+Masahiro Yamada <masahi...@kernel.org> On Fri, 24 Feb 2023 at 19:04, Simon Glass <s...@chromium.org> wrote:
> +lk > > 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(+) > > > > 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 > > >
