Re: [PATCH 1/4] aic79xx: Fixup external device reset

[Hannes Reinecke <hare@suse.de>]

James Bottomley wrote:
> On Mon, 2006-10-23 at 15:22 +0200, Hannes Reinecke wrote:
>> +                       /* Hand-craft TUR command */
>> +                       ahd_outb(ahd, SCB_CDB_STORE, 0);
>> +                       ahd_outb(ahd, SCB_CDB_STORE+1, 0);
>> +                       ahd_outb(ahd, SCB_CDB_STORE+2, 0);
>> +                       ahd_outb(ahd, SCB_CDB_STORE+3, 0);
>> +                       ahd_outb(ahd, SCB_CDB_STORE+4, 0);
>> +                       ahd_outb(ahd, SCB_CDB_STORE+5, 0);
>> +                       ahd_outb(ahd, SCB_CDB_LEN, 6);
>> +                       scb->hscb->control &= ~(TAG_ENB|SCB_TAG_TYPE);
>> +                       scb->hscb->control |= MK_MESSAGE;
>> +                       ahd_outb(ahd, SCB_CONTROL, scb->hscb->control);
>> +                       ahd_outb(ahd, MSG_OUT, HOST_MSG);
>> +                       ahd_outb(ahd, SAVED_SCSIID, scb->hscb->scsiid);
> 
> What's the reason for having to have this hand crafted test unit ready?
> 
I asked myself the same question. It's actually from the original 
adaptec sources, and i couldn't figure out why it was need, either.
That's why I removed it initially when doing the first round of external 
device reset patches.

Thing is whenever we send a SCB with the MK_MESSAGE flag set the 
sequencer will interrupt normal SCB delivery and ensure that the 
MK_MESSAGE SCB is sent immediately. Plus we can force the connection to 
non-packetized transfer as the resetted target will start out with 
normal transfers, too. And as we already have invalidated the 
negotiation settings for all targets a renegotiation will happen when 
this TUR is completed.
So the normal flow of operation can continue and only one command will 
have to be requeued from the midlayer.

I think. Or that's what I've glanced from the sequencer code. Maybe Rob 
can give some more insight here.

Admittedly, this is really a nasty tweaking. In theory we should have a 
proper error handler which handles this sort of thing. But the entire 
code is littered with such tweakings so that's quite a vain hope.
Unless someone passes me a theory of operation document for it.
Having a register description is quite pointless.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux Products GmbH		S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de
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