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

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Message-ID: <4A38A21B.5060306@oxtel.com>
Date:	Wed, 17 Jun 2009 08:58:19 +0100
From:	Chris Pringle <chris.pringle@...el.com>
To:	Scott Wood <scottwood@...escale.com>
CC:	linux-kernel@...r.kernel.org,
	"linuxppc-dev@...abs.org list" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: PowerPC PCI DMA issues (prefetch/coherency?)


> You could enable CONFIG_NOT_COHERENT_CACHE.
>
I've just tried this (I had to edit Kconfig in power/platforms to make 
the build system accept it), and interestingly it's making no 
difference. I'm using streaming mappings, and are using the pci_map_sg 
functions to ensure the memory is mapped/flushed correctly. I've also 
explicitly put in a pci_dma_sync_sg_for_device, however that's also not 
made any difference. Turning the cpu cache snoop off has the same affect 
as it did without CONFIG_NOT_COHERENT_CACHE; it gets much worse. Any 
other ideas?

Will back off the low latency patches next, and give 2.6.30 a try - see 
if that makes any difference.

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