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Date: Wed, 11 Jan 2012 00:28:08 +0200
From: Andriy Gapon <avg@FreeBSD.org>
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Cc: FreeBSD current <freebsd-current@FreeBSD.org>
Subject: Re: bus dma: a flag/quirk for page zero
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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