I'm having trouble enabling Intel DCA (Direct Cache Access) feature under 2.6.30.4 kernel.
I compiled the latest version of ixgbe and ioatdma drivers available at intel.com with DCA enabled (CONFIG_DCA). Trying to modprobe under 2.6.30.4 kernel gives me next error from ixgbe driver:
DCA registration failed: -19

Based on the source code, it looks like it thinks no DCA engine is currently available, though ioatdma and dca are loaded. The DCA feature is enabled in the BIOS, and dca_force utility mentioned on some forums did not help.

Has anybody else experienced similar issue? If you're able to get DCA working, what kernel and driver versions are you using?

Turns out not all systems enable I/OAT features in the BIOS, and even though it looks like certain features are enabled, that may not be enough. This is very vendor-specific.