linux-kernel - RE: [PATCH]iwlan dma mapping read and write changes

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Date:	Wed, 11 Feb 2009 23:41:38 +0200
From:	"Winkler, Tomas" <tomas.winkler@...el.com>
To:	Johannes Berg <johannes@...solutions.net>
CC:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.sc.intel.com>,
	"Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>,
	"Zhu, Yi" <yi.zhu@...el.com>, Chris Wright <chrisw@...s-sol.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: RE: [PATCH]iwlan dma mapping read and write changes



>-----Original Message-----
>From: Johannes Berg [mailto:johannes@...solutions.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@...ts.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@...el.com>
>> Acked-by: Tomas Winkler <tomas.winkler@...el.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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