Re: [PARPORT] parport irq handler v7 test w/ 3 pp devices

David Campbell (
Thu, 24 Sep 1998 21:04:54 +0800

Date sent: Thu, 24 Sep 1998 12:44:46 +0200 (CEST)
From: Andrea Arcangeli <>
To: David Campbell <>
Copies to: Boszormenyi Zoltan <>,
Subject: Re: [PARPORT] parport irq handler v7 test w/ 3 pp devices

> On Mon, 21 Sep 1998, David Campbell wrote:
> >The ZIP drive has a minimum of a single timer tick before a request
> >is issued (due to SCSI pedantics - if I didn't wait a timer tick, a race
> >condition would occur resulting in the kernel about 200+ calls deep
> >and panic due to "out of stack space").
> That' s not a race condition. Is due how scsi code works. Every time you
> run scsi_done() inside the main ppa engine the scsi code will recall again
> the ppa engine:
> ppaengine -> scsi_done -> new scsi command ready -> ppa engine -> scsi_done
> If this would be done in the same stack without wait a bit between the two
> ppa engine this logic will overflow the kstack for sure (I experienced
> this many time in the past trying to make the ppa lighter and faster (and
> probably David remeber about that ;-)).

All too well... [ I need to check the definition of a "race condition" sometime]

> This bad behavior of the scsi code can' t be noticed with anything other
> ppa since all other driver are irq driven and so they never run
> scsi_done() from the same context that sent the scsi command to the scsi
> controller.

Only ppa and imm are SCSI devices, fortunately IDE does not have the
ability to queue commands at the hardware interface so the paride suite
is spared this horror.

David Campbell

Current project list:
a) Maintain Linux ZIP drivers
b) Create Linux chipset specific parport drivers
c) Start on ParSCSI drivers
d) Boot proms for parport devices (socket onto NE2000 cards)

Any assistance to clearing this list most welcome

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This archive was generated by hypermail 2.0b3 on Wed 30 Dec 1998 - 10:18:21 EST