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Diffstat (limited to 'roms/u-boot/doc/README.kconfig')
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diff --git a/roms/u-boot/doc/README.kconfig b/roms/u-boot/doc/README.kconfig new file mode 100644 index 000000000..0689f66c2 --- /dev/null +++ b/roms/u-boot/doc/README.kconfig @@ -0,0 +1,158 @@ +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. |