What is an "Unexpected Busfree"?

[Tom Wirschell]

On Thu, 01 Mar 2001 09:26:37 Doug Ledford wrote:
> 
> This is a slightly older version of my driver.  You can try using either
> my updated driver (which I think is already in 2.4.2, but you can check
> to make sure as the latest 2.4 kernel version of my driver is 5.2.3),
> or you can try Justin's latest driver and see if one of the two (or
> both) will solve your problem.

I started with Justin's driver, but it's using a constant (I'm really
sorry, but I can't remember which one. Just unpack the files into your
Linux 2.4.2 source tree, compile and you'll see) which isn't defined
anywhere.
Next option was to patch the kernel so that I'd use this 5.2.3 version of
the driver. Since it cleanly applied against 2.4.1 (there were some rejects
with 2.4.2) I used this combination and sure enough it improved my
situation in certain areas considerably, but unfortunately it did not
remove the problem and it introduced a new one.

I was able to scan 52 pages when the thing blocked and I had to wait 60
seconds or so for the reset. This time the driver was slightly more vocal
about what was happening:

Mar  3 14:43:34 LEV8 kernel: scsi : aborting command due to timeout : pid
0, scsi0, channel 0, id 0, lun 0 0x2a 00 00 4b 60 a0 00 00 08 00
Mar  3 14:43:34 LEV8 kernel: (scsi0:0:0:0) SCSISIGI 0x14, SEQADDR 0x4e,
SSTAT0 0x0, SSTAT1 0x13
Mar  3 14:43:34 LEV8 kernel: (scsi0:0:0:0) SG_CACHEPTR 0x2, SSTAT2 0x0,
STCNT 0x0
Mar  3 14:43:34 LEV8 kernel: scsi : aborting command due to timeout : pid
0, scsi0, channel 0, id 0, lun 0 0x2a 00 00 3f 62 a0 00 00 08 00
Mar  3 14:43:34 LEV8 kernel: scsi : aborting command due to timeout : pid
0, scsi0, channel 0, id 0, lun 0 0x2a 00 00 3f 62 28 00 00 08 00
Mar  3 14:43:34 LEV8 kernel: SCSI host 0 abort (pid 0) timed out -
resetting
Mar  3 14:43:34 LEV8 kernel: SCSI bus is being reset for host 0 channel 0.
Mar  3 14:43:34 LEV8 kernel: (scsi0:0:0:0) Synchronous at 80.0 Mbyte/sec,
offset 63.

After the reset it wasn't long until the "Unexpected busfree" messages came
popping up again:

Mar  3 14:45:34 LEV8 kernel: (scsi0:0:3:-1) Unexpected busfree, LASTPHASE =
0x1, SEQADDR = 0x167

Biggest difference with the old driver was that the above messages didn't
result in a 10-second pause, but at most a 1 second pause which even though
still annoying is a *LOT* more acceptable.

I went on to make another 100 or so scans and never got a reoccurrance of
the lockup of the SCSI-bus followed by a reset, but the "Unexpected
busfree" messages appeared pretty much continuously.

Now I knew that, at least with the old driver, once the 'busfree' messages
started, my SCSI bus would somehow be in a weird state that made other
devices on the SCSI chain act strange. Previously this meant that if I were
to for instance burn a CD with cdrecord, the burn would never start because
of 'incorrect sense data' or something similar. The way to make sure you
would be able to burn again was to simply mount a cd in the drive, as this
would result in another SCSI-bus lock up, followed by a reset. After the
reset, burning was once again possible. Same deal with playing DVD's. Until
you managed to get the SCSI-bus to reset once the 'busfree' messages began
to flow, DVD-playback would either fail completely or be extremely choppy.
After the reset everything would be smooth as silk.

This is the area where the current driver introduced a new 'problem'.
I have gotten the reset, was getting 'Unexpected busfree' errors, stopped
scanning and decided to play a dvd, started the player and it failed. I
then mounted the DVD which previously resulted in a reset, but with this
new driver the mounting worked flawlessly. Since the bus didn't reset, I
was unable to play any DVD's until I rebooted the machine. Note that I
forgot to try playing a DVD by simply telling it to play the .vob file on
the now mounted DVD. Instead I let XINE access the DVD-drive directly which
is the normal way of playing. Listings of the files on the mounted DVD
looked fine though.

I'm hoping someone out there will once again be able to give me some good
advice on how to tackle these problems. If there are anyquestions, feel
free to ask.

Sincerely,

Tom Wirschell
-- 
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