linux-kernel - Re: [PATCH] drivers/ata: Add the SW NCQ support to sata

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Date:	Fri, 18 May 2007 10:34:35 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Robert Hancock <hancockr@...w.ca>,
	Zoltan Boszormenyi <zboszor@...aweb.hu>,
	Peer Chen <pchen@...dia.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/ata: Add the SW NCQ support to sata_nv for MCP51/MCP55/MCP61

Alan Cox wrote:
>> That shouldn't be a problem, libata default DMA mask is 32 bits (which 
>> isn't overridden with this controller) and so the block layer will 
>> bounce any data being read/written above that point with IOMMU or 
>> swiotlb. The comment is a bit unnecessarily scary.
> 
> Adding a BUG_ON for this would be wise. Its trivial to check and a BUG
> rather than corruption if this assumption ever changes would be far
> preferable

The default DMA mask -everywhere- is 32 bits.

A lot of code will break if this assumption ever changes, not just libata.

	Jeff



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