MIPS: Loongson 2F: Add CPU frequency scaling support

Loongson 2F supports CPU clock scaling. When put it into wait mode by
setting the frequency as ZERO it will stay in this mode until an external
interrupt wakes the CPU again.

To enable clock scaling support, an external timer of a known stable rate
is required.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: cpufreq@vger.kernel.org,
Cc: Dave Jones <davej@redhat.com>,
Cc: Dominik Brodowski <linux@dominikbrodowski.net>,
Cc: yanh@lemote.com
Cc: huhb@lemote.com,
Patchwork: http://patchwork.linux-mips.org/patch/660/
Patchwork: http://patchwork.linux-mips.org/patch/751/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson/common/platform.c

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2009 Lemote Inc.
+ * Author: Wu Zhangjin, wuzj@lemote.com
+ *
+ * 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/err.h>
+#include <linux/platform_device.h>
+
+static struct platform_device loongson2_cpufreq_device = {
+	.name = "loongson2_cpufreq",
+	.id = -1,
+};
+
+static int __init loongson2_cpufreq_init(void)
+{
+	struct cpuinfo_mips *c = &current_cpu_data;
+
+	/* Only 2F revision and it's successors support CPUFreq */
+	if ((c->processor_id & PRID_REV_MASK) >= PRID_REV_LOONGSON2F)
+		return platform_device_register(&loongson2_cpufreq_device);
+
+	return -ENODEV;
+}
+
+arch_initcall(loongson2_cpufreq_init);