RPi4B's DMA11 (DMA4 engine example) vs. xHCI/pcie

[Mark Millard]

On 2020-Sep-30, at 14:15, Robert Crowston <crowston at protonmail.com> wrote:

> Very interesting analysis. Certainly uncovered a few things I wasn't aware of.
> 
> By default sc->sc_bus.dma_bits in xhci_init is 64 bits; I toggle it back to 32 bits in the xhci shim I wrote for the Pi 4. You can see that output in a verbose dmesg.
> 

My biggest worry from all that material, for things as they currently
are, is that it appears that FreeBSD could try to use a RPi4B DMA LITE
engine but not follow its limitations when doing so. For example,
ending up using a smaller size DMA transfer than intended (just 16 bits
for size). (Other RPi's might have the same issue?)

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)