Re: [RFT][PATCH] generic device DMA implementation

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

>>- There's no analogue to pci_pool, and there's nothing like
>>   "kmalloc" (likely built from N dma-coherent pools). 
> 
> 
> I didn't want to build another memory pool re-implementation.  The mempool API 
> seems to me to be flexible enough for this, is there some reason it won't work?

I didn't notice any way it would track, and return, DMA addresses.
It's much like a kmem_cache in that way.


> I did consider wrappering mempool to make it easier, but I couldn't really 
> find a simplifying wrapper that wouldn't lose flexibility.

In My Ideal World (tm) Linux would have some kind of memory allocator
that'd be configured to use __get_free_pages() or dma_alloc_coherent()
as appropriate.  Fast, efficient; caching pre-initted objects; etc.

I'm not sure how realistic that is.  So long as APIs keep getting written
so that drivers _must_ re-invent the "memory allocator" wheel, it's not.

But ... if the generic DMA API includes such stuff, it'd be easy to replace
a dumb implementation (have you seen pci_pool, or how usb_buffer_alloc
works? :) with something more intelligent than any driver could justify
writing for its own use.

- Dave