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Date:      Wed, 11 Jan 2012 00:28:08 +0200
From:      Andriy Gapon <avg@FreeBSD.org>
To:        mj@feral.com
Cc:        FreeBSD current <freebsd-current@FreeBSD.org>
Subject:   Re: bus dma: a flag/quirk for page zero
Message-ID:  <4F0CBB78.502@FreeBSD.org>
In-Reply-To: <alpine.BSF.2.00.1201101422380.92131@ns1.feral.com>
References:  <4F0C9D14.60705@FreeBSD.org> <alpine.BSF.2.00.1201101252530.86261@ns1.feral.com> <4F0CAD03.1090605@FreeBSD.org> <alpine.BSF.2.00.1201101422380.92131@ns1.feral.com>

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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



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