dummy/linux-stable-mirror
1
0
Fork 1
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2025-04-19 20:58:31 +09:00
Code Issues Packages Projects Releases Wiki Activity

docs: kconfig: Mention IS_REACHABLE as way for optional dependency

Browse Source 
Several drivers express optional Kconfig dependency with FOO || !FOO,
but for many choices this is not suitable: lack of stubs for !FOO
like in HWMON.  Describe the second, less favorable way of optional
dependency with IS_REACHABLE by moving the code from "imply" chapter to
"Optional dependencies".

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Krzysztof Kozlowski 2025-02-17 12:31:53 +01:00 committed by Masahiro Yamada
parent d0beb73d1d
commit 700bd25bd4
1 changed files with 18 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
Documentation/kbuild/kconfig-language.rst
View File

@ -194,16 +194,6 @@ applicable everywhere (see syntax).
ability to hook into a secondary subsystem while allowing the user to
configure that subsystem out without also having to unset these drivers.
Note: If the combination of FOO=y and BAZ=m causes a link error,
you can guard the function call with IS_REACHABLE()::
foo_init()
{
if (IS_REACHABLE(CONFIG_BAZ))
baz_register(&foo);
...
}
Note: If the feature provided by BAZ is highly desirable for FOO,
FOO should imply not only BAZ, but also its dependency BAR::
@ -588,7 +578,9 @@ uses the slightly counterintuitive::
depends on BAR || !BAR
This means that there is either a dependency on BAR that disallows
the combination of FOO=y with BAR=m, or BAR is completely disabled.
the combination of FOO=y with BAR=m, or BAR is completely disabled. The BAR
module must provide all the stubs for !BAR case.
For a more formalized approach if there are multiple drivers that have
the same dependency, a helper symbol can be used, like::
@ -599,6 +591,21 @@ the same dependency, a helper symbol can be used, like::
config BAR_OPTIONAL
def_tristate BAR || !BAR
Much less favorable way to express optional dependency is IS_REACHABLE() within
the module code, useful for example when the module BAR does not provide
!BAR stubs::
foo_init()
{
if (IS_REACHABLE(CONFIG_BAR))
bar_register(&foo);
...
}
IS_REACHABLE() is generally discouraged, because the code will be silently
discarded, when CONFIG_BAR=m and this code is built-in. This is not what users
usually expect when enabling BAR as module.
Kconfig recursive dependency limitations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~