[U-Boot] [PATCH V2] Makefile: remove BUILD_TAG from KBUILD_CFLAGS

[Stephen Warren]

From: Stephen Warren <swarren at nvidia.com>

If BUILD_TAG is part of KBUILD_CFLAGS, then any time the value changes,
all files get rebuilt. In a continuous integration environment, the value
will change every build. This wastes time, assuming that incremental
builds would otherwise occur.

To solve this, remove BUILD_TAG from KBUILD_CFLAGS and add it to CFLAGS
for just the one file that uses it. This does have the disadvantage that
if any other files want to use the flag, we'll need to duplicate this
custom CFLAGS setup logic. However, it seems unlikely we'll need this.

An alternative would be to add BUILD_TAG to the "local version" and remove
the special case code from display_options.c. However, that would affect
the format of the U-Boot signon message, which may negatively affect
people looking for specific data there. The approach of using
file-specific CFLAGS was suggested by Masahiro Yamada.

Signed-off-by: Stephen Warren <swarren at nvidia.com>
---
v2: Set CFLAGS on display_options.c rather than modifying
scripts/setlocalversion to add BUILD_TAG to the local version.
---
 Makefile     | 4 ----
 lib/Makefile | 2 +-
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index 42fad45afee1..2265b8995a7b 100644
--- a/Makefile
+++ b/Makefile
@@ -562,10 +562,6 @@ else
 KBUILD_CFLAGS	+= -O2
 endif
 
-ifdef BUILD_TAG
-KBUILD_CFLAGS += -DBUILD_TAG='"$(BUILD_TAG)"'
-endif
-
 KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
 KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks)
 
diff --git a/lib/Makefile b/lib/Makefile
index dd36f25b2a32..d4491b8319f5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -67,7 +67,7 @@ obj-$(CONFIG_ADDR_MAP) += addr_map.o
 obj-y += hashtable.o
 obj-y += errno.o
 obj-y += display_options.o
-obj-$(CONFIG_BCH) += bch.o
+CFLAGS_display_options.o := $(if $(BUILD_TAG),-DBUILD_TAG='"$(BUILD_TAG)"')
 obj-y += crc32.o
 obj-y += ctype.o
 obj-y += div64.o
-- 
2.7.0