diff --git a/tools/gpio/.gitignore b/tools/gpio/.gitignore
index 9e9dd4b..a94c0e8 100644
--- a/tools/gpio/.gitignore
+++ b/tools/gpio/.gitignore
@@ -1,4 +1,4 @@
 gpio-event-mon
 gpio-hammer
 lsgpio
-
+include/linux/gpio.h
diff --git a/tools/gpio/Build b/tools/gpio/Build
index 620c193..4141f35 100644
--- a/tools/gpio/Build
+++ b/tools/gpio/Build
@@ -1,3 +1,4 @@
+gpio-utils-y += gpio-utils.o
 lsgpio-y += lsgpio.o gpio-utils.o
 gpio-hammer-y += gpio-hammer.o gpio-utils.o
 gpio-event-mon-y += gpio-event-mon.o gpio-utils.o
diff --git a/tools/gpio/Makefile b/tools/gpio/Makefile
index 240eda0..6080de5 100644
--- a/tools/gpio/Makefile
+++ b/tools/gpio/Makefile
@@ -3,7 +3,11 @@
 
 bindir ?= /usr/bin
 
-ifeq ($(srctree),)
+# This will work when gpio is built in tools env. where srctree
+# isn't set and when invoked from selftests build, where srctree
+# is set to ".". building_out_of_srctree is undefined for in srctree
+# builds
+ifndef building_out_of_srctree
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
@@ -12,7 +16,7 @@
 # (this improves performance and avoids hard-to-debug behaviour);
 MAKEFLAGS += -r
 
-CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
+override CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
 
 ALL_TARGETS := lsgpio gpio-hammer gpio-event-mon
 ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
@@ -31,11 +35,15 @@
 
 prepare: $(OUTPUT)include/linux/gpio.h
 
+GPIO_UTILS_IN := $(output)gpio-utils-in.o
+$(GPIO_UTILS_IN): prepare FORCE
+	$(Q)$(MAKE) $(build)=gpio-utils
+
 #
 # lsgpio
 #
 LSGPIO_IN := $(OUTPUT)lsgpio-in.o
-$(LSGPIO_IN): prepare FORCE
+$(LSGPIO_IN): prepare FORCE $(OUTPUT)gpio-utils-in.o
 	$(Q)$(MAKE) $(build)=lsgpio
 $(OUTPUT)lsgpio: $(LSGPIO_IN)
 	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
@@ -44,7 +52,7 @@
 # gpio-hammer
 #
 GPIO_HAMMER_IN := $(OUTPUT)gpio-hammer-in.o
-$(GPIO_HAMMER_IN): prepare FORCE
+$(GPIO_HAMMER_IN): prepare FORCE $(OUTPUT)gpio-utils-in.o
 	$(Q)$(MAKE) $(build)=gpio-hammer
 $(OUTPUT)gpio-hammer: $(GPIO_HAMMER_IN)
 	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
@@ -53,7 +61,7 @@
 # gpio-event-mon
 #
 GPIO_EVENT_MON_IN := $(OUTPUT)gpio-event-mon-in.o
-$(GPIO_EVENT_MON_IN): prepare FORCE
+$(GPIO_EVENT_MON_IN): prepare FORCE $(OUTPUT)gpio-utils-in.o
 	$(Q)$(MAKE) $(build)=gpio-event-mon
 $(OUTPUT)gpio-event-mon: $(GPIO_EVENT_MON_IN)
 	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
diff --git a/tools/gpio/gpio-event-mon.c b/tools/gpio/gpio-event-mon.c
index c864544..30ed0e0 100644
--- a/tools/gpio/gpio-event-mon.c
+++ b/tools/gpio/gpio-event-mon.c
@@ -1,12 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * gpio-event-mon - monitor GPIO line events from userspace
  *
  * Copyright (C) 2016 Linus Walleij
  *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
- *
  * Usage:
  *	gpio-event-mon -n <device-name> -o <offset>
  */
diff --git a/tools/gpio/gpio-hammer.c b/tools/gpio/gpio-hammer.c
index 4bcb234..0e0060a 100644
--- a/tools/gpio/gpio-hammer.c
+++ b/tools/gpio/gpio-hammer.c
@@ -1,12 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * gpio-hammer - example swiss army knife to shake GPIO lines on a system
  *
  * Copyright (C) 2016 Linus Walleij
  *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
- *
  * Usage:
  *	gpio-hammer -n <device-name> -o <offset1> -o <offset2>
  */
diff --git a/tools/gpio/gpio-utils.c b/tools/gpio/gpio-utils.c
index cf7e2f3..53470de 100644
--- a/tools/gpio/gpio-utils.c
+++ b/tools/gpio/gpio-utils.c
@@ -1,12 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * GPIO tools - helpers library for the GPIO tools
  *
  * Copyright (C) 2015 Linus Walleij
  * Copyright (C) 2016 Bamvor Jian Zhang
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
  */
 
 #include <unistd.h>
diff --git a/tools/gpio/gpio-utils.h b/tools/gpio/gpio-utils.h
index 344ea04..cf37f13 100644
--- a/tools/gpio/gpio-utils.h
+++ b/tools/gpio/gpio-utils.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * GPIO tools - utility helpers library for the GPIO tools
  *
@@ -7,9 +8,6 @@
  * Copyright (c) 2010 Manuel Stahl <manuel.stahl@iis.fraunhofer.de>
  * Copyright (c) 2008 Jonathan Cameron
  * *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
  */
 #ifndef _GPIO_UTILS_H_
 #define _GPIO_UTILS_H_
diff --git a/tools/gpio/lsgpio.c b/tools/gpio/lsgpio.c
index eb3f56e..e1430f5 100644
--- a/tools/gpio/lsgpio.c
+++ b/tools/gpio/lsgpio.c
@@ -1,12 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * lsgpio - example on how to list the GPIO lines on a system
  *
  * Copyright (C) 2015 Linus Walleij
  *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
- *
  * Usage:
  *	lsgpio <-n device-name>
  */