Fixed in kernel 4.11.3, I believe:
1)
MB: ASRock x370 Taichi
BIOS: UEFI 2.30
RAM: Crucial CT2K16G4WFD824A 32GB (2 x 16GB ECC, 2400MHz, Dual Rank)
Banks: a2, b2
2)root@deepthought:~# dmesg | grep 'edac\|EDAC\|Linux version'
[ 0.000000] Linux version 4.11.3 (marc@deepthought) (gcc version 7.1.0 (GCC) ) #1 SMP Fri May 26 11:21:15 BST 2017
[ 8.811227] EDAC MC: Ver: 3.0.0
[ 8.822946] EDAC amd64: Node 0: DRAM ECC enabled.
[ 8.824590] EDAC amd64: F17h detected (node 0).
[ 8.825479] EDAC MC: UMC0 chip selects:
[ 8.825481] EDAC amd64: MC: 0: 0MB 1: 0MB
[ 8.827314] EDAC amd64: MC: 2: 16383MB 3: 16383MB
[ 8.828115] EDAC amd64: MC: 4: 0MB 5: 0MB
[ 8.828889] EDAC amd64: MC: 6: 0MB 7: 0MB
[ 8.829685] EDAC MC: UMC1 chip selects:
[ 8.829686] EDAC amd64: MC: 0: 0MB 1: 0MB
[ 8.830658] EDAC amd64: MC: 2: 16383MB 3: 16383MB
[ 8.831514] EDAC amd64: MC: 4: 0MB 5: 0MB
[ 8.832092] EDAC amd64: MC: 6: 0MB 7: 0MB
[ 8.832749] EDAC amd64: using x8 syndromes.
[ 8.833485] EDAC amd64: MCT channel count: 2
[ 8.834253] EDAC MC0: Giving out device to module amd64_edac controller F17h: DEV 0000:00:18.3 (INTERRUPT)
[ 8.835695] EDAC PCI0: Giving out device to module amd64_edac controller EDAC PCI controller: DEV 0000:00:18.0 (POLLED)
[ 8.836301] AMD64 EDAC driver v3.5.0