tools: PCI: Change pcitest compiling process

Change tool compiling process in order to be build using the same
mechanism used in other linux tools (e.g. iio, perf, etc). This will
allow in future the buildroot tool to build and integrate this tool in
a more expeditious way.

Update documentation accordingly.

Signed-off-by: Gustavo Pimentel <[email protected]>
Signed-off-by: Lorenzo Pieralisi <[email protected]>
Reviewed-by: Kishon Vijay Abraham I <[email protected]>

tools/pci/Build

@@ -0,0 +1 @@
+pcitest-y += pcitest.o

tools/pci/Makefile

@@ -0,0 +1,53 @@
+# SPDX-License-Identifier: GPL-2.0
+include ../scripts/Makefile.include
+
+bindir ?= /usr/bin
+
+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
+# Do not use make's built-in rules
+# (this improves performance and avoids hard-to-debug behaviour);
+MAKEFLAGS += -r
+
+CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
+
+ALL_TARGETS := pcitest pcitest.sh
+ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
+
+all: $(ALL_PROGRAMS)
+
+export srctree OUTPUT CC LD CFLAGS
+include $(srctree)/tools/build/Makefile.include
+
+#
+# We need the following to be outside of kernel tree
+#
+$(OUTPUT)include/linux/: ../../include/uapi/linux/
+	mkdir -p $(OUTPUT)include/linux/ 2>&1 || true
+	ln -sf $(CURDIR)/../../include/uapi/linux/pcitest.h $@
+
+prepare: $(OUTPUT)include/linux/
+
+PCITEST_IN := $(OUTPUT)pcitest-in.o
+$(PCITEST_IN): prepare FORCE
+	$(Q)$(MAKE) $(build)=pcitest
+$(OUTPUT)pcitest: $(PCITEST_IN)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
+
+clean:
+	rm -f $(ALL_PROGRAMS)
+	rm -rf $(OUTPUT)include/
+	find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.d' -delete
+
+install: $(ALL_PROGRAMS)
+	install -d -m 755 $(DESTDIR)$(bindir);		\
+	for program in $(ALL_PROGRAMS); do		\
+		install $$program $(DESTDIR)$(bindir);	\
+	done
+
+FORCE:
+
+.PHONY: all install clean FORCE prepare