Message-ID: <4C2D965F.5000206@codeaurora.org>
Date: Fri, 02 Jul 2010 00:33:51 -0700
From: Zach Pfeffer <zpfeffer@codeaurora.org>
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To: Daniel Walker <dwalker@codeaurora.org>
CC: Andi Kleen <andi@firstfloor.org>, Randy Dunlap <randy.dunlap@oracle.com>,
       mel@csn.ul.ie, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       linux-arm-msm@vger.kernel.org, linux-omap@vger.kernel.org,
       linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager
References: <1277877350-2147-1-git-send-email-zpfeffer@codeaurora.org>  <1277877350-2147-3-git-send-email-zpfeffer@codeaurora.org>  <20100701101746.3810cc3b.randy.dunlap@oracle.com>  <20100701180241.GA3594@basil.fritz.box>  <1278012503.7738.17.camel@c-dwalke-linux.q <1278021944.7738.43.camel@c-dwalke-linux.qualcomm.com>
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Daniel Walker wrote:
> On Thu, 2010-07-01 at 15:00 -0700, Zach Pfeffer wrote:
> 
> 
>> Additionally, the current IOMMU interface does not allow users to
>> associate one page table with multiple IOMMUs unless the user explicitly
>> wrote a muxed device underneith the IOMMU interface. This also could be
>> done, but would have to be done for every such use case. Since the
>> particular topology is run-time configurable all of these use-cases and
>> more can be expressed without pushing the topology into the low-level
>> IOMMU driver.
>>
>> The VCMM takes the long view. Its designed for a future in which the
>> number of IOMMUs will go up and the ways in which these IOMMUs are
>> composed will vary from system to system, and may vary at
>> runtime. Already, there are ~20 different IOMMU map implementations in
>> the kernel. Had the Linux kernel had the VCMM, many of those
>> implementations could have leveraged the mapping and topology management
>> of a VCMM, while focusing on a few key hardware specific functions (map
>> this physical address, program the page table base register).
> 
> So if we include this code which "map implementations" could you
> collapse into this implementations ? Generally , what currently existing
> code can VCMM help to eliminate?

In theory, it can eliminate all code the interoperates between IOMMU,
CPU and non-IOMMU based devices and all the mapping code, alignment,
mapping attribute and special block size support that's been
implemented.


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