From owner-freebsd-stable@FreeBSD.ORG  Fri Sep  5 14:05:08 2003
Return-Path: <owner-freebsd-stable@FreeBSD.ORG>
Delivered-To: freebsd-stable@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id B9BF816A4C1
	for <stable@freebsd.org>; Fri,  5 Sep 2003 14:05:08 -0700 (PDT)
Received: from fledge.watson.org (fledge.watson.org [204.156.12.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP id C71CC43F93
	for <stable@freebsd.org>; Fri,  5 Sep 2003 14:05:05 -0700 (PDT)
	(envelope-from robert@fledge.watson.org)
Received: from fledge.watson.org (localhost [127.0.0.1])
	by fledge.watson.org (8.12.9/8.12.9) with ESMTP id h85L46rO022982;
	Fri, 5 Sep 2003 17:04:06 -0400 (EDT)
	(envelope-from robert@fledge.watson.org)
Received: from localhost (robert@localhost)h85L46MZ022979;
	Fri, 5 Sep 2003 17:04:06 -0400 (EDT)
Date: Fri, 5 Sep 2003 17:04:05 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
X-Sender: robert@fledge.watson.org
To: Mike Tancsa <mike@sentex.net>
In-Reply-To: <5.2.0.9.0.20030905074316.03acc028@209.112.4.2>
Message-ID: <Pine.NEB.3.96L.1030905170225.19724G-100000@fledge.watson.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
cc: stable@freebsd.org
cc: Luoqi Chen <lchen@briontech.com>
Subject: Re: HEADS UP: ATA  bus dma code MFC'd
X-BeenThere: freebsd-stable@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Production branch of FreeBSD source code
	<freebsd-stable.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>,
	<mailto:freebsd-stable-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-stable>
List-Post: <mailto:freebsd-stable@freebsd.org>
List-Help: <mailto:freebsd-stable-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>,
	<mailto:freebsd-stable-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 05 Sep 2003 21:05:08 -0000


On Fri, 5 Sep 2003, Mike Tancsa wrote:

>          A naive question, but what does the bus DMA code do in STABLE ?

busdma abstracts the management of buffer addresses for DMA to permit
drivers to operate across hardware architectures and addressing schemes
without modification.  This is required for some drivers to support PAE,
where the size of a hardware address is not the same as an address
pointer, which was an assumption present in several drivers previously. 
It's being used in -CURRENT to improve the portability of drivers to
64-bit architectures, but the primary benefit on -STABLE is making the
drivers work with PAE. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories