linux-kernel - Re: PowerPC PCI DMA issues (prefetch/coherency?)

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Message-Id: <200906161943.38764.arnd@arndb.de>
Date:	Tue, 16 Jun 2009 19:43:38 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linuxppc-dev@...ts.ozlabs.org
Cc:	Scott Wood <scottwood@...escale.com>,
	Chris Pringle <chris.pringle@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: PowerPC PCI DMA issues (prefetch/coherency?)

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

	Arnd <><
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