In message <199805262241.PAA10126@Cup.DSG.Stanford.EDU> Jonathan Stone writes:
: I forget the exact details for output. If writes to the DMA bnuffer
: were uncached and the writebuffer is drained, then flushes aren't
: necessary.  If there were cached writes to the DMA buffer, there may
: be some short delay necessary to let dirty cache lines drain down to
: DRAM.

I recall from the R4400 that is in my Deskstation that I needed to do
all accesses to the mailbox of the buslogic card via uncached memory,
both reads and writes.  When I tried to do it via kernel memory I had
all kinds of cache coherency problems.  I don't think you need to
flush the write buffers when you do all your accesses uncached, but it
couldn't hurt.

I don't have all the details in front of me right now, but is
definitely was annoying.

Warner