[PATCH 3/4] selftests/gpio: Fix build when source tree is read only

[Michael Ellerman <mpe@xxxxxxxxxxxxxx>]

Currently the gpio selftests fail to build if the source tree is read
only:

  make -j 160 -C tools/testing/selftests TARGETS=gpio
  make[1]: Entering directory '/linux/tools/testing/selftests/gpio'
  make OUTPUT=/linux/tools/gpio/ -C /linux/tools/gpio
  make[2]: Entering directory '/linux/tools/gpio'
  mkdir -p /linux/tools/gpio/include/linux 2>&1 || true
  ln -sf /linux/tools/gpio/../../include/uapi/linux/gpio.h /linux/tools/gpio/include/linux/gpio.h
  ln: failed to create symbolic link '/linux/tools/gpio/include/linux/gpio.h': Read-only file system

This happens because we ask make to build ../../../gpio (tools/gpio)
without pointing OUTPUT away from the source directory.

To fix it we create a subdirectory of the existing OUTPUT directory,
called tools-gpio, and tell tools/gpio to build in there.

Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
---
 tools/testing/selftests/gpio/Makefile | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/gpio/Makefile b/tools/testing/selftests/gpio/Makefile
index 615c8a953ade..acf4088a9891 100644
--- a/tools/testing/selftests/gpio/Makefile
+++ b/tools/testing/selftests/gpio/Makefile
@@ -17,14 +17,18 @@ KSFT_KHDR_INSTALL := 1
 include ../lib.mk
 
 GPIODIR := $(realpath ../../../gpio)
-GPIOOBJ := gpio-utils.o
+GPIOOUT := $(OUTPUT)/tools-gpio/
+GPIOOBJ := $(GPIOOUT)/gpio-utils.o
 
 override define CLEAN
 	$(RM) $(TEST_GEN_PROGS_EXTENDED)
-	$(MAKE) -C $(GPIODIR) OUTPUT=$(GPIODIR)/ clean
+	$(RM) -rf $(GPIOOUT)
 endef
 
-$(TEST_GEN_PROGS_EXTENDED): $(GPIODIR)/$(GPIOOBJ)
+$(TEST_GEN_PROGS_EXTENDED): $(GPIOOBJ)
 
-$(GPIODIR)/$(GPIOOBJ):
-	$(MAKE) OUTPUT=$(GPIODIR)/ -C $(GPIODIR)
+$(GPIOOUT):
+	mkdir -p $@
+
+$(GPIOOBJ): $(GPIOOUT)
+	$(MAKE) OUTPUT=$(GPIOOUT) -C $(GPIODIR)
-- 
2.25.1