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>Number: 60640
>Category: port-ofppc
>Synopsis: ofppc i8259 cascade interrupt wrong polarity.
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: port-ofppc-maintainer
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Tue Aug 25 10:15:00 +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);