linux-kernel - [PATCH 7/7] MIPS: boot: rebuild ITB when contained DTB is updated

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Message-Id: <1523890067-13641-8-git-send-email-yamada.masahiro@socionext.com>
Date:   Mon, 16 Apr 2018 23:47:47 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>, linux-mips@...ux-mips.org
Cc:     Paul Burton <paul.burton@...s.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 7/7] MIPS: boot: rebuild ITB when contained DTB is updated

Since now, the unnecessary rebuild of ITB has been fixed.  Another
problem to be taken care of is, missed rebuild of ITB.

For example, board-boston.its.S includes boston.dtb by the /incbin/
directive.  If boston.dtb is updated, vmlinux.*.dtb must be rebuilt.
Currently, the dependency between ITB and contained DTB files is not
described anywhere.  Previously, this problem was hidden since
vmlinux.*.itb was always rebuilt even if nothing is updated.  By
fixing the spurious rebuild, this is a real problem now.

Use the same strategy for automatic generation of the header file
dependency.  DTC works as a backend of mkimage, and DTC supports -d
option.  It outputs the dependencies, including binary files pulled
by the /incbin/ directive.

The implementation is simpler than cmd_dtc in scripts/Makefile.lib
since we do not need CPP here.  Just pass -d $(depfile) to DTC, and
let the resulted $(depfile) processed by fixdep.

It might be unclear why "$(obj)/dts/%.dtb: ;" is needed.  With this
commit, *.cmd files will contain dependency on DTB files.  In the
next invocation of build, the *.cmd files will be included, then
Make will try to find a rule to update *.dtb files.  Unfortunately,
it is found in scripts/Makefile.lib.  The build rule of $(obj)/%.dtb
is invoked by if_changed_dep, so it needs to include *.cmd files
of DTB, but they are not included because we are in arch/mips/boot,
but those *.cmd files reside in arch/mips/boot/dts/*/.  Cancel the
pattern rule in scripts/Makefile.lib to suppress unneeded rebuilding
of DTB.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 arch/mips/boot/Makefile | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/mips/boot/Makefile b/arch/mips/boot/Makefile
index d102d53..f8dce5b 100644
--- a/arch/mips/boot/Makefile
+++ b/arch/mips/boot/Makefile
@@ -163,11 +163,18 @@ quiet_cmd_itb-image = ITB     $@
 		$(CONFIG_SHELL) $(MKIMAGE) \
 		-D "-I dts -O dtb -p 500 \
 			--include $(objtree)/arch/mips \
-			--warning no-unit_address_vs_reg" \
+			--warning no-unit_address_vs_reg \
+			-d $(depfile)" \
 		-f $(2) $@

 $(obj)/vmlinux.itb: $(obj)/vmlinux.its $(obj)/vmlinux.bin FORCE
-	$(call if_changed,itb-image,$<)
+	$(call if_changed_dep,itb-image,$<)

 $(obj)/vmlinux.%.itb: $(obj)/vmlinux.%.its $(obj)/vmlinux.bin.% FORCE
-	$(call if_changed,itb-image,$<)
+	$(call if_changed_dep,itb-image,$<)
+
+# The -d option of DTC outputs dependencies of binaries included by the
+# /incbin/ directive.  When .*.cmd files are included, Kbuild tries to
+# update *.dtb because it sees a pattern rule defined in scripts/Makefile.lib.
+# The rule must be cancelled by a more specific rule.
+$(obj)/dts/%.dtb: ;
-- 
2.7.4