Can you try reverting revision 1.15 (1.14.8.1 on netbsd-6):
revision 1.14.8.1
date: 2012-04-06 21:28:04 +0400; author: riz; state: Exp; lines: +2 -7;
Pull up following revision(s) (requested by tsutsui in ticket #160):
sys/arch/landisk/landisk/bus_dma.c: revision 1.15
Don't call sh_dcache_inv_range() on BUS_DMASYNC_POSTREAD ops
as other mips and arm ports.
All cached data is cared on BUS_DMASYNC_PREREAD and
invalidating cache without writeback could cause unexpected
data loss if specified sync region is not cacheline aligned.
This may fix "ffs_alloccg: map corrupted" panic on acardide IDE disks,
which didn't happen on USB HDD.