Re: Serverworks OSB4 in impossible state

From: Martin Wilck (
Date: Tue Jun 11 2002 - 02:22:24 EST

Am Mon, 2002-06-10 um 18.41 schrieb Daniela Engert:

> The intersting bits of the DMA status register are bits 0 though 2. A
> value of 5 indicates the condition "interrupt from unit, DMA state
> machine active". This is a valid status! It basically means the unit
> issued an interrupt before the PRD table is exhausted. This makes sense
> because the CD-ROM units fails to transfer the amount of data described
> by the PRD table because of the non-recoverable read error.

Shouldn't the error bit be set too? (But that wouldn't make any
difference with the current driver ...)

> What you makes sense (the next DMA transfer is scheduled but never
> carried out by the CD-ROM unit) except for the panic, ofcoz. The
> correct driver action in this case were stopping the DMA engine and
> issuing a reset of the state machines involved (both on the host and
> the unit side).

The message, the comments in the code, and what Alan wrote here:
suggest that trying to recover from this condition is extremely
dangerous (note that the kernel doesn't even panic(), because
a sync() may kill a disk, the comments say).

Anyway, thanks a lot for your insightful comments.

Martin Wilck                Phone: +49 5251 8 15113
Fujitsu Siemens Computers   Fax:   +49 5251 8 20409
Heinz-Nixdorf-Ring 1
D-33106 Paderborn 

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