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From: Kumar Gala <galak@kernel.crashing.org>
To: Trent Piepho <tpiepho@freescale.com>
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Subject: Re: How to support 3GB pci address?
Date: Thu, 11 Dec 2008 23:08:50 -0600
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On Dec 11, 2008, at 10:07 PM, Trent Piepho wrote:

> On Thu, 11 Dec 2008, Kumar Gala wrote:
>> On Dec 11, 2008, at 6:04 AM, maillist.kernel wrote:
>>> In the system, the total PCI address needed is about 3GB, so I  
>>> want to know
>>> how to support it in linux. mpc8548 has 36-bit real address, and can
>>> support 32GB PCIE address space, but in linux, there is only 1GB  
>>> kernel
>>> space, how to map the 3GB pci address to kernel? Is the  36-bit real
>>> address only used to support large memory(>4GB) for muti-threads?
>>
>> The 36-bit support is current (in tree) in complete.  Work is in  
>> progress to
>> add swiotlb support to PPC which will generically enable what you  
>> want to
>> accomplish.
>
> Don't the ATMU windows in the pcie controller serve as a IOMMU,  
> making swiotlb
> unnecessary and wasteful?

Nope.  You have no way to tell when to switch a window as you have no  
idea when a device might DMA data.

- k