Are there known issues with accessing external DDR from the FPGA fabric on an Arria 10 SoC when using the Linux 4 kernel?

Hi,

Can you elaborate the specific issue? Do you mean that for both Linux 3 and 4.20, the registers in the FPGA fabric can be written and read back? or just for Linux 3?

You can try this External Memory Interfaces Intel Arria 10 FPGA IP Design Example User Guide, this might help:

https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/ug/ug-20118.pdf

Regards.