GMSL2 should use 100nF AC coupling capacitors when operating in either 3Gbps or 6Gbps modes. The GMSL2 hardware design guide says these should be 220nF when operating in GMSL1 mode. Hence, if the link is GMSL2 use 100nF. If the link is GMSL1, use 220nF; but, some customers don't know at the time of their design if the link is destined to be either GMSL1 or GMSL2. Therefore, use 220nF AC coupling capacitors to cover either operating mode. This detail just isn't clear in the hardware design guide.