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SubjectRE: [PATCH]iwlan dma mapping read and write changes


>-----Original Message-----
>From: Johannes Berg [mailto:johannes@sipsolutions.net]
>Sent: Wednesday, February 11, 2009 11:34 PM
>To: Winkler, Tomas
>Cc: Yu, Fenghua; David Woodhouse; Ingo Molnar; Stephen Rothwell; Andrew
>Morton; Grumbach, Emmanuel; Zhu, Yi; Chris Wright; LKML; iommu@lists.linux-
>foundation.org
>Subject: RE: [PATCH]iwlan dma mapping read and write changes
>
>On Wed, 2009-02-11 at 23:27 +0200, Winkler, Tomas wrote:
>
>> >mapping with PCI_DMA_TODEVICE which is read only in mapping PTE. But
>iwlan
>> >device
>> >actually writes to the mapped page to update its contents. This issue is
>> >not
>> >exposed in swiotlb. But VT-d hardware can capture this fault and stop
>the
>> >fault
>> >transaction.
>> >
>> >The following patch fixes the issue.
>> >
>> >Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
>> Acked-by: Tomas Winkler <tomas.winkler@intel.com>
>>
>> Indeed the firmware/ucode write back to host memory to update retry
>> counter for APMDU packets. I'm not sure if this is needed for legacy
>> traffic, though.
>
>I don't think they can be seeing AMPDU packets since that is, well,
>broken?

Currently I'm not aware of any other cases where memory is accessed back but I may have not complete info. Will be back with the answer tomorrow.
Tomas

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