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

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

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D56751

sys/powerpc/include/openpicvar.h

@@ -36,6 +36,7 @@
 
 #define	OPENPIC_QUIRK_SINGLE_BIND	1	/* Bind interrupts to only 1 CPU */
 #define	OPENPIC_QUIRK_HIDDEN_IRQS	2	/* May have IRQs beyond FRR[NIRQ] */
+#define	OPENPIC_QUIRK_WHOAMI_WORKS	4	/* WHOAMI register is present */
 
 /* Names match the macros in openpicreg.h. */
 struct openpic_timer {

sys/powerpc/ofw/openpic_ofw.c

@@ -125,6 +125,7 @@ openpic_ofw_attach(device_t dev)
 	if (ofw_bus_is_compatible(dev, "fsl,mpic")) {
 		sc->sc_quirks = OPENPIC_QUIRK_SINGLE_BIND;
 		sc->sc_quirks |= OPENPIC_QUIRK_HIDDEN_IRQS;
+		sc->sc_quirks |= OPENPIC_QUIRK_WHOAMI_WORKS;
 	}
 
 	return (openpic_common_attach(dev, xref));

sys/powerpc/powerpc/openpic.c

@@ -469,8 +469,23 @@ openpic_ap_init(device_t dev)
 	if (dev != root_pic)
 		return;
 
+	/*
+	 * Not everything implements the full OpenPIC specification.
+	 *
+	 * Notably the CPC945 Bridge and Memory Controller User Manual, which
+	 * is in the PPC 970 (ie Apple G5) CPUs, calls out a set of
+	 * deviations from the specification.  Thus we can't just assume
+	 * WHOAMI is available everywhere.
+	 *
+	 * See 9.5.3.3 - Deviations from the OpenPIC specification.
+	 * Notably - the WhoAmI register is actually 0xF8000050 for all CPUs.
+	 */
+
 	sc = device_get_softc(dev);
+	if (sc->sc_quirks & OPENPIC_QUIRK_WHOAMI_WORKS)
 		PCPU_SET(pic, bus_read_4(sc->sc_memr, OPENPIC_WHOAMI));
+	else
+		PCPU_SET(pic, PCPU_GET(cpuid));
 }
 
 static device_method_t openpic_methods[] = {