Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit

[Becky Bruce]

On May 26, 2009, at 7:51 AM, Ian Campbell wrote:

> On Fri, 2009-05-22 at 19:55 -0400, Jeremy Fitzhardinge wrote:
> > Ian Campbell wrote:
> > > On Thu, 2009-05-21 at 14:27 -0400, Becky Bruce wrote:
> > >
> > > > I can work with that, but it's going to be a bit inefficient, as I
> > > > actually need the dma_addr_t, not the phys_addr_t, so I'll have to
> > > > convert.  In every case, this is a conversion I've already done and
> > > > that I need in the calling code as well.
> > >
> > > Does
> > >
> > >    dma_addr_t dma_map_range(struct device *hwdev, phys_addr_t addr,
> > >    size_t size);
> > >
> > > work for you?
> > >
> > > If the range does not need mapping then it returns the dma  
> > > address, if
> > > you needed to calculate the dma address anyway to figure out if  
> > > mapping
> > > is required then this is fine. If the range does need mapping then  
> > > it
> > > returns NULL.
> >
> > My only concern is whether dma_addr_t == 0 is actually equivalent to
> > NULL.  That is, can we be sure that address 0 will never be used?
>
> It seems not, ~0UL might have been an option, but...
>
> > Taking dma_alloc_coherent as a model, we could have something like:
> >
> >    int dma_map_range(struct device *hwdev, phys_addr_t addr, size_t  
> > size, dma_addr_t *dma_addrp);
> >
> >
> > where *dma_addrp is set if the function returns success (bool return
> > type might be clearer).
>
> ... this sounds like a good idea to me.

I agree.  This will work for me as well.

-becky

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