On Tue, Oct 22, 2002 at 03:13:09PM -0500, Frank C. Earl wrote: > On Tuesday 22 October 2002 03:00 pm, you wrote: > > > But wouldnt it be nice to allow the graphics card to directly access > > the data from user space ? > > It seems to defeat the whole point of DMA, if you have to do multiple > > copies of the data. > > DMA allows you to do other things while the display chip's busy. DMA with > the RagePRO isn't safe (as in, can be reliably secured against malicious > clients using it to do exploits, etc...) so you have to audit the stream and > unmap the buffer (which will cause all kinds of cache miss pains per > Linus...) or copy the data across and DMA it from there. The copy method is > probably going to be faster than an audit and unmap because everything is in > cache with the copy operation.
I would recommend an audit then a copy, with the DMA buffer being setup as non-cached, write combining memory (like AGP mapped memory). The reason being that you don't want to pollute the cache with blocks that are essentially write-once. -- Smile! http://antwrp.gsfc.nasa.gov/apod/ap990315.html ------------------------------------------------------- This sf.net emial is sponsored by: Influence the future of Java(TM) technology. Join the Java Community Process(SM) (JCP(SM)) program now. http://ad.doubleclick.net/clk;4699841;7576301;v?http://www.sun.com/javavote _______________________________________________ Dri-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/dri-devel
