Full RP1 access can be done with PCIe memory bar1

dmesg | grep rp1

[ 1.846003] rp1 0000:01:00.0: bar0 len 0x4000, start 0x1f00410000, end 0x1f00413fff, flags, 0x40200
[ 1.855094] rp1 0000:01:00.0: bar1 len 0x400000, start 0x1f00000000, end 0x1f003fffff, flags, 0x40200
[ 1.864364] rp1 0000:01:00.0: enabling device (0000 -> 0002)
[ 1.871234] rp1 0000:01:00.0: chip_id 0x20001927