kconfig-package: add support for config fragments

Adds functionality to the kconfig infrastructure to merge additional
configuration fragment files to the main configuration file of
kconfig packages, using support/kconfig/merge_config.sh

Typical use-case is when you want your configuration to be
kept in sync with an upstream (def)config file, but do require
some minor local modifications.

Disables -update-config and -update-defconfig targets when
fragment files are set.

[Thomas: take into account comments made by Arnout:
  - Minor fixes in the documentation changes
  - Add @ before the tests done in the $(1)-update-config and
    $(1)-update-defconfig targets.]

Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Tested-by: Gergely Imreh <imrehg@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/docs/manual/adding-packages-kconfig.txt b/docs/manual/adding-packages-kconfig.txt
index e87d393070..17f91e3f2d 100644
--- a/docs/manual/adding-packages-kconfig.txt
+++ b/docs/manual/adding-packages-kconfig.txt
@@ -34,8 +34,14 @@ This snippet creates the following make targets:
 
 * +foo-menuconfig+, which calls the package's +menuconfig+ target
 
-* +foo-update-config+, which copies the configuration back to the source
-  configuration file.
+* +foo-update-config+, which copies the configuration back to the
+  source configuration file. It is not possible to use this target
+  when fragment files are set.
+
+* +foo-update-defconfig+, which copies the configuration back to the
+  source configuration file. The configuration file will only list the
+  options that differ from the default values. It is not possible to
+  use this target when fragment files are set.
 
 and ensures that the source configuration file is copied to the build
 directory at the right moment.
@@ -46,6 +52,11 @@ be set to suit the needs of the package under consideration:
 * +FOO_KCONFIG_EDITORS+: a space-separated list of kconfig editors to
   support, for example 'menuconfig xconfig'. By default, 'menuconfig'.
 
+* +FOO_KCONFIG_FRAGMENT_FILES+: a space-separated list of configuration
+  fragment files that are merged to the main configuration file.
+  Fragment files are typically used when there is a desire to stay in sync
+  with an upstream (def)config file, with some minor modifications.
+
 * +FOO_KCONFIG_OPTS+: extra options to pass when calling the kconfig
   editors. This may need to include '$(FOO_MAKE_OPTS)', for example. By
   default, empty.