From owner-freebsd-arch@FreeBSD.ORG  Mon Jun 30 07:03:57 2003
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 4862C37B404
	for <freebsd-arch@freebsd.org>; Mon, 30 Jun 2003 07:03:57 -0700 (PDT)
Received: from duke.cs.duke.edu (duke.cs.duke.edu [152.3.140.1])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 1AB4643FBD
	for <freebsd-arch@freebsd.org>; Mon, 30 Jun 2003 07:03:56 -0700 (PDT)
	(envelope-from gallatin@cs.duke.edu)
Received: from grasshopper.cs.duke.edu (grasshopper.cs.duke.edu
	[152.3.145.30])
	by duke.cs.duke.edu (8.12.9/8.12.9) with ESMTP id h5UE3qwV002660
	(version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO);
	Mon, 30 Jun 2003 10:03:52 -0400 (EDT)
Received: (from gallatin@localhost)
	by grasshopper.cs.duke.edu (8.11.6/8.9.1) id h5UE3lh08442;
	Mon, 30 Jun 2003 10:03:47 -0400 (EDT)
	(envelope-from gallatin@cs.duke.edu)
From: Andrew Gallatin <gallatin@cs.duke.edu>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Message-ID: <16128.17218.973911.980939@grasshopper.cs.duke.edu>
Date: Mon, 30 Jun 2003 10:03:46 -0400 (EDT)
To: Terry Lambert <tlambert2@mindspring.com>
In-Reply-To: <3EFD4755.49BAF150@mindspring.com>
References: <3EF3C12F.9060303@btc.adaptec.com>
	<16124.39930.142492.356163@grasshopper.cs.duke.edu>
	<3EFC9F2D.6020908@btc.adaptec.com>
	<16124.43999.333761.397624@grasshopper.cs.duke.edu>
	<3EFCAC7A.6060305@btc.adaptec.com>
	<16124.45051.919899.414795@grasshopper.cs.duke.edu>
	<3EFD4755.49BAF150@mindspring.com>
X-Mailer: VM 6.75 under 21.1 (patch 12) "Channel Islands" XEmacs Lucid
cc: Scott Long <scott_long@btc.adaptec.com>
cc: Andrew Gallatin <gallatin@cs.duke.edu>
cc: freebsd-arch@freebsd.org
Subject: Re: API change for bus_dma
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussion related to FreeBSD architecture
	<freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 30 Jun 2003 14:03:57 -0000


Terry Lambert writes:
 > Andrew Gallatin wrote:
 > > Most sparc's have 2 different sorts of DMA modes.  One is cache
 > > coherent (aka DDI_DMA_CONSISTENT) -- this is what we all know and love
 > > from PC, alphas, macs, etc.
 > 
 > "contiguous"
 > 
 > 
 > > The other mode (DDI_DMA_STREAMING) allows non cache coherent DMA.
 > > This requires you to call ddi_dma_sync() between your last touch of
 > > the data and you starting a DMA read from a device.  And vice-versa
 > > for a DMA write.
 > 
 > "scatter/gather"
 > 
 > > The reason people use DDI_DMA_STREAMING is because coherent DMA
 > > bandwith tends to be abysmal on most sparcs.
 > 


The idea is that I want to establish a mapping that can be used many
times without any driver or kernel attention.  I don't want to do
anything in terms of a system call, or interrupt, etc, to sync the
cache with the state of the DMA'ed page before a DMA read or after a DMA
write.

For example, scatter gather mapping on alphas (if FreeBSD supported it
for PCI devices) would be fine with me since its cache-coherent and
doesn't require any ddi_dma_sync() operations.


Drew