is it possible to use single IOCTL to setup media pipeline?

["Zhang, Ning A" <ning.a.zhang@intel.com>]

Hello everyone

when we need to setup media pipeline, eg, for camera capture, media-ctl 
needs to be called multiple time to setup media link and subdev
formats, or similar code in a single application. this will use
multiple IOCTLs on "/dev/mediaX" and "/dev/v4l2-subdevY".

to setup media pipeline in userspace requires to fully understanding
the topology of the media stack. but the fact is only media driver
developer could know how to setup media pipeline. each time driver
updates, this would break userspace application if application
engineers don't know this change. In this case, if a IOCTL is designed
to setup media pipeline, no need to update applications, after driver
is updated.

this will not only benefit for design a single IOCTL, this also helps
to hide the detail of media pipeline, by load a binary blob which holds
information about how to setup pipeline, or hide it in bootloader/ACPI
tables/device tree, etc.

another benefit is save time for setup media pipeline, if there is a
PKI like "time for open camera". as my test, this will saves hundreds
of milliseconds.

is this acceptable?

BR.
Ning.