bus dma: a flag/quirk for page zero

Andriy Gapon avg at FreeBSD.org
Tue Jan 10 22:28:16 UTC 2012

on 11/01/2012 00:23 Matthew Jacob said the following:
>>> At the very least, require bounce buffers.
>> Not sure if I got this suggestion in this terse form.
>> Could you please explain?
> Physical address zero can be DMA'd, but via bounce buffers.
> bcopy from address zero up through a pagesize to a bounce buffer, do the dma
> from there (read case), write case the opposite order

Ah, right.  I think that that's what the patch tries to do (among other things)
if the flag is set.

Andriy Gapon

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