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[media] Add and use IS_REACHABLE macro

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In the media drivers, the v4l2 core knows about all submodules
and calls into them from a common function. However this cannot
work if the modules that get called are loadable and the
core is built-in. In that case we get

drivers/built-in.o: In function `set_type':
drivers/media/v4l2-core/tuner-core.c:301: undefined reference to `tea5767_attach'
drivers/media/v4l2-core/tuner-core.c:307: undefined reference to `tea5761_attach'
drivers/media/v4l2-core/tuner-core.c:349: undefined reference to `tda9887_attach'
drivers/media/v4l2-core/tuner-core.c:405: undefined reference to `xc4000_attach'

This was working previously, until the IS_ENABLED() macro was used
to replace the construct like

 #if defined(CONFIG_DVB_CX24110) || (defined(CONFIG_DVB_CX24110_MODULE) && defined(MODULE))

with the difference that the new code no longer checks whether it is being
built as a loadable module itself.

To fix this, this new patch adds an 'IS_REACHABLE' macro, which evaluates
true in exactly the condition that was used previously. The downside
of this is that this trades an obvious link error for a more subtle
runtime failure, but it is clear that the change that introduced the
link error was unintentional and it seems better to revert it for
now. Also, a similar change was originally created by Trent Piepho
and then reverted by teh change to the IS_ENABLED macro.

Ideally Kconfig would be used to avoid the case of a broken dependency,
or the code restructured in a way to turn around the dependency, but either
way would require much larger changes here.

Fixes: 7b34be71db ("[media] use IS_ENABLED() macro")
See-also: c5dec9fb24 ("V4L/DVB (4751): Fix DBV_FE_CUSTOMISE for card drivers compiled into kernel")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Arnd Bergmann
2015-02-18 14:12:42 -03:00
committed by Mauro Carvalho Chehab
parent a87a4d3428
commit 9b174527e7
116 changed files with 125 additions and 116 deletions
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9
include/linux/kconfig.h
View File

@@ -43,4 +43,13 @@
*/
#define IS_MODULE(option) config_enabled(option##_MODULE)
/*
* IS_REACHABLE(CONFIG_FOO) evaluates to 1 if the currently compiled
* code can call a function defined in code compiled based on CONFIG_FOO.
* This is similar to IS_ENABLED(), but returns false when invoked from
* built-in code when CONFIG_FOO is set to 'm'.
*/
#define IS_REACHABLE(option) (config_enabled(option) || \
(config_enabled(option##_MODULE) && config_enabled(MODULE)))
#endif /* __LINUX_KCONFIG_H */