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Subject: Re: dma
To: AlexHully <deco33000@yandex.com>, freebsd-hackers@freebsd.org
References: <298361446978177@web22g.yandex.ru>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <563F38DD.5070409@selasky.org>
Date: Sun, 8 Nov 2015 12:58:21 +0100
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On 11/08/15 11:22, AlexHully wrote:
> Hi,
>
> I would like a clarification for dma.
>
> The context: most dma capable devices have 32 bits address range.
> Is it correct that, if there was no 3G/1G mapping in the kernel, or that kernel low memory could map 4Gb memory, one could choose any free addresses in that low memory to set up a dma buffer?
>
> That would avoid all the mapping hassle, and performance cost associated.
>

I've seen USB controllers only supporting 2G address range.

--HPS