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

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Date:	Fri, 16 Jul 2010 17:01:08 -0700
From:	Larry Bassel <lbassel@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Tim HRM <zt.tmzt@...il.com>,
	Zach Pfeffer <zpfeffer@...eaurora.org>,
	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 16 Jul 10 08:58, Russell King - ARM Linux wrote:
> On Thu, Jul 15, 2010 at 08:48:36PM -0400, Tim HRM wrote:
> > Interesting, since I seem to remember the MSM devices mostly conduct
> > IO through regions of normal RAM, largely accomplished through
> > ioremap() calls.
> > 
> > Without more public domain documentation of the MSM chips and AMSS
> > interfaces I wouldn't know how to avoid this, but I can imagine it
> > creates a bit of urgency for Qualcomm developers as they attempt to
> > upstream support for this most interesting SoC.
> 
> As the patch has been out for RFC since early April on the linux-arm-kernel
> mailing list (Subject: [RFC] Prohibit ioremap() on kernel managed RAM),
> and no comments have come back from Qualcomm folk.

We are investigating the impact of this change on us, and I
will send out more detailed comments next week.

> 
> The restriction on creation of multiple V:P mappings with differing
> attributes is also fairly hard to miss in the ARM architecture
> specification when reading the sections about caches.
> 

Larry Bassel

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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