From mboxrd@z Thu Jan  1 00:00:00 1970
From: FUJITA Tomonori <tomof@acm.org>
Subject: Re: [PATCH v3 2/2][BNX2]: Add iSCSI support to BNX2 devices.
Date: Thu, 27 Sep 2007 17:06:13 +0900
Message-ID: <20070926075800T.tomof@acm.org>
References: <46F8C935.8050907@suse.de>
	<20070925133624H.tomof@acm.org>
	<46FB5C6B.3020506@garzik.org>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: tomof@acm.org, hare@suse.de, open-iscsi@googlegroups.com,
	hch@infradead.org, davem@davemloft.net, mchristi@redhat.com,
	netdev@vger.kernel.org, anilgv@broadcom.com, talm@broadcom.com,
	lusinsky@broadcom.com, uri@broadcom.com,
	fujita.tomonori@lab.ntt.co.jp, benh@kernel.crashing.org,
	jens.axboe@oracle.com, James.Bottomley@SteelEye.com,
	linux-scsi@vger.kernel.org
To: jeff@garzik.org
Return-path: <netdev-owner@vger.kernel.org>
Received: from mo11.iij4u.or.jp ([210.138.174.79]:56194 "EHLO mo11.iij4u.or.jp"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750878AbXI0IHQ (ORCPT <rfc822;netdev@vger.kernel.org>);
	Thu, 27 Sep 2007 04:07:16 -0400
In-Reply-To: <46FB5C6B.3020506@garzik.org>
Sender: netdev-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

CC'ed Jens, James, and linux-scsi.

On Thu, 27 Sep 2007 03:31:55 -0400
Jeff Garzik <jeff@garzik.org> wrote:

> FUJITA Tomonori wrote:
> > Yeah, we could nicely handle lld's restrictions (especially with
> > stacking devices). But iommu code needs only max_segment_size and
> > seg_boundary_mask, right? If so, the first simple approach to add two
> > values to device structure is not so bad, I think.
> 
> (replying to slightly older email in the thread)
> (added benh, since we've discussed this issue in the past)
> 
> dumb question, what happened to seg_boundary_mask?

I'll work on it too after finishing max_seg_size.


> If you look at drivers/ata/libata-core.c:ata_fill_sg(), you will note 
> that we split s/g segments after DMA-mapping.  Looking at libata LLDD's, 
> you will also note judicious use of ATA_DMA_BOUNDARY (0xffff).

I know the workaround since I fixed libata's sg chaining patch.


> It was drilled into my head by James and benh that I cannot rely on the 
> DMA boundary + block/scsi + dma_map_sg() to ensure that my S/G segments 
> never cross a 64K boundary, a legacy IDE requirement.  Thus the 
> additional code in ata_fill_sg() to split S/G segments straddling 64K, 
> in addition to setting dma boundary to 0xffff.

I think that the block layer can handle both max_segment_size and
seg_boundary_mask properly (and SCSI-ml just uses the block layer). So
if we fix iommu, then we can remove a workaround to fix sg lists in
llds.


> A key problem I was hoping would be solved with your work here was the 
> elimination of that post dma_map_sg() split.

Yeah, that's my goal too.


> If I understood James and Ben correctly, one of the key problems was 
> always in communicating libata's segment boundary needs to the IOMMU layers?
> 
> 	Jeff
>