From owner-freebsd-hackers  Thu Nov 29 13:34:19 2001
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Date: Thu, 29 Nov 2001 15:34:15 -0600 (CST)
From: mark tinguely <tinguely@web.cs.ndsu.nodak.edu>
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To: freebsd-hackers@FreeBSD.ORG, zzhang@cs.binghamton.edu
Subject: Re: contiguous memory of a buffer
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> I am wondering whether we need contiguous memory for a PHYSICAL buffer to
> perform the DMA I/O.

yes. The DMA request should either not cross a physical page or
if the request does cross a physical page, those pages must be
contiguous.

the exception to this is if your DMA card has a memory management
unit, and you are sharing the same virtual to physical map with the
MMU and the host memory allocation space (for a driver, the kernel
physical map).

--mark tinguely.

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