linux-kernel - Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management

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Message-ID: <20100714220536.GE18138@n2100.arm.linux.org.uk>
Date:	Wed, 14 Jul 2010 23:05:36 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Zach Pfeffer <zpfeffer@...eaurora.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	ebiederm@...ssion.com, linux-arch@...r.kernel.org,
	dwalker@...eaurora.org, mel@....ul.ie,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, andi@...stfloor.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device
	memory management

On Wed, Jul 14, 2010 at 01:11:49PM -0700, Zach Pfeffer wrote:
> If the DMA-API contained functions to allocate virtual space separate
> from physical space and reworked how chained buffers functioned it
> would probably work - but then things start to look like the VCM API
> which does graph based map management.

Every additional virtual mapping of a physical buffer results in
additional cache aliases on aliasing caches, and more workload for
developers to sort out the cache aliasing issues.

What does VCM to do mitigate that?
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