powerpc: Add support for using doorbells for SMP IPI

The e500mc supports the new msgsnd/doorbell mechanisms that were added in
the Power ISA 2.05 architecture.  We use the normal level doorbell for
doing SMP IPIs at this point.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/dbell.c

@@ -0,0 +1,44 @@
+/*
+ * Author: Kumar Gala <galak@kernel.crashing.org>
+ *
+ * Copyright 2009 Freescale Semiconductor Inc.
+ *
+ * This program is free software; you can redistribute  it and/or modify it
+ * under  the terms of  the GNU General  Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ */
+
+#include <linux/stddef.h>
+#include <linux/kernel.h>
+#include <linux/smp.h>
+#include <linux/threads.h>
+
+#include <asm/dbell.h>
+
+#ifdef CONFIG_SMP
+unsigned long dbell_smp_message[NR_CPUS];
+
+void smp_dbell_message_pass(int target, int msg)
+{
+	int i;
+
+	if(target < NR_CPUS) {
+		set_bit(msg, &dbell_smp_message[target]);
+		ppc_msgsnd(PPC_DBELL, 0, target);
+	}
+	else if(target == MSG_ALL_BUT_SELF) {
+		for_each_online_cpu(i) {
+			if (i == smp_processor_id())
+				continue;
+			set_bit(msg, &dbell_smp_message[i]);
+			ppc_msgsnd(PPC_DBELL, 0, i);
+		}
+	}
+	else { /* target == MSG_ALL */
+		for_each_online_cpu(i)
+			set_bit(msg, &dbell_smp_message[i]);
+		ppc_msgsnd(PPC_DBELL, PPC_DBELL_MSG_BRDCAST, 0);
+	}
+}
+#endif