Gentoo kernel 3.7.9 webcams, V4L, UVC, video: kernel config

For those of us adventurous enough to upgrade to the Gentoo kernel 3.7.9 using their own custom kernel config… As was the case for upgrading to the Gentoo kernel 3.6.11, beware that the config spec for the video modules and webcam modules including the USB UVC/video and V4L have changed in the config hierarchy and may well need reenabling, as listed below.

(The mainline kernel is already pretty mean and small and even clears out unneeded modules automatically at runtime, so why go to all this custom-compile stuff trouble? Normally there is no need to. However, usefully for small or low powered or ultra-secure systems, or for obscure hardware, you can be very selective in what kernel functions and features are made available. You should also see a small improvement in the boot time. Storage space and system footprint can be made smaller. As an aside, you also gain a good speedup in the time needed to compile the fewer features for a small custom kernel. Considering further: The main reason has still got to be the “tweak factor” for experimenting with obscure or experimental functionality – all very educational! 🙂 )

Lost your /dev/video0 and you have a custom config for your kernel? Check that you still have enabled the appropriate kernel modules for:

CONFIG_MEDIA_SUPPORT:

If you want to use Webcams, Video grabber devices and/or TV devices
enable this option and other options below. Additional info and docs
are available on the web at https://linuxtv.org

Symbol: MEDIA_SUPPORT [=m]
Type  : tristate 
Prompt: Multimedia support
  Defined at drivers/media/Kconfig:5
  Depends on: HAS_IOMEM [=y]
  Location:
    -> Device Drivers

CONFIG_MEDIA_CAMERA_SUPPORT:

Enable support for webcams and video grabbers.

Say Y when you have a webcam or a video capture grabber board.

Symbol: MEDIA_CAMERA_SUPPORT [=y]
Type  : boolean
Prompt: Cameras/video grabbers support
  Defined at drivers/media/Kconfig:21
  Depends on: MEDIA_SUPPORT [=m]
  Location:
    -> Device Drivers
      -> Multimedia support (MEDIA_SUPPORT [=m])

CONFIG_MEDIA_USB_SUPPORT:

Enable media drivers for USB bus.
If you have such devices, say Y.

Symbol: MEDIA_USB_SUPPORT [=y]
Type  : boolean
Prompt: Media USB Adapters
  Defined at drivers/media/usb/Kconfig:1
  Depends on: USB [=y] && MEDIA_SUPPORT [=m]
  Location:
    -> Device Drivers
      -> Multimedia support (MEDIA_SUPPORT [=m])

CONFIG_USB_VIDEO_CLASS:

Support for the USB Video Class (UVC).  Currently only video
input devices, such as webcams, are supported.
For more information see: 

Symbol: USB_VIDEO_CLASS [=m]
Type  : tristate
Prompt: USB Video Class (UVC)
  Defined at drivers/media/usb/uvc/Kconfig:1
  Depends on: MEDIA_SUPPORT [=m] && MEDIA_USB_SUPPORT [=y] && MEDIA_CAMERA_SUPPORT [=y]
  Location:
    -> Device Drivers
      -> Multimedia support (MEDIA_SUPPORT [=m]) 
        -> Media USB Adapters (MEDIA_USB_SUPPORT [=y])  
  Selects: VIDEOBUF2_VMALLOC [=n]

That is, in the kernel config, enable as appropriate in:

Device Drivers (Multimedia support)
Device Drivers -> Multimedia support
Device Drivers -> Multimedia support -> Media USB Adapters

… And compile, install and reboot.