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: 7b34be71 ("[media] use IS_ENABLED() macro")
See-also: c5dec9fb ("V4L/DVB (4751): Fix DBV_FE_CUSTOMISE for card drivers compiled into kernel")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>

There are several left overs with my old email address.
Remove their occurrences and add myself at CREDITS, to
allow people to be able to reach me on my new addresses.
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

Instead of checking everywhere there for 3 symbols, use instead
IS_ENABLED macro.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

Raise the DVB frontends one level up, as the intention is to remove
the drivers/media/dvb directory.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

On our tests with Leadership ISDBT, the s921 frontend were not work. As its
design contained some weird things, it ended to be easier to just re-write
it, getting another frontend as an example (cx24123).

As the old s921 driver weren't used, there's no regression. Some info from
the old frontend were used as a way to double check the behavior that were
noticed on the USB dumps retrieved from Leadership driver.
Signed-off-by: NDouglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>