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author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2016-11-11 00:10:05 -0500 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2016-11-16 09:26:33 +0100 |
commit | 237e3ad0f195d8fd34f1299e45f04793832a16fc (patch) | |
tree | 3c3a7fd7442cf28789ed878c918ed018701c343d /Documentation/kbuild | |
parent | 4b7e9cf9c84b09adc428e0433cd376b91f9c52a7 (diff) | |
download | linux-237e3ad0f195d8fd34f1299e45f04793832a16fc.tar.gz linux-237e3ad0f195d8fd34f1299e45f04793832a16fc.tar.bz2 linux-237e3ad0f195d8fd34f1299e45f04793832a16fc.zip |
Kconfig: Introduce the "imply" keyword
The "imply" keyword is a weak version of "select" where the target
config symbol can still be turned off, avoiding those pitfalls that come
with the "select" keyword.
This is useful e.g. with multiple drivers that want to indicate their
ability to hook into a secondary subsystem while allowing the user to
configure that subsystem out without also having to unset these drivers.
Currently, the same effect can almost be achieved with:
config DRIVER_A
tristate
config DRIVER_B
tristate
config DRIVER_C
tristate
config DRIVER_D
tristate
[...]
config SUBSYSTEM_X
tristate
default DRIVER_A || DRIVER_B || DRIVER_C || DRIVER_D || [...]
This is unwieldy to maintain especially with a large number of drivers.
Furthermore, there is no easy way to restrict the choice for SUBSYSTEM_X
to y or n, excluding m, when some drivers are built-in. The "select"
keyword allows for excluding m, but it excludes n as well. Hence
this "imply" keyword. The above becomes:
config DRIVER_A
tristate
imply SUBSYSTEM_X
config DRIVER_B
tristate
imply SUBSYSTEM_X
[...]
config SUBSYSTEM_X
tristate
This is much cleaner, and way more flexible than "select". SUBSYSTEM_X
can still be configured out, and it can be set as a module when none of
the drivers are configured in or all of them are modular.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-2-git-send-email-nicolas.pitre@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'Documentation/kbuild')
-rw-r--r-- | Documentation/kbuild/kconfig-language.txt | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt index 069fcb3eef6e..262722d8867b 100644 --- a/Documentation/kbuild/kconfig-language.txt +++ b/Documentation/kbuild/kconfig-language.txt @@ -113,6 +113,34 @@ applicable everywhere (see syntax). That will limit the usefulness but on the other hand avoid the illegal configurations all over. +- weak reverse dependencies: "imply" <symbol> ["if" <expr>] + This is similar to "select" as it enforces a lower limit on another + symbol except that the "implied" symbol's value may still be set to n + from a direct dependency or with a visible prompt. + + Given the following example: + + config FOO + tristate + imply BAZ + + config BAZ + tristate + depends on BAR + + The following values are possible: + + FOO BAR BAZ's default choice for BAZ + --- --- ------------- -------------- + n y n N/m/y + m y m M/y/n + y y y Y/n + y n * N + + This is useful e.g. with multiple drivers that want to indicate their + ability to hook into a secondary subsystem while allowing the user to + configure that subsystem out without also having to unset these drivers. + - limiting menu display: "visible if" <expr> This attribute is only applicable to menu blocks, if the condition is false, the menu block is not displayed to the user (the symbols @@ -481,6 +509,7 @@ historical issues resolved through these different solutions. b) Match dependency semantics: b1) Swap all "select FOO" to "depends on FOO" or, b2) Swap all "depends on FOO" to "select FOO" + c) Consider the use of "imply" instead of "select" The resolution to a) can be tested with the sample Kconfig file Documentation/kbuild/Kconfig.recursion-issue-01 through the removal |