Makefiles: some contortions to be friends of submodules

This patch adds a script "check-fmc-bus" that returns the pathname of
the fmc-bus kernel driver, either under this directory or under
../fmc-bus .  The former applies when fmc-bus is a submodule of this
package, the latter applies when we both are submodules of another
package.

The final aim is helping the naive user, who just wants to build it
all in a single step -- both if building this package or another
package that depends on both fmc-bus and this one.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Makefile

 
-DIRS = fmc-bus/kernel kernel tools doc
+# We have a problem here: this package may be a submodule of something
+# else (for example: fine-delay). If this is the case, fmc-bus is on ../
+# This external script returns the pathname of the "kernel" subdir of fmc-bus
+FMC_DRV = $(./check-fmc-bus)
+
+DIRS = $(FMC_DRV) kernel tools
 
 all clean modules install modules_install:
 	for d in $(DIRS); do $(MAKE) -C $$d $@ || exit 1; done

check-fmc-bus

+#!/bin/sh
+
+cd $(dirname $0)
+
+# If this project _and_ fmc-bus are submodules of ../, pick ../fmc-bus
+
+FMC_SUBDIR=$(/bin/pwd)/fmc-bus/kernel
+FMC_DOTDOT=$(/bin/pwd)/../fmc-bus/kernel
+
+THIS=$(basename $(/bin/pwd))
+
+if ! test -f ../.gitmodules; then
+    echo $FMC_SUBDIR
+    exit 0
+fi
+
+if ! grep "submodule \"$THIS\"" ../.gitmodules > /dev/null; then
+    echo $FMC_SUBDIR
+    exit 0
+fi
+
+if ! grep "submodule \"fmc-bus\"" ../.gitmodules > /dev/null; then
+    echo $FMC_SUBDIR
+    exit 0
+fi
+
+echo $FMC_DOTDOT
\ No newline at end of file

kernel/Makefile

 
 LINUX ?= /lib/modules/$(shell uname -r)/build
 
-KBUILD_EXTRA_SYMBOLS := $M/../fmc-bus/kernel/Module.symvers
+FMC_DRV ?= $(shell $M/../check-fmc-bus)
 
-ccflags-y += -I$M/include -I$M/../fmc-bus/kernel/include
+KBUILD_EXTRA_SYMBOLS := $(FMC_DRV)/Module.symvers
+
+ccflags-y += -I$M/include -I$(FMC_DRV)/include
 ccflags-y += $(WR_NIC_CFLAGS)
 
 obj-m += spec.o