Understanding DMA/NoDMA options and fixes

Rick Stevens rstevens at vitalstream.com
Thu Jul 21 20:57:47 UTC 2005

Alan Cox wrote:
> On Llu, 2005-07-18 at 21:02 -0500, John Best wrote:
>>Are there jumpers on the IDE devices that should be looked
>>at/investigated?   If I hooked up devices using Cable Select vs
>>physically jumpering devices to primary/secondary will it make any

Sorry to break in, Alan.  Cable select is bloody evil.  Do not use it
if you value your sanity.  IMHO after dealing with over 3,000 Linux-
based servers, "Cable select:  Just say 'No'."

>>             Can I tell which device or devices are responsible for the
>>DMA issues?  Can I tell when buying or looking at a device whether it
>>supports the proper dma standards?  Can I go to a web site or other
>>location to check for compatible dma devices?
> Its almost certainly a Linux problem, especially if it worked before
> FC3. There are afaik no devices sold today (or in recent history) with
> broken DMA. There are however limitations on some older controllers.
> Those limitations haven't mysteriously changed in FC3/4 however.
> Please file a bug and assign it to my work incarnation <alan at redhat...>.
> Include the controller in question, lspci -v output, the devices
> attached and dmesg output.
> Alan

- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
- Millihelen, adj: The amount of beauty required to launch one ship. -

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