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SubjectPCI DMA question
Date
I've come across something that I would like someone to verify.

It appears that the standard linux kernel lacks a way for a character driver
to DMA data directly to the user buffer.

I was searching for the way to lock pages into memory. This eventually lead
me to the following patch, which doesn't appear to have been added to the
standard kernel at any point:
http://linux-patches.rock-projects.com/v2.2-f/userdma-2.2.5.html

I've also found partial messages where David S. Miller and Linus were
discussing the need for this (Linus mentioned dma_map()), but I couldn't
find enough of the discussion to know if anything was implemented or not.

Since I've got a device that is quite capable of scatter-gather and have no
interest in double copying, it appears that I will need this patch in order
to get reasonable performance.

Is something like this in the 2.3 kernel, or is this yet another patch that
didn't get accepted?

-Bret

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SBS Technologies, Connectivity Products
... solutions for real-time connectivity
Bret Indrelee, Engineer
SBS Technologies, Inc., Connectivity Products
1284 Corporate Center Drive, St. Paul MN 55121
Direct: (651) 905-4731
Main: (651) 905-4700 Fax: (651) 905-4701
E-mail: bindrelee@sbs-cp.com http://www.sbs.com
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