[PATCH] of: Kconfig: OF_OVERLAY, select OF_EARLY_FLATTREE

[frowand . list]

From: Frank Rowand <frank.rowand@xxxxxxxx>

kbuild test robot reported a new warning for a recent patch:
>> drivers/of/overlay.c:832:2: error: implicit declaration of function 'of_fdt_unflatten_tree' [-Werror=implicit-function-declaration]
     of_fdt_unflatten_tree(new_fdt, NULL, &overlay_root);

The cause is that the prototype for of_fdt_unflatten_tree() in
include/linux/of_fdt.c is guarded by OF_EARLY_FLATTREE.

This was a pre-existing problem for any overlay related caller of
of_fdt_unflatten_device_tree(), who was then going to pass the
unflattened tree to of_overlay_apply().  After the patch that triggered
this warning, all other overlay callers of of_fdt_unflatten_device_tree()
no longer exist, so adding the select to OF_OVERLAY is a sufficient fix.

To reproduce the warning:
  Use the .config attached to https://lkml.org/lkml/2018/2/17/268
  make ARCH=i386 olddefconfig
  make ARCH=i386 CC=gcc-7 drivers/of/overlay.o

Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>
---
 drivers/of/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 783e0870bd22..00a6abfaaec7 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -92,6 +92,7 @@ config OF_RESOLVE
 config OF_OVERLAY
 	bool "Device Tree overlays"
 	select OF_DYNAMIC
+	select OF_EARLY_FLATTREE
 	select OF_RESOLVE
 	help
 	  Overlays are a method to dynamically modify part of the kernel's
-- 
Frank Rowand <frank.rowand@xxxxxxxx>