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:

quoted

From: Dirk Brandewie <redacted>

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 <redacted>
---
 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.

quoted

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.

quoted

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.

quoted

+
+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 $@)

quoted

+      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.

quoted

+
+$(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.