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Date:	Wed, 27 Jun 2007 08:48:48 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jeff Garzik <jeff@...zik.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [git patches] libata fixes



On Wed, 27 Jun 2007, Jeff Garzik wrote:
> 
> Such would be a diagnostic that would trigger on valid SCSI commands, when the
> user is doing nothing wrong and the system can indeed complete the command
> just fine.  Additionally, this is moving us in the direction of what the IDE
> driver has apparently been doing.

Indeed. At least the IDE CD-ROM driver does

	if ((rq->data_len & 15) || (addr & mask))
		info->dma = 0;

where the "mask" is the dma_alignment mask. So it requires the length to 
be a multiple of 16, and also requires a certain alignment of the data 
(which defaults to 32 bytes for some reason I cannot for the life of me 
remember).

The generic BIO layer does that DMA alignment check too when mapping user 
pages.

		Linus
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