media: em28xx: split up em28xx_dvb_init to reduce stack size

With CONFIG_KASAN, the init function uses a large amount of kernel stack:

drivers/media/usb/em28xx/em28xx-dvb.c: In function 'em28xx_dvb_init.part.4':
drivers/media/usb/em28xx/em28xx-dvb.c:2061:1: error: the frame size of 3232 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

Using gcc-7 with -fsanitize-address-use-after-scope makes this even worse:

drivers/media/usb/em28xx/em28xx-dvb.c: In function 'em28xx_dvb_init':
drivers/media/usb/em28xx/em28xx-dvb.c:2069:1: error: the frame size of 4280 bytes is larger than 3072 bytes [-Werror=frame-larger-than=]

By splitting out each part of the switch/case statement that has its own local
variables into a separate function, no single one of them uses more than 500 bytes,
and with a noinline_for_stack annotation we can ensure that they are not merged
back together.

[mchehab@s-opensource.com: fix conflict with changeset
 be7fd3c3 ("media: em28xx: Hauppauge DualHD second tuner functionality")]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>