Date: Sun, 8 Nov 2015 12:58:21 +0100 From: Hans Petter Selasky <hps@selasky.org> To: AlexHully <deco33000@yandex.com>, freebsd-hackers@freebsd.org Subject: Re: dma Message-ID: <563F38DD.5070409@selasky.org> In-Reply-To: <298361446978177@web22g.yandex.ru> References: <298361446978177@web22g.yandex.ru>
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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
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