+.. SPDX-License-Identifier: GPL-2.0-or-later
+
Kconfig in U-Boot
=================
The conventional configuration was replaced by Kconfig at v2014.10-rc1 release.
-
Language Specification
----------------------
-Kconfig originates in Linux Kernel.
-See the file "Documentation/kbuild/kconfig*.txt" in your Linux Kernel
-source directory for a basic specification of Kconfig.
-
+The Kconfig configuration language originates in Linux kernel.
+See the Linux document
+`Kconfig Language <https://www.kernel.org/doc/html/latest/kbuild/kconfig-language.html>`_
+for a description of Kconfig.
Difference from Linux's Kconfig
-------------------------------
Here are some worth-mentioning configuration targets.
-- silentoldconfig
-
+silentoldconfig
This target updates .config, include/generated/autoconf.h and
include/configs/* as in Linux. In U-Boot, it also does the following
for the compatibility with the old configuration system:
* create tpl/include/autoconf.mk (TPL only)
If we could completely switch to Kconfig in a long run
- (i.e. remove all the include/configs/*.h), those additional processings
+ (i.e. remove all the include/configs/\*.h), those additional processings
above would be removed.
-- defconfig
-
+defconfig
In U-Boot, "make defconfig" is a shorthand of "make sandbox_defconfig"
-- <board>_defconfig
-
+<board>_defconfig
Now it works as in Linux.
- The prefixes such as "+S:" in *_defconfig are deprecated.
+ The prefixes such as "+S:" in \*_defconfig are deprecated.
You can simply remove the prefixes. Do not add them for new boards.
-- <board>_config
-
+<board>_config
This does not exist in Linux's Kconfig.
"make <board>_config" works the same as "make <board>_defconfig".
Prior to Kconfig, in U-Boot, "make <board>_config" was used for the
configuration. It is still supported for backward compatibility, so
we do not need to update the distro recipes.
-
The other configuration targets work as in Linux Kernel.
-
Migration steps to Kconfig
--------------------------
When adding a new CONFIG macro, it is highly recommended to add it to Kconfig
rather than to a header file.
-
Conversion from boards.cfg to Kconfig
-------------------------------------
Prior to Kconfig, boards.cfg was a primary database that contained Arch, CPU,
-SoC, etc. of all the supported boards. It was deleted when switching to
-Kconfig. Each field of boards.cfg was converted as follows:
-
- Status -> "S:" entry of MAINTAINERS
- Arch -> CONFIG_SYS_ARCH defined by Kconfig
- CPU -> CONFIG_SYS_CPU defined by Kconfig
- SoC -> CONFIG_SYS_SOC defined by Kconfig
- Vendor -> CONFIG_SYS_VENDOR defined by Kconfig
- Board -> CONFIG_SYS_BOARD defined by Kconfig
- Target -> File name of defconfig (configs/<target>_defconfig)
- Maintainers -> "M:" entry of MAINTAINERS
-
+SoC, etc. of all the supported boards. It was deleted when switching to
+Kconfig. Each field of boards.cfg was converted as follows:
+
+=========== ====================================================
+From To
+=========== ====================================================
+Arch CONFIG_SYS_ARCH defined by Kconfig
+Board CONFIG_SYS_BOARD defined by Kconfig
+CPU CONFIG_SYS_CPU defined by Kconfig
+Maintainers "M:" entry of MAINTAINERS
+SoC CONFIG_SYS_SOC defined by Kconfig
+Status "S:" entry of MAINTAINERS
+Target File name of defconfig (configs/<target>\_defconfig)
+Vendor CONFIG_SYS_VENDOR defined by Kconfig
+=========== ====================================================
Tips to add/remove boards
-------------------------
When adding a new board, the following steps are generally needed:
- [1] Add a header file include/configs/<target>.h
- [2] Make sure to define necessary CONFIG_SYS_* in Kconfig:
- Define CONFIG_SYS_CPU="cpu" to compile arch/<arch>/cpu/<cpu>
- Define CONFIG_SYS_SOC="soc" to compile arch/<arch>/cpu/<cpu>/<soc>
- Define CONFIG_SYS_VENDOR="vendor" to compile board/<vendor>/common/*
- and board/<vendor>/<board>/*
- Define CONFIG_SYS_BOARD="board" to compile board/<board>/*
- (or board/<vendor>/<board>/* if CONFIG_SYS_VENDOR is defined)
- Define CONFIG_SYS_CONFIG_NAME="target" to include
- include/configs/<target>.h
- [3] Add a new entry to the board select menu in Kconfig.
- The board select menu is located in arch/<arch>/Kconfig or
- arch/<arch>/*/Kconfig.
- [4] Add a MAINTAINERS file
- It is generally placed at board/<board>/MAINTAINERS or
- board/<vendor>/<board>/MAINTAINERS
- [5] Add configs/<target>_defconfig
+1. Add a header file include/configs/<target>.h
+
+2. Make sure to define necessary CONFIG_SYS_* in Kconfig:
+
+ * Define CONFIG_SYS_CPU="cpu" to compile arch/<arch>/cpu/<cpu>
+ * Define CONFIG_SYS_SOC="soc" to compile arch/<arch>/cpu/<cpu>/<soc>
+ * Define CONFIG_SYS_VENDOR="vendor" to compile board/<vendor>/common/\*
+ and board/<vendor>/<board>/\*
+ * Define CONFIG_SYS_BOARD="board" to compile board/<board>/\*
+ (or board/<vendor>/<board>/* if CONFIG_SYS_VENDOR is defined)
+ Define CONFIG_SYS_CONFIG_NAME="target" to include
+ include/configs/<target>.h
+
+3. Add a new entry to the board select menu in Kconfig.
+ The board select menu is located in arch/<arch>/Kconfig or
+ arch/<arch>/\*/Kconfig.
+
+4. Add a MAINTAINERS file
+ It is generally placed at board/<board>/MAINTAINERS or
+ board/<vendor>/<board>/MAINTAINERS
+
+5. Add configs/<target>_defconfig
When removing an obsolete board, the following steps are generally needed:
- [1] Remove configs/<target>_defconfig
- [2] Remove include/configs/<target>.h if it is not used by any other boards
- [3] Remove board/<vendor>/<board>/* or board/<board>/* if it is not used
- by any other boards
- [4] Update MAINTAINERS if necessary
- [5] Remove the unused entry from the board select menu in Kconfig
- [6] Add an entry to doc/README.scrapyard
+1. Remove configs/<target>_defconfig
+
+2. Remove include/configs/<target>.h if it is not used by any other boards
+
+3. Remove board/<vendor>/<board>/\* or board/<board>/\* if it is not used
+ by any other boards
+
+4. Update MAINTAINERS if necessary
+
+5. Remove the unused entry from the board select menu in Kconfig
+6. Add an entry to doc/README.scrapyard
TODO
----
-- In the pre-Kconfig, a single board had multiple entries in the boards.cfg
- file with differences in the option fields. The corresponding defconfig
- files were auto-generated when switching to Kconfig. Now we have too many
- defconfig files compared with the number of the supported boards. It is
+* In the pre-Kconfig, a single board had multiple entries in the boards.cfg
+ file with differences in the option fields. The corresponding defconfig
+ files were auto-generated when switching to Kconfig. Now we have too many
+ defconfig files compared with the number of the supported boards. It is
recommended to have only one defconfig per board and allow users to select
the config options.
-- Move the config macros in header files to Kconfig. When we move at least
+* Move the config macros in header files to Kconfig. When we move at least
macros used in makefiles, we can drop include/autoconfig.mk, which makes
the build scripts much simpler.
projects / u-boot.git / commitdiff