Subject: Re: [patch 1/1] powerpc: enable ARCH_DMA_ADDR_T_64BIT with ARCH_PHYS_ADDR_T_64BIT

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sat, 02 Oct 2010 13:20:54 +1000

On Fri, 2010-10-01 at 21:31 -0400, Josh Boyer wrote:
> > +config ARCH_DMA_ADDR_T_64BIT
> > +       def_bool ARCH_PHYS_ADDR_T_64BIT
> > +
> 
> I seemed to have missed what this is about entirely.  Is there some
> place I can look that describes what that is supposed to do?  The PPC
> 4xx boards set PHYS_ADDR_T_64BIT because the MMU uses 36 bit
> addressing, but the CPU is only 32 bits.  I want to make sure this DMA
> thing isn't going to cause problems. 

Yes, we need to test a bit. Our dma_addr_t has remained 32-bit so far
because despite the fact that we've had routinely to deal with >32-bit
physical addresses for MMIO, physical memory support has been
constrained afaik to 32-bit.

We might be better off keeping this as something individual platforms
can select...

Cheers,
Ben.