In LogiCORE HDMI, why is the output always 12 bits per pixel in YUV 422 (YCrCb 4:2:2) mode?
According to the HDMI 1.4b and later specification, YUV422 (YCrCb 4:2:2) should always be 12-bits.
However it does allow for the use of fewer bits. If fewer than 12-bits are used, the data is still sent in 12-bit format, but just padded on the LSBs.
See the HDMI 1.4b Specification Section 6.5.1 Pixel Encodings for more details.