Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m achi ne

Jens Axboe
2001-07-02T08:24:25Z

On Thu, Jun 28 2001, Ben LaHaise wrote:
> On Thu, 28 Jun 2001, David S. Miller wrote:
>
> > Please note that this is nonstandard and undocumented behavior.
> >
> > This is not a supported API at all, and the way 64-bit DMA will
> > eventually be done across all platforms is likely to be different.
>
> Well, what is the standard API to use? All these 64 bit cards in my
> machine really make that 95% cpu usage in bounce buffer copying rather
> depressing.

The current sg list and single mapping functions are useless on 64-bit
(and highmem) anyway. I've used struct sg_list as a scatterlist
replacement for some time that holds a page/offset/length thing instead,
and also used pci_map_page for single mappings.

Using a virtual address for this stuff seems a bit short-sighted to
me...

--
Jens Axboe