \
( \
@echo '#include <asm-generic/vmlinux.lds.h>'; \
@echo '.section .dtb.init.rodata,"a"'; \
@echo '.balign STRUCT_ALIGNMENT'; \
echo '.global __dtb_$(*F)_begin'; \
echo '__dtb_$(*F)_begin:'; \
echo '.incbin "$<" '; \
echo '__dtb_$(*F)_end:'; \
echo '.global __dtb_$(*F)_end'; \
echo '.balign STRUCT_ALIGNMENT'; \
) > $@

$(obj)/%.dtb.S: $(obj)/%.dtb
$(call cmd,dt_S_dtb)


> +DTC = $(objtree)/scripts/dtc/dtc

If this is the only spot where we use DTC then drop the variable.

> +
> +quiet_cmd_dtc = DTC $@
> + cmd_dtc = $(DTC) -O dtb -o $@ -b 0 $(DTC_FLAGS) $<


> +ooo

What is the purpose of these "ooo"? A debugging left-over?


Sam
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