linux-kernel - Re: [RFC 0/5] ARM: dma-mapping: New dma_map

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Message-ID: <505A7DB4.4090902@wwwdotorg.org>
Date:	Wed, 19 Sep 2012 20:21:40 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Krishna Reddy <vdumpa@...dia.com>
CC:	Joerg Roedel <joerg.roedel@....com>, Arnd Bergmann <arnd@...db.de>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"minchan@...nel.org" <minchan@...nel.org>,
	"chunsang.jeong@...aro.org" <chunsang.jeong@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"subashrp@...il.com" <subashrp@...il.com>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"pullip.cho@...sung.com" <pullip.cho@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 0/5] ARM: dma-mapping: New dma_map_ops to control IOVA more
 precisely

On 09/19/2012 07:44 PM, Krishna Reddy wrote:
>> When a device driver would only use the IOMMU-API and needs small DMA-
>> able areas it has to re-implement something like the DMA-API (basically an
>> address allocator) for that. So I don't see a reason why both can't be used in a
>> device driver.
> 
> On Tegra, the following use cases need specific IOVA mapping.
> 1. Few MMIO blocks need IOVA=PA mapping setup.

In that case, why would we enable the IOMMU for that one device; IOMMU
disabled means VA==PA, right? Perhaps isolation of the device so it can
only access certain PA ranges for security?
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