linux-kernel - Re: [PATCH 5/6] firewire: SBP-2 highlevel driver

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Date:	Thu, 03 May 2007 00:10:07 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Christoph Hellwig <hch@...radead.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux-kernel@...r.kernel.org, Kristian H??gsberg <krh@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux1394-devel <linux1394-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 5/6] firewire: SBP-2 highlevel driver

I wrote:
> Christoph Hellwig wrote:
>>> +	/* Convert the scatterlist to an sbp2 page table.  If any
>>> +	 * scatterlist entries are too big for sbp2 we split the as we go. */
>> Please set the max_sectors value in your host template so that the
>> block layer doesn't build sg entries too big for you.
> 
> Hmm, what about this:
> 
> James Bottomley wrote on 2007-01-15:
> | Actually, there's one unfortunate case where Linux won't respect this:
> | an IOMMU that can do virtual merging.  This parameter is a block queue
> | parameter, so block will happily make sure the request segments obey it.
> | However, when you get to dma_map_rq() it doesn't see the segment limits,
> | so, if the iommu merges, you can end up with SG elements the other side
> | that violate this.  I've been meaning to do something about this for
> | ages (IDE is the other subsystem that has an absolute requirement for a
> | fixed maximum segment size) but never found an excuse to fix it.
> 
> http://marc.info/?l=linux-scsi&m=116889641203397

PS:
Nonetheless, yes, fw-sbp2.c is curiously missing to set the template's
max_sectors.
-- 
Stefan Richter
-=====-=-=== -=-= ---==
http://arcgraph.de/sr/
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