PCI: do not route nonexistent PIRQs on ALI M1533/1543 IRQ router

Some BIOS versions have link numbers 5..8 in PIRQ routing tables for
ALI M1533, but the chip is configured for 4 PIRQ inputs.  Attempts to
configure these nonexistent PIRQs result in screaming IRQs.

This patch disables PIRQ routing for links 5..8 if the chip is not
configured for 8 PIRQ inputs.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>

---

 arch/i386/pci/irq.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 38 insertions(+), 0 deletions(-)

2a4412ddbbfb3a231af17dfffbb7b09abf79a2e0
diff --git a/arch/i386/pci/irq.c b/arch/i386/pci/irq.c
index 3ca59ca..aa768fa 100644
--- a/arch/i386/pci/irq.c
+++ b/arch/i386/pci/irq.c
@@ -216,6 +216,38 @@ static int pirq_ali_set(struct pci_dev *
 }
 
 /*
+ * ALI M1533/1543 can support either 4 or 8 PIRQ inputs.  Trying to
+ * route PIRQs 5..8 when using 4 PIRQ inputs results in screaming IRQs.
+ * Of course, some BIOS versions have bogus PIRQ table entries.
+ */
+static int pirq_ali_m1533_is_valid(struct pci_dev *router, int pirq)
+{
+	if ((pirq >= 5) && (pirq <= 8)) {
+		u8 reg45;
+		pci_read_config_byte(router, 0x45, &reg45);
+		if (!(reg45 & 0x80))
+			return 0;
+	}
+	return 1;
+}
+
+static int pirq_ali_m1533_get(struct pci_dev *router, struct pci_dev *dev,
+			      int pirq)
+{
+	if (!pirq_ali_m1533_is_valid(router, pirq))
+		return 0;
+	return pirq_ali_get(router, dev, pirq);
+}
+
+static int pirq_ali_m1533_set(struct pci_dev *router, struct pci_dev *dev,
+			      int pirq, int irq)
+{
+	if (!pirq_ali_m1533_is_valid(router, pirq))
+		return 0;
+	return pirq_ali_set(router, dev, pirq, irq);
+}
+
+/*
  * The Intel PIIX4 pirq rules are fairly simple: "pirq" is
  * just a pointer to the config space.
  */
@@ -681,6 +713,12 @@ static __init int ali_router_probe(struc
 	switch(device)
 	{
 	case PCI_DEVICE_ID_AL_M1533:
+		printk(KERN_DEBUG "PCI: Using ALI M1533 IRQ Router\n");
+		r->name = "ALI M1533";
+		r->get = pirq_ali_m1533_get;
+		r->set = pirq_ali_m1533_set;
+		return 1;
+
 	case PCI_DEVICE_ID_AL_M1563:
 		printk(KERN_DEBUG "PCI: Using ALI IRQ Router\n");
 		r->name = "ALI";