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From: Arnd Bergmann <arnd@arndb.de>
To: linuxppc-dev@ozlabs.org
Subject: Re: powerpc: DMA coherent allocations broken for
	CONFIG_NOT_COHERENT_CACHE
Date: Mon, 25 May 2009 02:43:14 +0100
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On Monday 25 May 2009, Benjamin Herrenschmidt wrote:
> Note that I still think the right approach in the long run is to ban the
> consistent allocs from atomic contexts generically in linux, though that
> will be a hard nut to crack.

I might be missing too much context here, but can't we make drivers that
need this allocate an uncached memory range at setup time and call
dma_declare_coherent_memory() on that to make a later dma_alloc_coherent()
succeed without GFP_KERNEL?

If that is not enough, dma_alloc_coherent could be changed to
try dma_alloc_from_coherent() on the bridge device (PCI HB,
PLB4, ...), if we reserve a reasonably sized amount of uncached
memory for each bridge that has noncoherent devices.

	Arnd <><