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Subject: Re: [PATCH] powerpc: Change archdata dma_data type to dma_addr_t
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Christoph Hellwig <hch@lst.de>
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Date: Wed, 26 Aug 2009 22:29:50 +1000
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On Mon, 2009-08-24 at 21:48 +0200, Christoph Hellwig wrote:
> On Mon, Aug 24, 2009 at 11:17:14AM -0500, Becky Bruce wrote:
> > Previously, this was specified as a void *, but that's not
> > large enough on 32-bit systems with 36-bit physical
> > addressing support.  Change the type to dma_addr_t so it
> > will scale based on the size of a dma address.
> 
> This looks extreml ugly to me.  It seems like the typical use is to
> store a pointer to a structure.  So what about making the direct
> dma case follow that general scheme instead?
> 
> E.g. declare a
> 
> struct direct_dma_data {
> 	dma_addr_t	direct_dma_offset;
> };
> 
> and have one normal instace of it, and one per weird cell device.

Right, but we want to avoid a structure for the classic case of 32-bit
systems with no iommu... 

I wouldn't mind doing a union here. 

The other option is to have a global somewhere that we make that point
to or something like that but it's probably even more ugly.

Cheers,
Ben.