How does the invisible kernel configuration item 'VIDEO_DEV' set the value 'm' while its default value is 'y'?

[孙滢]

Hi,
VIDEO_DEV is defined in Kconfig as follows:

menu	"Media core support"
	visible	if	!	MEDIA_SUPPORT_FILTER
config	VIDEO_DEV
	tristate	"Video4Linux core"
	default	MEDIA_CAMERA_SUPPORT	||	MEDIA_ANALOG_TV_SUPPORT	||	MEDIA_RADIO_SUPPORT	||	MEDIA_SDR_SUPPORT	||	MEDIA_PLATFORM_SUPPORT	||	MEDIA_TEST_SUPPORT
	depends	on	(	I2C	||	I2C	=	n	)
	select	RATIONAL
	select	VIDEOBUF2_V4L2	if	VIDEOBUF2_CORE
	help
		Enables the V4L2 API, used by cameras, analog TV, video grabbers,
		radio devices and by some input devices.


In Ubuntu, MEDIA_SUPPORT_FILTER = y, So VIDEO_DEV is not visible and cannot be set in menuconfig. 
Only the default value can be used, and the default value calculated in Kconfig grammar is 'y'.
But the actual Ubuntu value is 'm'.

How can I change the value of VIDEO_DEV to 'm'? Is it changed by setting VIDEO_DEV=m in the config file of the local build environment?


Thanks!