On Wed, Dec 19, 2007 at 08:55:53PM +0100, Manuel Bouyer wrote:
> > It's when the disk is configured that the mode is downgraded:
> > 
> > wd2 at atabus2 drive 0: <WDC WD5000AAKS-00YGA0>
> > wd2: drive supports 16-sector PIO transfers, LBA48 addressing
> > wd2: 465 GB, 969021 cyl, 16 head, 63 sec, 512 bytes/sect x 976773168 sectors
> > wd2(viaide1:0:0): using PIO mode 0
> > 
> >   Does it actually use DMA for the disk(s)?
> 
> No.
> It's strange that the drive doesn't report any supported PIO or DMA mode.

  Thanks for taking a look at this.  If you look at my original posting
in this thread, you'll get a much better idea of what is happening, since
it includes lots of debugging output.  Basically, when the driver is
testing the supported PIO modes, it waits for WDCS_DRQ to be deasserted,
and that never happens.  It times out testing each of the first two PIO modes:

ata_set_mode=0xc
...
__wdcwait: viaide1:0: timeout (time=11), status 58 error 0 (mask 0x8 bits 0x0)
...
ata_set_mode=0xb
...
__wdcwait: viaide1:0: timeout (time=11), status 58 error 0 (mask 0x8 bits 0x0)
...
__wdccommand_done viaide1:0:0 flags 0x108
wd2(viaide1:0:0): using PIO mode 0
  
and then gives up without testing for DMA support.  That's in ata_probe_caps
in ata.c, where a comment says "We didn't find a valid PIO mode.  Assume the
values returned for DMA are buggy too."  BTW: increasing the timeout by a
factor of 100 didn't help, so I don't think it's a timing issue.

  Now status 58 is (from atareg.h):
WDCS_DRDY (drive ready) | WDCS_DSC (drive seek complete) | WDCS_DRQ (data request),
where WDCS_DRQ = 0x8.  Is it possible that it's unnecessary to wait for
WDCS_DRQ in this case, where you're just setting a mode (ata_set_mode=0xc) and
not wanting to retrieve data from the platter?  I don't know anything about
ATA protocols, so I have no idea.  BTW: I haven't explicitly looked at the
values returned by ata_get_params in params.atap_piomode_supp and
params.atap_dmamode_supp; I should probably do that, but may not be able to
do it soon.

  The fact that it worked at full speed with dma under knoppix indicates that
it can be done.  The question is how difficult it is to fix, and whether it's
preferable just to buy a different card and hope it works better, i.e., that
it's a problem with support for the card and not a drive quirk.

--Jim