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Date: Fri, 7 Aug 2009 08:15:01 -0500
From: Robin Holt <holt@sgi.com>
To: Laurent Desnogues <laurent.desnogues@gmail.com>
Cc: Jamie Lokier <jamie@shareable.org>,
       Russell King - ARM Linux <linux@arm.linux.org.uk>,
       Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
       David Xiao <dxiao@broadcom.com>, Ben Dooks <ben-linux@fluff.org>,
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	<linux-arm-kernel@lists.arm.linux.org.uk>
Subject: Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is
	get_user_pages() enough to prevent pages from being swapped out ?")
Message-ID: <20090807131501.GD2763@sgi.com>
References: <200908061208.22131.laurent.pinchart@ideasonboard.com> <20090806222543.GG31579@n2100.arm.linux.org.uk> <1249624766.32621.61.camel@david-laptop> <200908070958.31322.laurent.pinchart@ideasonboard.com> <20090807081041.GB18343@n2100.arm.linux.org.uk> <20090807095426.GI8725@shareable.org> <761ea48b0908070507n5c580455pb86e5240a7cf6c0c@mail.gmail.com>
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On Fri, Aug 07, 2009 at 02:07:43PM +0200, Laurent Desnogues wrote:
> On Fri, Aug 7, 2009 at 11:54 AM, Jamie Lokier<jamie@shareable.org> wrote:
> >
> > 1. Does the architecture not prevent speculative instruction
> > prefetches from crossing a page boundary?  It would be handy under the
> > circumstances.
> 
> There's no such restriction in ARMv7 architecture.

Doesn't it prevent them for uncached areas?  I _THOUGHT_ there was an
alloc_consistent (or something like that) call on ARM which gave you
an uncached mapping where you could do DMA.  I also thought there was
a dma_* set of functions which remapped as uncached before DMA begins
and remapped as normal after DMA has been completed.

Sorry for the fuzzy recollection.  I am dredging from 2.6.21 timeframe.

Robin