Message-ID: <4A37DB0F.7060801@freescale.com>
Date: Tue, 16 Jun 2009 12:49:03 -0500
From: Scott Wood <scottwood@freescale.com>
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To: Arnd Bergmann <arnd@arndb.de>
CC: linuxppc-dev@lists.ozlabs.org, Chris Pringle <chris.pringle@oxtel.com>,
       linux-kernel@vger.kernel.org
Subject: Re: PowerPC PCI DMA issues (prefetch/coherency?)
References: <4A37A503.3030209@oxtel.com> <4A37CF02.5080906@oxtel.com> <4A37D073.6020802@freescale.com> <200906161943.38764.arnd@arndb.de>
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Arnd Bergmann wrote:
> On Tuesday 16 June 2009, Scott Wood wrote:
>> Chris Pringle wrote:
>>> Ah right - that would explain what we're seeing then... Doh. Thought I 
>>> might have been onto something then. Is there any way to force a cache 
>>> flush? That'd at least prove it was a caching issue if it resolved the 
>>> problem.
>> You could enable CONFIG_NOT_COHERENT_CACHE.
> 
> If the whole system is noncoherent, that is the right solution.

I meant it more as a test than a permanent solution...

> If the
> device is the only one, you can also use dma_alloc_noncoherent() and
> flush explicitly with dma_cache_sync().

I don't see how that would help -- aren't those also controlled by 
CONFIG_NOT_COHERENT_CACHE?

-Scott
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