1)Can csi clock be over 400Mhz at 4 lane?
>> The maximum bandwidth that CX3 can support is limited by the GPIF II block of CX3. As mentioned in TRM it can support till 2.4Gbps i.e. when 100 MHz clock and 24 bit GPIF interface is used. So if you want to use all the 4 lanes, then CX3 can support only 600Mbps/lane. Else the video will not stream properly due to data loss.
As CSI clock is DDR clock you can keep the CSI clock less than 300 MHz when you are using all 4 lanes and GPIF interface is of 24 bits. If GPIF interface is of 16 bits the bandwidth will reduces further and hence need to reduce the CSI clock further.
2) CX3 MIPI Reciver Configuration default value is O.K
>> Other than the CSI clock everything else seems fine. You can modify the clock and share the settings, once again, for us to check.
3) Are there any more settings I need to add?
>> No additional settings are needed for CX3 MIPI Receiver Configuration.