linux-kernel - Re: [PATCH 1/2] arm: msm: Add System MMU support.

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Message-ID: <20100729084018.GM26098@amd.com>
Date:	Thu, 29 Jul 2010 10:40:19 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	"stepanm@...eaurora.org" <stepanm@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"dwalker@...eaurora.org" <dwalker@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] arm: msm: Add System MMU support.

On Thu, Jul 29, 2010 at 04:26:55AM -0400, Arnd Bergmann wrote:
> On Thursday 29 July 2010 05:35:48 FUJITA Tomonori wrote:
> > > 
> > > From what I have been able to tell, the IOMMU interface was written by
> > > AMD/Intel to allow the kvm code to work with a common IOMMU interface. To
> > 
> > Don't confuse the IOMMU interface with the DMA API that Arnd
> > mentioned.
> > 
> > They are not related at all.

Thats not 100% true. They are not strictly related, but they are related
as they may use the same backend kernel drivers to provide their
functionality. Both APIs exist for different purposes, of course.

> Exactly, thanks for the clarification. I also didn't realize that there
> is now an include/linux/iommu.h file that only describes the PCI SR-IOV
> interfaces, unlike the generic IOMMU support that we have in your
> include/linux/dma-mapping.h file.

The IOMMU-API is not about SR-IOV. It is about the capabilities of
modern IOMMU hardware that we can not provide to the kernel with the
DMA-API such as the ability to choose ourself at which io-virtual
address a given cpu physical address should be mapped.
Also I wouldn't call the DMA-API an IOMMU interface. The API does not
depend on an IOMMU which is an important difference to the IOMMU-API.
The IOMMU-API is probably not generic enough to handle all kinds of
IOMMUs but its closer to a generic IOMMU-API than the DMA-API.

		Joerg

-- 
Joerg Roedel - AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

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