linux-kernel - IOMMU and DMA mode of pata

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Date:	Wed, 29 Dec 2010 00:43:36 +0100
From:	Steffen Moser <lists@...ffen-moser.de>
To:	linux-kernel@...r.kernel.org
Subject: IOMMU and DMA mode of pata_jmicron

Hi all,

I've encountered a problem with my AMD 890FX based system
and linux-2.6.35.10 (x86_64 platform).

After activating the option "IOMMU" in the mainboard's BIOS
setup, the onboard P-ATA controller "JMicron Technology Corp.
JMB361 AHCI/IDE (rev 02)" puts itself back in the PIO mode.
When loading the module, the kernel reports:

  pata_jmicron 0000:06:00.1: BMDMA: failed to set dma mask, \
                             falling back to PIO

This results, as expected, in a much too low data throughput
between the system and the optical drives connected to the
P-ATA controller.

As soon as I deactivate IOMMU in BIOS setup, the P-ATA channel
runs in the DMA mode again. The S-ATA controllers don't seem
to be affected.

My question is: Is this a known behavior? Are there any
things I have to consider when activating IOMMU (which seems
to be AMD-Vi) on an 890FX based system? Is it a problem of
the chipset and/or the controller or is it related to a
problem in the libata area?

Some information about the affected system:

 - Mainboard:    ASUS M4A89TD Pro/USB3
 - BIOS version: 1101 (most recent version)
 - Chipset:      AMD 890FX
 - Processor:    AMD Phenom 1090T
 - Memory:       4 x 4 GB (Kingston KVR1333D3E9S/4G)
 - Distribution: openSUSE 11.3
 - Kernel:       2.6.35.10 (from "kernel.org"), x86_64

Earlier versions of 2.6.35.x are affected, too. I haven't
tested other kernel versions besides 2.6.35.x, yet.

If you need further information (log files, information from
"/proc", lspci, and so on), please let me know.

Thank you very much in advance for any hint!

Best regards,
Steffen
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