RE: Question regarding DMA xfer to user space directly

From: Alan Shih (
Date: Wed Jul 09 2003 - 12:35:15 EST

Next question would be what are the steps that the driver need to ping user
pages before setting up the xfer?


-----Original Message-----
From: Alan Cox []
Sent: Tuesday, July 08, 2003 8:22 AM
To: Alan Shih
Cc: Linux Kernel Mailing List
Subject: Re: Question regarding DMA xfer to user space directly

On Maw, 2003-07-08 at 15:50, Alan Shih wrote:
> Is there a provision in MM for DMA transfer to user space directly without
> allocating a kernel buffer?

Yes. Its used both for O_DIRECT I/O (direct to disk I/O from userspace)
and for things like tv capture cards. The kernel allows a driver to pin
user pages and obtain mappings for them. Note that for large systems
user pages may be above the 32bit boundary so you need DAC capable
hardware to get the best results

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