netdev - Re: network devices don't handle pci_dma_mapping

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Date:	Thu, 7 Dec 2006 15:04:16 +0200
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	"Amit S. Kale" <amitkale@...syssoft.com>
Cc:	Stephen Hemminger <shemminger@...l.org>,
	Jeff Garzik <jeff@...zik.org>,
	"Amit S. Kale" <amitkale@...xen.com>, netdev@...r.kernel.org,
	brazilnut@...ibm.com, netxenproj@...syssoft.com, rob@...xen.com,
	romieu@...zoreil.com, sanjeev@...xen.com, wendyx@...ibm.com
Subject: Re: network devices don't handle pci_dma_mapping_error()'s

On Thu, Dec 07, 2006 at 11:48:14AM +0530, Amit S. Kale wrote:

> On the x86_64 boxes that don't feature iommu functionality (because the 
> motherboard disables it or because Linux can't handle it) Linux bounce buffer 
> framework automatically comes into picture. Could we have the same framework 
> take over when IOMMU space is over? I don't think this is possible with 
> present code, though. We probably can have fallback_dma_ops in addition to 
> dma_ops.

In the general case, no - some platforms (including x86-64 on IBM's
high end servers!) have an isolation capable IOMMU, which means all
DMA mappings need to go through it, so a general mechanism to cope
with DMA mappings running out is still needed.

Cheers,
Muli
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