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

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Message-ID: <1178141269.4820.109.camel@dell>
Date:	Wed, 02 May 2007 14:27:49 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"David Miller" <davem@...emloft.net>
cc:	jeff@...zik.org, "netdev" <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/20][BNX2]: Add 40-bit DMA workaround for 5708.

On Wed, 2007-05-02 at 12:40 -0700, David Miller wrote:
> From: "Michael Chan" <mchan@...adcom.com>
> Date: Wed, 2 May 2007 08:23:40 -0700
> 
> > A non-IOMMU system using 64-bit dma_addr_t will always set
> > CONFIG_HIGHMEM, right?
> 
> Nope, IA-64 is at least one example.
> 
> IA-64 has both IOMMU and non-IOMMU configurations, and
> never sets HIGHMEM.
> 

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?

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