On Thu, Mar 16, 2000 at 11:48:17AM -0500, John Wilson wrote:
> On Thu, Mar 16, 2000 at 08:22:38AM -0500, Richard B. Johnson wrote:
> > No. Not a "user-buffer". It may be possible to memory-map something that's
> > DMA..able to user space, but even that's not guaranteed. To have something
> > DMA..able in the ix86 machines, it needs to be:
> >
> > (1) Physical, below 16 Megabytes
> > (2) DATA alignment must be such that a 64k block is not crossed
> > during a DMA transfer. The ix86 machines use a page register
> > to access 64k pages.
> > (3) You need access to the DMA controller which the kernel isn't
> > going to give you, without a fight iopl(3), etc., from user-
> > space.
>
> No no, these requirements are for ISA DMA, not DMA in general. I'm using
> a PCI device, so there are no address restrictions (on x86 anyway, I dunno
> how PCI works on CPUs with >32 addr bits), and it has its own DMA paging
> registers so it doesn't require a contiguous buffer either. The buffer
> just has to be locked in place, which sounds like mlock() would be my friend.
>
> Also, my driver is a real driver, it doesn't run in user space. I just want
> it to be able to set the device up so that the DMA buffer (*only*) is in
> user space, and let 'er rip.
You're looking for kiobufs. They're in 2.3, not in 2.2 but available
as a patch for 2.2.
--
Andreas E. Bombe <andreas.bombe@munich.netsurf.de>
http://home.pages.de/~andreas.bombe/ DSA key 0x04880A44
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