As we understand, instead of negotiating at 256 bytes, the Xilinx* NIC card on the Intel® Server Board S2600CP does at just 128 bytes. If we infer correctly, although the BIOS of the Intel® Server Board S2600CP does not feature an option to manually alter MPS settings, based on the fact no Xilinx card is listed among the officially validated hardware (click here for the complete list), we recommend the following:
1. Set the PCI Configuration/Memory Mapped IO Size BIOS option to Auto; save, reboot and test. If the situation still continues, try forcing it to 256:
2. Test with the BIOS default settings if the Xilinx still does not negotiate at 256b.
3. Ensure the BIOS/firmware of your Intel® Server Board S2600CP is at the latest (click here); otherwise, please, check with the NIC card manufacturer.