diff --git a/src/southbridge/intel/bd82x6x/early_rcba.c b/src/southbridge/intel/bd82x6x/early_rcba.c
index 443b6c20bf..0dd7a562b1 100644
--- a/src/southbridge/intel/bd82x6x/early_rcba.c
+++ b/src/southbridge/intel/bd82x6x/early_rcba.c
@@ -23,40 +23,73 @@ void
 southbridge_configure_default_intmap(void)
 {
 	/*
-	 *             GFX    INTA -> PIRQA (MSI)
-	 * D28IP_P1IP  SLOT1  INTA -> PIRQB
-	 * D28IP_P2IP  SLOT2  INTB -> PIRQF
-	 * D28IP_P3IP  SLOT3  INTC -> PIRQD
-	 * D28IP_P5IP  SLOT5  INTC -> PIRQD
-	 * D29IP_E1P   EHCI1  INTA -> PIRQD
-	 * D26IP_E2P   EHCI2  INTA -> PIRQF
-	 * D31IP_SIP   SATA   INTA -> PIRQB (MSI)
-	 * D31IP_SMIP  SMBUS  INTB -> PIRQH
-	 * D31IP_TTIP  THRT   INTC -> PIRQA
-	 * D27IP_ZIP   HDA    INTA -> PIRQA (MSI)
-	 *
-
+	 * For the PCH internal PCI functions, provide a reasonable
+	 * default IRQ mapping that utilizes only PIRQ A to D. Higher
+	 * PIRQs are sometimes used for other on-board chips that
+	 * require an edge triggered interrupt which is not shareable.
 	 */
 
-	RCBA32(D31IP) = (INTC << D31IP_TTIP) | (NOINT << D31IP_SIP2) |
+	/*
+	 * We use a linear mapping for the pin numbers. They are not
+	 * physical pins, and thus, have no relation between the dif-
+	 * ferent devices. Only rule we must obey is that a single-
+	 * function device has to use pin A.
+	 */
+	RCBA32(D31IP) = (INTD << D31IP_TTIP) | (INTC << D31IP_SIP2) |
 			(INTB << D31IP_SMIP) | (INTA << D31IP_SIP);
-	RCBA32(D30IP) = (NOINT << D30IP_PIP);
 	RCBA32(D29IP) = (INTA << D29IP_E1P);
-	RCBA32(D28IP) = (INTA << D28IP_P1IP) | (INTB << D28IP_P2IP) |
-			(INTC << D28IP_P3IP) | (INTC << D28IP_P5IP);
+	RCBA32(D28IP) = (INTD << D28IP_P8IP) | (INTC << D28IP_P7IP) |
+			(INTB << D28IP_P6IP) | (INTA << D28IP_P5IP) |
+			(INTD << D28IP_P4IP) | (INTC << D28IP_P3IP) |
+			(INTB << D28IP_P2IP) | (INTA << D28IP_P1IP);
 	RCBA32(D27IP) = (INTA << D27IP_ZIP);
 	RCBA32(D26IP) = (INTA << D26IP_E2P);
-	RCBA32(D25IP) = (NOINT << D25IP_LIP);
-	RCBA32(D22IP) = (NOINT << D22IP_MEI1IP);
+	RCBA32(D25IP) = (INTA << D25IP_LIP);
+	RCBA32(D22IP) = (INTA << D22IP_MEI1IP);
+	RCBA32(D20IP) = (INTA << D20IP_XHCIIP);
 
-	/* Device interrupt route registers */
-	DIR_ROUTE(D31IR, PIRQB, PIRQH, PIRQA, PIRQC);
-	DIR_ROUTE(D29IR, PIRQD, PIRQE, PIRQF, PIRQG);
-	DIR_ROUTE(D28IR, PIRQB, PIRQF, PIRQD, PIRQE);
-	DIR_ROUTE(D27IR, PIRQA, PIRQH, PIRQA, PIRQB);
-	DIR_ROUTE(D26IR, PIRQF, PIRQE, PIRQG, PIRQH);
-	DIR_ROUTE(D25IR, PIRQA, PIRQB, PIRQC, PIRQD);
-	DIR_ROUTE(D22IR, PIRQA, PIRQB, PIRQC, PIRQD);
+	/*
+	 * For the PIRQ allocation the following was taken into
+	 * account:
+	 *   o Interrupts of the PCIe root ports are only about
+	 *     events at the ports, not downstream devices. So we
+	 *     don't expect many interrupts there and ignore them.
+	 *   o We don't expect to talk constantly to the ME either
+	 *     so ignore that, too. Same for SMBus and the thermal
+	 *     device.
+	 *   o Second SATA interface is only used in non-AHCI mode
+	 *     so unlikely to coexist with modern interfaces (e.g.
+	 *     xHCI).
+	 *   o An OS that knows USB3 will likely also know how to
+	 *     use MSI.
+	 *
+	 * The functions that might matter first:
+	 *
+	 * D31IP_SIP	SATA 1	-> PIRQ A (MSI capable in AHCI mode)
+	 * D31IP_SIP2	SATA 2	-> PIRQ B
+	 * D29IP_E1P	EHCI 1	-> PIRQ C
+	 * D27IP_ZIP	HDA	-> PIRQ D (MSI capable)
+	 * D26IP_E2P	EHCI 2	-> PIRQ D
+	 * D25IP_LIP	GbE	-> PIRQ B (MSI capable)
+	 * D20IP_XHCIIP	xHCI	-> PIRQ B (MSI capable)
+	 *
+	 * D31IP_TTIP	Thermal	-> PIRQ B
+	 * D31IP_SMIP	SMBUS	-> PIRQ A
+	 * D28IP_*	PCIe RP	-> PIRQ A-D (MSI capable)
+	 * D22IP_MEI1IP	ME	-> PIRQ A (MSI capable)
+	 *
+	 * Note, CPU-integrated functions seem to always use PIRQ A.
+	 */
+#define _none 0
+	DIR_ROUTE(D31IR, PIRQA, PIRQA, PIRQB, PIRQB);
+	DIR_ROUTE(D29IR, PIRQC, _none, _none, _none);
+	DIR_ROUTE(D28IR, PIRQA, PIRQB, PIRQC, PIRQD);
+	DIR_ROUTE(D27IR, PIRQD, _none, _none, _none);
+	DIR_ROUTE(D26IR, PIRQD, _none, _none, _none);
+	DIR_ROUTE(D25IR, PIRQB, _none, _none, _none);
+	DIR_ROUTE(D22IR, PIRQA, _none, _none, _none);
+	DIR_ROUTE(D20IR, PIRQB, _none, _none, _none);
+#undef _none
 
 	/* Enable IOAPIC (generic) */
 	RCBA16(OIC) = 0x0100;