Re: DMA API issues

[David Brownell <david-b@pacbell.net>]

James Bottomley wrote:
> On Fri, 2004-06-18 at 16:08, David Brownell wrote:
> 
>>I'm not following you.  This isn't using the PCI DMA calls.
>>These dots don't connect:  different hardware needs different
>>solutions.  How would those calls make dma_alloc_coherent work?
> 
> 
> 
> The statement was "That's dma_alloc_coherent at its core ... it should
> allocate from that 32K region." and what I was pointing out is that not
> all platforms can treat an on-chip memory region as a real memory area. 

But this one can, and it sure seems like the appropriate
solution.  For reasons like the one not quoted above:  it's
a good way to eliminate what would otherwise be a case
where a dmabounce is needed.  And hey wow, it even uses
the API designed to reduce such DMA "mapping" costs, and
there are drivers already using it for such purposes.


> That's why we have the iomem accessor functions.

You mentioned ioremap(), which doesn't help here since
the need is for a block of memory, not just address space,
and also memcpy_toio(), which just another tool to implement
the dma bouncing (which is on the "strongly avoid!" list).

As I said, those still don't make dma_alloc_coherent() work.

- Dave


> James
> 
> 
>