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Re: Linear address mapping
- To: Mailing List Recipients <pci-sig-request@znyx.com>
- Subject: Re: Linear address mapping
- From: "John R Pierce" <pierce@scruznet.com>
- Date: Fri, 27 Sep 1996 11:43:05 -0700
- Cc: <pci-sig@znyx.com>
- Resent-Date: Fri, 27 Sep 1996 11:43:05 -0700
- Resent-From: pci-sig-request@znyx.com
- Resent-Message-Id: <"Fn1ad3.0.oH7.OE2Jo"@dart>
- Resent-Sender: pci-sig-request@znyx.com
Stephen Williams <steve@icarus.com> wrote...
>
> pierce@scruznet.com said:
> > if your device is intended to operate in a virtual memory environment
> > (windows, NT, *nix, OS/2), then it will either have to use small
> > static DMA buffers or it will have to support "scatter/gather".
>
> In Linux, you do not need to go through all of this. Memory allocated
> in kernel mode maps 1-to-1 to physical, so there is no problem. I've
> written Linux drivers for devices with pretty large DMA transfers.
Ah. So Linux generally doesn't support DMA straight into or out of user space?
That was what I was really referring to. The original poster was talking about
1/2Meg DMA xfers, I can't quite see tieing up 1/2MEG in kernel mode on a
typical linux system for a DMA buffer!
-jrp
C