kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

  $(obj)     - directory in the object tree
  $(src)     - directory in the source tree  (changed by this commit)
  $(objtree) - the top of the kernel object tree
  $(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

1 files changed, 4 insertions, 6 deletions

diff --git a/drivers/gpu/drm/nouveau/Kbuild b/drivers/gpu/drm/nouveau/Kbuild
index cf6b3a80c0c8..c32c01827c1d 100644
--- a/drivers/gpu/drm/nouveau/Kbuild
+++ b/drivers/gpu/drm/nouveau/Kbuild
@@ -1,10 +1,8 @@
-NOUVEAU_PATH ?= $(srctree)
-
 # SPDX-License-Identifier: MIT
-ccflags-y += -I $(NOUVEAU_PATH)/$(src)/include
-ccflags-y += -I $(NOUVEAU_PATH)/$(src)/include/nvkm
-ccflags-y += -I $(NOUVEAU_PATH)/$(src)/nvkm
-ccflags-y += -I $(NOUVEAU_PATH)/$(src)
+ccflags-y += -I $(src)/include
+ccflags-y += -I $(src)/include/nvkm
+ccflags-y += -I $(src)/nvkm
+ccflags-y += -I $(src)
 
 # NVKM - HW resource manager
 #- code also used by various userspace tools/tests