SATA DVD issue...

SATA DVD issue...

[Nils Faerber]

Hello!
I am trying to use a SATA DVD burner on a Marvell Kirkwood based
platform, kernel is currently based on vanilla 2.6.34 with only board
specific patches.

SATA in general works just fine with harddisks.

But when I attach my DVD drive any data read or write access triggers a
BUG() in libata-sff.c:

ata_bmdma_qc_issue():
...
        /* see ata_dma_blacklisted() */
        BUG_ON((ap->flags & ATA_FLAG_PIO_POLLING) &&
               qc->tf.protocol == ATAPI_PROT_DMA);
...

Command access (e.g. to eject the media or to erase a R/W disc) do work.

My knowledge about ATA and SATA is quite limited so I cannot really
interpret this issue.

After some looking around and with the hint in the comment I tried
blacklisting my drive, so I added an entry to libata-core.c:

        { "HL-DT-ST DVDRAM GH22LS50", "TL01",           ATA_HORKAGE_NODMA },

Now the drive works but it is awefully slow - reading just a little over
1MB/s - well, without DMA mode this is quite expectable.

I suspect that the Marvell SATA host driver should be OK and is not in
fault - it is widely used in PCI setups and the SOC variant does almost
not differ. And I also suspect that the above "fix" is not the best way
to do it.
I also tried the same driver with a USB-SATA connector (I do not have a
SATA PC at hand right now) and there it behaves pretty normal with 5 to
10 times higher read rates.


I would be more than happy if someone could help me diagnosing and
especially fixing this problem. If I can give more information or try
different things on the board just let know!

Many thanks in advance!

Cheers
  nils

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