of: Add support for linking device tree blobs into vmlinux

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@gmail.com>
Acked-by: Michal Marek <mmarek@suse.cz>
[grant.likely@secretlab.ca: cleaned up whitespace inconsistencies]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 0ef00bd6e54d..86e3cd0d26a0 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 cmd,dtc)
 
 --- 6.7 Custom kbuild commands