kern/76893: Fatal divide in booting processes with Buslogic BT 958 FW SCSI disk controler.

[Andrew Bernard]

The following reply was made to PR kern/76893; it has been noted by GNATS.

From: "Andrew Bernard" <andrew at hobnob.com>
To: freebsd-gnats-submit at FreeBSD.org
Cc:  
Subject: Re: kern/76893: Fatal divide in booting processes with Buslogic BT 958 FW SCSI disk controler.
Date: 21 Mar 2005 17:44:04 -0500

 Hi,
 
 I've been having the same problem with FreeBSD 5.3 and my BT-958.
 
 It looks like the drive or the BT-958 is returning zero for its
 "period factor" for whatever reason.  The kernel code in
 src/sys/cam/scsi/scsi_all.c doesn't check for this (probably invalid)
 case and proceeds to use zero as a divisor at line 2329.
 
 Applying the following patch at line 2302 heads off the divide
 by zero and assumes that a "period factor" of zero means
 20 mbit/sec SCSI:
 
 2302c2302,2303
 <       { 0x0c, 5000 }  /* FAST-20 */
 ---
 >       { 0x0c, 5000 }, /* FAST-20 */
 >       { 0x00, 5000 }  /* FAST-20 */
 
 This enables the drive to come up normally.
 
 I've been using this patch on my home system for about a month
 now, with no apparent problems (but use at your own risk!).
 I don't know whether it's safe to assume FAST-20 when the
 BT-958 returns zero for its "period factor", but I think
 that the kernel should at least be checking for a zero divisor
 and reporting a device error (instead of bringing the whole
 system down on a zero divide fault).
 
 Please let me know if any additional information would be helpful.
 
 Thanks,
 
 Andrew Bernard