Re: [Alsa-devel] Re: [OT] ALSA userspace API complexity

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Llu, 2006-01-09 at 16:29 -0800, David Lang wrote:
> I was under the (apparently mistaken) impression that you couldn't DMA 
> from userspace (something to do with the possibility that the userspace 
> memory pages could be swapped out in the middle of the DMA)

Drivers can choose to support this two different ways. One is to have a
buffer of kernel memory mapped into user space and shared with the
hardware (this is how OSS did it), the other is to use the 2.6
get_user_pages API to get the physical address of a set of pages and
lock them down so they don't wander off during DMA.

Both have advantages for different uses.

Alan

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