From owner-freebsd-scsi@FreeBSD.ORG  Mon Jun  9 18:34:26 2008
Return-Path: <owner-freebsd-scsi@FreeBSD.ORG>
Delivered-To: freebsd-scsi@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 78FAC1065671
	for <freebsd-scsi@freebsd.org>; Mon,  9 Jun 2008 18:34:26 +0000 (UTC)
	(envelope-from weimin.pan@hp.com)
Received: from g5t0008.atlanta.hp.com (g5t0008.atlanta.hp.com [15.192.0.45])
	by mx1.freebsd.org (Postfix) with ESMTP id 4EAB08FC1A
	for <freebsd-scsi@freebsd.org>; Mon,  9 Jun 2008 18:34:26 +0000 (UTC)
	(envelope-from weimin.pan@hp.com)
Received: from G1W0401.americas.hpqcorp.net (g1w0401.americas.hpqcorp.net
	[16.236.31.6]) (using TLSv1 with cipher RC4-MD5 (128/128 bits))
	(No client certificate requested)
	by g5t0008.atlanta.hp.com (Postfix) with ESMTP id DA8B024A48
	for <freebsd-scsi@freebsd.org>; Mon,  9 Jun 2008 18:18:28 +0000 (UTC)
Received: from G1W0397.americas.hpqcorp.net (16.236.31.21) by
	G1W0401.americas.hpqcorp.net (16.236.31.6) with Microsoft SMTP Server
	(TLS) id 8.1.263.0; Mon, 9 Jun 2008 18:18:16 +0000
Received: from G1W0491.americas.hpqcorp.net ([16.236.84.125]) by
	G1W0397.americas.hpqcorp.net ([16.236.31.21]) with mapi; Mon, 9 Jun 2008
	18:18:16 +0000
From: "Pan, Weimin" <weimin.pan@hp.com>
To: "freebsd-scsi@freebsd.org" <freebsd-scsi@freebsd.org>
Date: Mon, 9 Jun 2008 18:18:16 +0000
Thread-Topic: How to directly pass a dma physical address and length from
	SCSI upper layer to LLD without mapping the dma memory to kernel pages
Thread-Index: AcjKXTAITt/dfm2bQ8aDKjYW2aDIBQ==
Message-ID: <6B24EEDBA38D764293B27C04FE414CC64E40604C07@G1W0491.americas.hpqcorp.net>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
acceptlanguage: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Cc: "Pan, Weimin" <weimin.pan@hp.com>
Subject: How to directly pass a dma physical address and length from SCSI
 upper layer to LLD without mapping the dma memory to kernel pages
X-BeenThere: freebsd-scsi@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: SCSI subsystem <freebsd-scsi.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-scsi>,
	<mailto:freebsd-scsi-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-scsi>
List-Post: <mailto:freebsd-scsi@freebsd.org>
List-Help: <mailto:freebsd-scsi-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-scsi>,
	<mailto:freebsd-scsi-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 09 Jun 2008 18:34:26 -0000

SCSI upper layer can pass a scatterlist to middle layer and LLD. Normally t=
he page_link, length, and offset is set in the scatterlist. LLD will conver=
t to dma_address from pages by itself. That means the dma physical address =
has to map to kernel memory space before it can be passed to LLD for data t=
ransfer. If I have a large dma memroy and it doesn't need to be touched by =
kernel or user mode Apps, it is a performance penalty to force to do that.

Is there a way to directly pass a dma physical address from upper layer to =
LLD (like use dma_address in a scatterlist)?
I looked at a couple of LLD drivers and none of them handle this kind of si=
tuation.