Differential D56751

powerpc/pic: fix the openpic CPU logic to work on powermac
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Authored by adrian on Apr 30 2026, 7:50 PM.

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rG6a0610cb5018: powerpc/pic: fix the openpic CPU logic to work on powermac

Summary

Earlier work (40bcad56f - powerpc/pic: Add a PIC_AP_INIT() to
set up AP PIC info) broke booting my dual G5 powermac.

After much digging, jhibbits@ and I discovered that the openpic
implementation for the memory/bus controller used in the G5 CPUs
doesn't implement /all/ of the openpic specification.
Notably it sticks the WHOAMI register in a different location.
This is reading 0x0 back for all the PICs which is .. very not great.

So to restore the previous behaviour, use a quick for now that jhibbits@
can set appropriately to trust WHOAMI.

I've tested this on my dual G5 PPC and it boots/runs fine.

Fixes: 40bcad56f

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rG FreeBSD src repository

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Event Timeline

adrian created this revision.Apr 30 2026, 7:50 PM

Herald added subscribers: jhibbits, imp. · View Herald TranscriptApr 30 2026, 7:50 PM

adrian requested review of this revision.Apr 30 2026, 7:50 PM

Harbormaster completed remote builds in B72685: Diff 176947.Apr 30 2026, 7:50 PM

adrian added a project: PowerPC.Apr 30 2026, 7:51 PM

adrian added reviewers: PowerPC, jhibbits.

Herald added subscribers: alfredo, luporl, bdragon. · View Herald TranscriptApr 30 2026, 7:51 PM

update

Harbormaster completed remote builds in B72686: Diff 176953.Apr 30 2026, 9:01 PM

This really is funny, that we're working around broken IBM and Apple hardware by putting a quirk on the one conforming implementer.

This revision is now accepted and ready to land.Apr 30 2026, 10:24 PM

Closed by commit rG6a0610cb5018: powerpc/pic: fix the openpic CPU logic to work on powermac (authored by adrian). · Explain WhyMay 1 2026, 12:08 AM

This revision was automatically updated to reflect the committed changes.

adrian added a commit: rG6a0610cb5018: powerpc/pic: fix the openpic CPU logic to work on powermac.

Revision Contents
Changeset List

Path

Size

sys/

powerpc/

include/

1 line

ofw/

1 line

powerpc/

17 lines

Diff 176969

sys/powerpc/include/openpicvar.h

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sys/powerpc/ofw/openpic_ofw.c

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sys/powerpc/powerpc/openpic.c

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