The minimum CSI clock required= (H-Active (in Pixels) × Pixel Depth) ÷ H-Total (in µs) ÷2 ÷ Data Lanes
i.e. = (640 X 8) / 31.67 /2 /1 = 80.833 Mhz
Here 31.67 us is taken from Please help me understand timing of these MIPI waveforms .
In general, this value will be less than this number. Because 31.67 us includes the headers as well.
Encoding is optional in MIPI CSI-2. Error correction code (24-bit) will be part of data packetheader and 16 bit checksum in packetfooter.
You can see this in this figure.