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>

3 files changed, 49 insertions, 2 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
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index bd69d79208de..05cbad03c5ab 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -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 4c72c1189479..396da16aabf8 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -200,6 +200,29 @@ 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
+quiet_cmd_dt_S_dtb= DTB    $@
+cmd_dt_S_dtb=                                           \
+(                                                       \
+        echo '\#include <asm-generic/vmlinux.lds.h>';   \
+        echo '.section .dtb.init.rodata,"a"';           \
+        echo '.balign STRUCT_ALIGNMENT';                \
+        echo '.global __dtb_$(*F)_begin';               \
+        echo '__dtb_$(*F)_begin:';                      \
+        echo '.incbin "$<" ';                           \
+        echo '__dtb_$(*F)_end:';                        \
+        echo '.global __dtb_$(*F)_end';                 \
+        echo '.balign STRUCT_ALIGNMENT';                \
+) > $@
+
+$(obj)/%.dtb.S: $(obj)/%.dtb
+        $(call cmd,dt_S_dtb)
+
+quiet_cmd_dtc = DTC     $@
+cmd_dtc = $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) $<
 
 # Bzip2
 # ---------------------------------------------------------------------------