linux-kernel - Re: [PATCH] dma-debug: disable DMA_API

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Date:	Fri, 5 Jun 2009 15:57:56 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	joerg.roedel@....com, torvalds@...ux-foundation.org, mingo@...e.hu,
	lethal@...ux-sh.org, just.for.lkml@...glemail.com,
	hancockrwd@...il.com, jens.axboe@...cle.com, bharrosh@...asas.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH] dma-debug: disable DMA_API_DEBUG for now

On Friday 05 June 2009, FUJITA Tomonori wrote:
> I think that the better fix can handle both cases per device:
> 
> - multiple identical dma addresses should not happen (with devices
>   behind hardware IOMMU)
> - multiple identical dma addresses could happen

I guess you could also have the case where for a given range
of addresses, you use a linear mapping and the dma addresses
can be identical, while for other physical addresses you would
rely on address translation.

For example on PowerPC/Cell with infiniband adapters, you can get
linear mapping behavior for DMA_ATTR_WEAK_ORDERING but IOMMU
translation without that flag, for the same device and same
physical address.

	Arnd <><
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