The Linux media controller framework

Media devices turn out to be very complex, involving several IP blocks of the SoC and thus requiring video stream (re)routing.

Now, let's consider a case where we have a much more sophisticated SoC made of two more on-chip sub-devices – let's say a resizer and an image converter, called baz and biz.

In the previous example in the V4L2 async section, the setup was made up of one bridge device and one sub-device (the fact that it is off-chip does not matter), the camera sensor. This was quite straightforward. Luckily, things worked. But what if now we have to route the stream through the image converter or the image resizer, or even through both IPs? Or, say we have to switch from one to the other (dynamically)?

We could achieve this either via sysfs or ioctls, but this would have the following problems:

• It would be too ugly (no doubt) and probably buggy.
• It would be too hard (a lot of work).
• It would be deeply...