netdev - Re: [PATCH 3/20][BNX2]: Add 40-bit DMA workaround for 5708.

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Message-Id: <20070502.144538.68132264.davem@davemloft.net>
Date:	Wed, 02 May 2007 14:45:38 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mchan@...adcom.com
Cc:	jeff@...zik.org, netdev@...r.kernel.org
Subject: Re: [PATCH 3/20][BNX2]: Add 40-bit DMA workaround for 5708.

From: "Michael Chan" <mchan@...adcom.com>
Date: Wed, 02 May 2007 14:27:49 -0700

> I see.  So IA64 always uses the SWIOTLB when it doesn't have IOMMU then?
> 
> I'm a bit confused.  Is it enough to just set the DMA mask to 40-bit and
> forget about all this checking?  I thought that wasn't enough.  A tx
> packet can be anywhere in 64-bit memory.  When it gets to the driver,
> pci_map will not do any translation even if DMA mask is set to 40-bit if
> it doesn't have IOMMU.  Is that right?

If the buffer doesn't meet the DMA mask specification, it should do
bounce buffering.

Have a look at lib/swiotlb.c, that is exactly what it appears to
be doing.
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