x86: apic: Fix mismerge, add arch_probe_nr_irqs() again

Merge commit aef55d4 mis-merged io_apic.c so we lost the
arch_probe_nr_irqs() method.

This caused subtle boot breakages (udev confusion likely
due to missing drivers) with certain configs.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20100207210250.GB8256@jenkins.home.ifup.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/apic/io_apic.c

@@ -3876,6 +3876,28 @@ void __init probe_nr_irqs_gsi(void)
 	printk(KERN_DEBUG "nr_irqs_gsi: %d\n", nr_irqs_gsi);
 }
 
+#ifdef CONFIG_SPARSE_IRQ
+int __init arch_probe_nr_irqs(void)
+{
+	int nr;
+
+	if (nr_irqs > (NR_VECTORS * nr_cpu_ids))
+		nr_irqs = NR_VECTORS * nr_cpu_ids;
+
+	nr = nr_irqs_gsi + 8 * nr_cpu_ids;
+#if defined(CONFIG_PCI_MSI) || defined(CONFIG_HT_IRQ)
+	/*
+	 * for MSI and HT dyn irq
+	 */
+	nr += nr_irqs_gsi * 16;
+#endif
+	if (nr < nr_irqs)
+		nr_irqs = nr;
+
+	return 0;
+}
+#endif
+
 static int __io_apic_set_pci_routing(struct device *dev, int irq,
 				struct io_apic_irq_attr *irq_attr)
 {