Aurélien Zanelli authored Oct 01, 2015 and Nicolas Dufresne committed Mar 24, 2016

A device can support more than one colorspace for a given image
dimension and pixel format. So we have to probe all the supported
colorspace and not only rely on the default one. Otherwise we could end
up with negotiation failure if the caps colorimetry field don't match
the v4l2 device default one even if the v4l2 could support such
colorimetry.

This patch enable probing if colorspace for both capture and output
device. It really makes sense for output device since the colorspace
shall be set by the application and a little less for capture device
which, at the moment, shall provide the colorspace; ie: the v4l2
specification seems to not take into account the fact that a capture
device could do colorspace conversion.

As a side effet, probing takes some times and so sligthly delay v4l2
initialization. Note that this patch only probe colorspace and not all
colorspace, matrix, transfer and range combination to avoid taking too
much time, especially with low-speed devices as full probing do 1782
ioctl.

https://bugzilla.gnome.org/show_bug.cgi?id=755937