netdev - Re: [PATCH v3 2/2][BNX2]: Add iSCSI support to BNX2 devices.

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Message-ID: <46FB6837.7040308@garzik.org>
Date:	Thu, 27 Sep 2007 04:22:15 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	benh@...nel.crashing.org
CC:	FUJITA Tomonori <tomof@....org>, hare@...e.de,
	open-iscsi@...glegroups.com, hch@...radead.org,
	davem@...emloft.net, mchristi@...hat.com, netdev@...r.kernel.org,
	anilgv@...adcom.com, talm@...adcom.com, lusinsky@...adcom.com,
	uri@...adcom.com, fujita.tomonori@....ntt.co.jp
Subject: Re: [PATCH v3 2/2][BNX2]: Add iSCSI support to BNX2 devices.

Benjamin Herrenschmidt wrote:
> On Thu, 2007-09-27 at 03:49 -0400, Jeff Garzik wrote:
>> Benjamin Herrenschmidt wrote:
>>> On Thu, 2007-09-27 at 03:31 -0400, Jeff Garzik wrote:
>>>> A key problem I was hoping would be solved with your work here was
>>>> the 
>>>> elimination of that post dma_map_sg() split.
>>>>
>>>> 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?
>>> Yup. If we can put some constraint in struct device that the dma mapping
>>> code can then look at ... we also need to ensure that what's passed in
>>> for DMA'ing already matches those constraints as well since no-iommu
>>> platforms will basically just keep the dma table as-is.
>> That's a good point...  no-iommu platforms would need to be updated to 
>> do the split for me.  I suppose we can steal that code from swiotlb or 
>> somewhere.
> 
> Doing the split means being able to grow the sglist... which the dma_*
> calls can't do at least not in their current form.

IMO one straightforward approach is for the struct scatterlist owner to 
provide a table large enough to accomodate the possible splits (perhaps 
along with communicate that table's max size to the IOMMU/dma layers).

	Jeff


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