Re: [RFC] generic device DMA implementation

[Jeff Garzik]

David Gibson wrote:
> On Wed, Dec 04, 2002 at 11:47:14AM -0600, James Bottomley wrote:
>>The new DMA API allows a driver to advertise its level of consistent memory 
>>compliance to dma_alloc_consistent.  There are essentially two levels:
>>
>>- I only work with consistent memory, fail if I cannot get it, or
>>- I can work with inconsistent memory, try consistent first but return 
>>inconsistent if it's not available.
> 
> 
> Do you have an example of where the second option is useful?  Off hand
> the only places I can think of where you'd use a consistent_alloc()
> rather than map_single() and friends is in cases where the hardware's
> behaviour means you absolutely positively have to have consistent
> memory.

agreed, good catch.  Returning inconsistent memory when you asked for 
consistent makes not much sense:  the programmer either knows what the 
hardware wants, or the programmer is silly and should not be using 
alloc_consistent anyway.