123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158 |
- Kconfig in U-Boot
- =================
- This document describes the configuration infrastructure of 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.
- Difference from Linux's Kconfig
- -------------------------------
- Here are some worth-mentioning configuration targets.
- - 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 a symbolic link "arch/${ARCH}/include/asm/arch" pointing to
- the SoC/CPU specific header directory
- * create include/config.h
- * create include/autoconf.mk
- * create spl/include/autoconf.mk (SPL and TPL only)
- * 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
- above would be removed.
- - defconfig
- In U-Boot, "make defconfig" is a shorthand of "make sandbox_defconfig"
- - <board>_defconfig
- Now it works as in Linux.
- The prefixes such as "+S:" in *_defconfig are deprecated.
- You can simply remove the prefixes. Do not add them for new boards.
- - <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
- --------------------------
- Prior to Kconfig, the C preprocessor based board configuration had been used
- in U-Boot.
- Although Kconfig was introduced and some configs have been moved to Kconfig,
- many of configs are still defined in C header files. It will take a very
- long term to move all of them to Kconfig. In the interim, the two different
- configuration infrastructures should coexist.
- The configuration files are generated by both Kconfig and the old preprocessor
- based configuration as follows:
- Configuration files for use in C sources
- - include/generated/autoconf.h (generated by Kconfig for Normal)
- - include/configs/<board>.h (exists for all boards)
- Configuration file for use in makefiles
- - include/config/auto.conf (generated by Kconfig)
- - include/autoconf.mk (generated by the old config for Normal)
- - spl/include/autoconfig.mk (generated by the old config for SPL)
- - tpl/include/autoconfig.mk (generated by the old config for TPL)
- 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)
- Options -> CONFIG_SYS_EXTRA_OPTIONS defined by Kconfig
- Maintainers -> "M:" entry of MAINTAINERS
- 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
- 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
- TODO
- ----
- - The option field of boards.cfg, which was used for the pre-Kconfig
- configuration, moved to CONFIG_SYS_EXTRA_OPTIONS verbatim now.
- Board maintainers are expected to implement proper Kconfig options
- and switch over to them. Eventually CONFIG_SYS_EXTRA_OPTIONS will go away.
- CONFIG_SYS_EXTRA_OPTIONS should not be used for new boards.
- - 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
- macros used in makefiles, we can drop include/autoconfig.mk, which makes
- the build scripts much simpler.
|