DMA bug with ata_piix on ICH7-M

[Ben Whitten <benwhitten@gmail.com>]

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Hi,
I seem to have found a problem with DMA on a motherboard using an ICH7-M
chipset, this bug prevents me from installing to the harddrive and I
have been unable to find a workaround.
The motherboard is a Unicorn computers ENDAT-2794A motherboard[1]
When I try to run the Ubuntu 11.10 USB install image which is using
kernel 3.0 the system jams for a good few minutes at a stage in boot
then eventually comes up. In the dmesg I see the following;

[  332.656551] ata1.01: configured for UDMA/33
[  332.656590] ata1: EH complete
[  332.716560] ata1.01: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6
frozen
[  332.716776] ata1.01: BMDMA stat 0x44
[  332.716887] ata1.01: failed command: READ DMA
[  332.717029] ata1.01: cmd c8/00:08:78:03:00/00:00:00:00:00/f0 tag 0
dma 4096 in
[  332.717034]          res 50/00:00:7f:03:00/00:00:12:00:00/f0 Emask
0x2 (HSM violation)
[  332.717435] ata1.01: status: { DRDY }
[  332.717564] ata1: soft resetting link
[  332.900593] ata1.01: configured for UDMA/33
[  332.900631] ata1: EH complete
[  332.949133] ata1.01: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6
frozen
[  332.949344] ata1.01: BMDMA stat 0x44
[  332.949454] ata1.01: failed command: READ DMA
[  332.949593] ata1.01: cmd c8/00:08:90:03:00/00:00:00:00:00/f0 tag 0
dma 4096 in
[  332.949598]          res 50/00:00:97:03:00/00:00:12:00:00/f0 Emask
0x2 (HSM violation)
[  332.950006] ata1.01: status: { DRDY }
[  332.950130] ata1: soft resetting link

Prior to this it gets configured for UDMA/133 which I believe is out of
spec for the ICH7 following information on a previous fixed bug[2]. It
eventually backs it down to 33, which is probably where the system
unlocks and can continue to boot.

I have also tried this with a development snapshot of Ubuntu 12.04 using
kernel 3.2 with the same result.
I have attached a screen shot of the IDE BIOS options in case a default
is wrong or there is a workaround until the bug is fixed. Further system
information and logs can be found on the generated ubuntu launchpad bug
report [3].

Best regards,
Ben Whitten

[1] http://www.unicorn-computer.com.tw/products/itx/2794a.html
[2] http://www.mail-archive.com/linux-ide@vger.kernel.org/msg09509.html
[3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/897777

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