The same case was already discussed here, but with no result:
Finally found that adding `swiotlb=1` to kernel args releases 64 MB of memory:
/boot/armbianEnv.txt:extraargs=... nokaslr cma=0 swiotlb=0
but not disables it completely:
[ 0.000000] software IO TLB: SWIOTLB bounce buffer size roundup to 1MB
Now:
MemTotal: 487684 kB
Alternative option `iommu=off` does not work.
So it's not for graphics.
This option looks reasonable for less than 4 GB RAM devices(?)
If someone knows potential drawbacks, please disclose.
