Hi Masahiro, On Sun, 19 Feb 2023 at 14:55, Simon Glass <s...@chromium.org> wrote: > > In the case of Linux, only one build is produced so there is only a > single configuration. For other projects, such as U-Boot and Zephyr, the > same code is used to produce multiple builds, each with related (but > different) options enabled. > > This can be handled with the existing kconfig language, but it is quite > verbose, somewhat tedious and very error-prone, since there is a lot of > duplication. The result is hard to maintain. > > Describe an extension to the Kconfig language to support easier handling > of this use case. > > Signed-off-by: Simon Glass <s...@chromium.org> > --- > > Documentation/kbuild/kconfig-language.rst | 134 ++++++++++++++++++++++ > 1 file changed, 134 insertions(+) >
Do you have any comments on this, please? Regards, Simon > diff --git a/Documentation/kbuild/kconfig-language.rst > b/Documentation/kbuild/kconfig-language.rst > index 858ed5d80defe..73fb016a5533f 100644 > --- a/Documentation/kbuild/kconfig-language.rst > +++ b/Documentation/kbuild/kconfig-language.rst > @@ -228,6 +228,24 @@ applicable everywhere (see syntax). > enables the third modular state for all config symbols. > At most one symbol may have the "modules" option set. > > +- phase declaration: "defphase" > + This defines a new build phase. See `Build Phases`_. > + > +- default phase: "phasedefault" > + This indicates the default build phase. See `Build Phases`_. > + > +- add entries for phases: "addphases" > + This creates new phase-specific entries based on a template entry and adds > + the same attributes to it. See `Build Phases`_. > + > +- set entries for phases: "setphases" > + This sets the phases which need an entry. This allows creating an entry > that > + only has a primary phase. See `Build Phases`_. > + > +- indicate a phase-specific attribute: "forphases" > + This marks an attribute as being applicable only to a particular phase or > + group of phases. See `Build Phases`_. > + > Menu dependencies > ----------------- > > @@ -319,6 +337,119 @@ MODVERSIONS directly depends on MODULES, this means > it's only visible if > MODULES is different from 'n'. The comment on the other hand is only > visible when MODULES is set to 'n'. > > +Build Phases > +------------ > + > +Some projects use Kconfig to control multiple build phases, each phase > +resulting in a separate set of object files and executable. This is the > +case in U-Boot [12]_. Zephyr OS seems to be heading this way too [13]_. > + > +Generally the phases are related, so that enabling an entry in the primary > +phase also enables it by default in the others. But in some cases it may > +be desirable to use separate conditions for each phase. > + > +All phases have a phase name, for example `SPL`. This name is used as a > +prefix to each entry used in that phase, with an underscore in between. > +So if FOO is the primary entry, the equivalent entry for the SPL phase > +is SPL_FOO. The primary phase is marked with a "phasedefault" entry. > + > +Phases are declared like any other menu entry except that also have a > +"defphase" keyword. Phase entries are normally hidden so do not have a > +prompt:: > + > + config PPL > + bool > + defphase "Primary Program Loader" > + phasedefault > + help > + This is the primary bootloader. > + > + config SPL > + bool > + defphase "Secondary Program Loader" > + help > + This is used to set up memory and load the primary bootloader. > + > +The default phase (here PPL) is assumed for all entries, in the sense that > +all entries are present in PPL by default and no prefix is needed on these > +entries. So FOO means that it applies to PPL. There must be exactly one > +default phase. > + > +The resulting menu entries can be used normally throughout the Kconfig. With > +this technique, the different build phases can be fully and individually > +controlled from Kconfig. > + > +However it is not ideal. Often the secondary phases have far fewer entries > than > +the primary phase, since they offer fewer features. Even so, each FOO that is > +needed in a phase must have an SPL_FOO, etc. To avoid an explosion of > entries, > +it is possible to indicate which are enabled, as a shortcut for creating new > +entries:: > + > + config FOO > + bool "Enable foo feature" > + addphases SPL > + depends on %BAR > + depends on QUX > + forphases SPL depends on FIZZ > + > +Note that "%" expands to the phase, so this is equivalent to (ignoring BAR):: > + > + config FOO > + bool "Enable foo feature" > + depends on BAR > + depends on QUX > + > + config SPL_FOO # Phase is prepended > + bool "Enable foo feature (SPL)" # Suffix is added > + depends on SPL_BAR # "%" dependency is expanded > + depends on QUX > + depends on FIZZ # Added only for SPL > + depends on SPL # Added automatically > + > +Attributes declared in the primary symbol FOO (such as "depends on BAR") also > +apply to the secondary ones. > + > +An entry without any 'addphases' attribute applies to all phases. Individual > +phase entries are not available in that case. If the entry is enabled, then > +it is enabled for all phases. Only one entry appears in the resulting > Kconfig. > + > +In the case where an entry should apply only to the primary phase (or a > +particular set of phases), you can uses "setphases" instead of "addphases":: > + > + config FOO > + bool "Enable foo feature" > + setphases PPL > + > +This means that even if the option is enabled, it will not be active outside > +the primary-phase build, here named "PPL". > + > +Internally, phases are implemented simply by creating new entries. These > +appear in the Kconfig as per normal. It would be possible for a Kconfig > +editor to show the entries just for a particular phase, leaving out the > +entries not applicable to that phase. > + > +When phases are used, the Kconfig tool outputs separate auto.conf files for > +each phase (e.g. auto_spl.conf), so that if SPL_FOO is enabled, then > +`CONFIG_FOO=y` is present in the file. This makes it easy for the build > system > +to build the correct code, use IS_ENABLED(), etc. > + > +To ensure that the correct options are enabled for each build, in addition to > +the normal CONFIG_FOO option in the file, phase symbols are added too. For > +example, if FOO is enabled in the SPL phase, then auto_spl.conf contains:: > + > + CONFIG_FOO=y > + CONFIG_SPL_FOO=y > + > +The phase-specific line (CONFIG_SPL_FOO) is seldom needed, but it allows one > +phase to access the symbols from another phase. For example, if the primary > +phase needs to receive boot timings from SPL, then support for boot timings > must > +be added in both phases. If the timings are at a fixed address, this can be > in a > +shared symbol (like CONFIG_SPL_TIMING_BASE) that both phases can access. > + > +Technical note: the grammar definition of <symbol> in this documeent does not > +include the "%" prefix at present. It can be used with any attribute. It > cannot > +be used with any top-level items, like "config", "menuconfig", "if" and > "menu". > + > > Kconfig syntax > -------------- > @@ -744,3 +875,6 @@ https://kernelnewbies.org/KernelProjects/kconfig-sat > .. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf > .. [10] https://paulgazzillo.com/papers/esecfse21.pdf > .. [11] https://github.com/paulgazz/kmax > + > +.. [12] https://u-boot.readthedocs.io/en/latest/develop/spl.html > +.. [13] https://docs.zephyrproject.org/latest/build/sysbuild/index.html > -- > 2.39.2.637.g21b0678d19-goog >