Re: esp_scsi, was Re: Modified Linux 4.1.20 (mac+scsi) on Quadra 660av

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Finn,

got sidetracked once again ...

>> Where? In esp_reconnect, we don't get to that point when returning from 
>> esp_reconnect_with_tag() after timeout.
> 
> Well, the point is, we potentially release ACK (either after the 
> Information Transfer command or after the Accept Message command) with ATN 
> still asserted.

Who asserts ATN in case of reselection? I always thought that the
target, by initiating reselection, assumes the role of initiator and is
in charge of driving bus phase changes (including control of ATN).

>> How does the target signal end of message in phase? Stop handshaking, or 
>> change phase?
> 
> Either would do. To stop handshaking would imply entering bus free phase.
> 
>> ATN going false?
> 
> AIUI, only the initiator can drive ATN.

So the initiator would have to read two tag message bytes if a target
reselects that had a tagged command disconnected? From the initiator
side, that should work (if an untagged commmand has been issued, no
tagged commands are sent so we expect either tagged or untagged
reselections).

>> With the DMA programmed for two tag bytes, and the reselection 
>> originating from a tagged command, I would expect the target to send the 
>> two tag bytes.
> 
> Sure, but I think the initator is messing it up along the way.

Can't see how - reconnect_with_tag() is only used if no untagged command
is on record for the target.

> 
>> Would it help to do the message transfer without DMA?
> 
> I would, just to see more clearly what was going on (command queue, 
> control lines, bus phase).

Not sure we can get control lines read - bus phases are available IIRC.

> Recall that Tuomas said he tried PIO for this with zorro_esp without any 
> improvement. And I first saw this bug on a Quadra 660av, on which mac_esp 
> uses PIO for all transfers.

PIO does get set up for the expected number of message bytes though. Is
there  a check for phase mismatch during PIO?

>>> What use could an initiator have for the QTAG Control bit 
>>> (ESP_CONFIG3_TBMS) when the target never controls /ATN? (I only 
>>> remembered this yesterday, so please ignore my earlier comments about 
>>> reselection and SEL-with-ATN.)
>>
>> I had thought the reselection process similar to selection. But if the 
>> target does not signal further message bytes by keepin ATN asserted, 
>> that bit might not matter here.
> 
> If only the initator drives ATN, the documentation can only be referring 
> to an ESP device in target mode.

The documentation mentions a command descriptor block to be transferred
- would only apply to ESP in target mode again.

> My recollection from 2009 is that this particular disk did work with 
> mac_esp on one of my Quadras, but not on my 660av. And three people have 
> reported the problem now (to my knowledge) so I don't blame the disks.

What ESP versions are used in the Quadras vs 660av?

Cheers,

	Michael