DMA clarification

[Jeffrey Zank - SBus Software]

| >You need to be clear here.  If you are using DVMA, 600 KBytes sounds about
| >right for mb_ampalloc() and mb_mapfree() type of usage.  Total space for
| >DVMA is about 1 MByte, and its shared with all other devices that do DVMA.
| >You really cannot "reconfigure" your kernel to add more space, you are
| >limited by other kernel resources that currently are not configurable
| >(PMEGS, and IOPB Memory for example).
| 
| Please post a correction - DVMA is a softwared fiction on the SBus
| machines - you can see all of the kernel context from the SBus. There
| is no 1MB DVMA window in hardware on that machine.

I have been asked to clarify this a bit more, so;

I do not refer to DVMA as being a hardware limit here.  I was attempting
to point out that under 4.1 you can *expect* to map up about 600kbytes
worth of DVMA (using mb_ampalloc()) and that the 1 MB is not configurable
by the user (without hacking up the kernel).  The 4/60 and 4/65 no longer
have  the hardware limits that forced the 1 MB limit.    You should look
at bp_mapin() for larger size mappings.