NetBSD Problem Report #60640

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Date: Tue, 25 Aug 2026 10:13:07 +0000 (UTC)
From: jack@zage.org.uk
Reply-To: jack@zage.org.uk
To: gnats-bugs@NetBSD.org
Subject: ofppc i8259 cascade interrupt wrong polarity.
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X-From4GNATS: "jack@zage.org.uk via gnats" <gnats-admin@NetBSD.org>

>Number:         60640
>Category:       port-ofppc
>Synopsis:       ofppc i8259 cascade interrupt wrong polarity.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-ofppc-maintainer
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Aug 25 10:15:00 +0000 2026
>Closed-Date:    Sat Oct 10 10:23:09 +0000 2026
>Last-Modified:  Sat Oct 10 10:23:09 +0000 2026
>Originator:     Jack Dunn
>Release:        current
>Organization:
>Environment:
NetBSD rs6000 11.99.7 NetBSD 11.99.7 (GENERIC) #9: Tue Aug 25 01:01:38 UTC 2026  jack@build:/home/jack/netbsd/obj/sys/arch/ofppc/compile/GENERIC ofppc

>Description:
On an ofppc machine which has a i8259 cascaded into an OpenPIC the kernel appears to hang shortly after autoconf. Holding a key down on the serial console makes forward progress. Investigation shows that pic_handle_intr() never leaves its pic_get_irq(PIC_GET_RECHECK) loop and the CPU spends 100% of its time in the interrupt handler.

The same issue occurs on two machines:
- Bull Escala T604e
- IBM RS/6000 7046 B50 / 7043 43p.

sys/arch/ofppc/ofppc/mainbus.c registers the i8259 cascade with IST_LEVEL. IST_LEVEL is an alias for IST_LEVEL_LOW but the i8259 is active high. 

Looks like opic_establish_irq() used to have a specical case which would handle this which was removed sometime around 2018 which caused the issue.

This issue only affects pic_openpic not pic_distopenpic or pic_mpcsoc.
>How-To-Repeat:
Boot ofppc on a machine with an OpenPIC/cascaded i8259. 
>Fix:
Change the line (sys/arch/ofppc/ofppc/mainbus.c)
intr_establish(16, IST_LEVEL, IPL_HIGH, pic_handle_intr, isa_pic);
to
intr_establish(16, IST_LEVEL_HIGH, IPL_HIGH, pic_handle_intr, isa_pic);

>Release-Note:

>Audit-Trail:
From: "Michael Lorenz" <macallan@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/60640 CVS commit: src/sys/arch/ofppc/ofppc
Date: Sat, 5 Sep 2026 10:24:03 +0000

 Module Name:	src
 Committed By:	macallan
 Date:		Sat Sep  5 10:24:03 UTC 2026

 Modified Files:
 	src/sys/arch/ofppc/ofppc: mainbus.c

 Log Message:
 register cascaded interrupt with correct polarity
 from PR60640
 Thanks!


 To generate a diff of this commit:
 cvs rdiff -u -r1.33 -r1.34 src/sys/arch/ofppc/ofppc/mainbus.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->closed
State-Changed-By: macallan@NetBSD.org
State-Changed-When: Sat, 10 Oct 2026 10:23:09 +0000
State-Changed-Why:
fix has been committed and confirmed working on my 43P-150


>Unformatted:

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