linux-kernel - Re: Changing IOMMU-API for generic DMA-mapping supported by the hardware

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Date:	Thu, 24 Nov 2011 16:27:47 +0100
From:	'Joerg Roedel' <Joerg.Roedel@....com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	'David Woodhouse' <dwmw2@...radead.org>,
	'Ohad Ben-Cohen' <ohad@...ery.com>,
	'KyongHo Cho' <pullip.cho@...sung.com>,
	'Kai Huang' <mail.kai.huang@...il.com>, <kvm@...r.kernel.org>,
	'Arnd Bergmann' <arnd@...db.de>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
	'Laurent Pinchart' <laurent.pinchart@...asonboard.com>,
	'David Brown' <davidb@...eaurora.org>,
	<linux-omap@...r.kernel.org>,
	'Stepan Moskovchenko' <stepanm@...eaurora.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Changing IOMMU-API for generic DMA-mapping supported by the
 hardware

On Thu, Nov 24, 2011 at 01:52:33PM +0100, Marek Szyprowski wrote:
> In my DMA-mapping IOMMU integration I've used a dma_iommu_mapping structure,
> which contains a pointer to iommu domain, a bitmap and a lock. Maybe we 
> should consider extending iommu domain with allocation bitmap (or other 
> structure that hold information about used/unused iova ranges)? From the
> DMA-mapping (as a IOMMU client) perspective we only need 2 more callbacks
> in IOMMU API: alloc_iova_range() and free_iova_range(). 
> 
> Each IOMMU implementation can provide these calls based on internal bitmap
> allocator which will also cover the issue with reserved ranges. What do you
> think about such solution?

Hmm, the main point of a generic DMA-mapping implementation is that a
common address-allocator will be used. Today every IOMMU driver that
implements the DMA-API has its own allocator, this is something to unify
between for all drivers.

The allocator information can be stored in the default iommu_domain. We
need a user-private pointer there, but that is easy to add.


	Joerg

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