port-ofppc/60640: ofppc i8259 cascade interrupt wrong polarity.

["jack%zage.org.uk@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>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);