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>

13 files changed, 524 insertions, 4 deletions

diff --git a/arch/mips/include/asm/clock.h b/arch/mips/include/asm/clock.h
new file mode 100644
index 000000000000..83894aa7932c
--- /dev/null
+++ b/arch/mips/include/asm/clock.h
@@ -0,0 +1,64 @@
+#ifndef __ASM_MIPS_CLOCK_H
+#define __ASM_MIPS_CLOCK_H
+
+#include <linux/kref.h>
+#include <linux/list.h>
+#include <linux/seq_file.h>
+#include <linux/clk.h>
+
+extern void (*cpu_wait) (void);
+
+struct clk;
+
+struct clk_ops {
+	void (*init) (struct clk *clk);
+	void (*enable) (struct clk *clk);
+	void (*disable) (struct clk *clk);
+	void (*recalc) (struct clk *clk);
+	int (*set_rate) (struct clk *clk, unsigned long rate, int algo_id);
+	long (*round_rate) (struct clk *clk, unsigned long rate);
+};
+
+struct clk {
+	struct list_head node;
+	const char *name;
+	int id;
+	struct module *owner;
+
+	struct clk *parent;
+	struct clk_ops *ops;
+
+	struct kref kref;
+
+	unsigned long rate;
+	unsigned long flags;
+};
+
+#define CLK_ALWAYS_ENABLED	(1 << 0)
+#define CLK_RATE_PROPAGATES	(1 << 1)
+
+/* Should be defined by processor-specific code */
+void arch_init_clk_ops(struct clk_ops **, int type);
+
+int clk_init(void);
+
+int __clk_enable(struct clk *);
+void __clk_disable(struct clk *);
+
+void clk_recalc_rate(struct clk *);
+
+int clk_register(struct clk *);
+void clk_unregister(struct clk *);
+
+/* the exported API, in addition to clk_set_rate */
+/**
+ * clk_set_rate_ex - set the clock rate for a clock source, with additional parameter
+ * @clk: clock source
+ * @rate: desired clock rate in Hz
+ * @algo_id: algorithm id to be passed down to ops->set_rate
+ *
+ * Returns success (0) or negative errno.
+ */
+int clk_set_rate_ex(struct clk *clk, unsigned long rate, int algo_id);
+
+#endif				/* __ASM_MIPS_CLOCK_H */
diff --git a/arch/mips/include/asm/cpu.h b/arch/mips/include/asm/cpu.h
index 4b96d1a36056..cf373a95fe4a 100644
--- a/arch/mips/include/asm/cpu.h
+++ b/arch/mips/include/asm/cpu.h
@@ -154,6 +154,8 @@
 #define PRID_REV_VR4181A	0x0070	/* Same as VR4122 */
 #define PRID_REV_VR4130		0x0080
 #define PRID_REV_34K_V1_0_2	0x0022
+#define PRID_REV_LOONGSON2E	0x0002
+#define PRID_REV_LOONGSON2F	0x0003
 
 /*
  * Older processors used to encode processor version and revision in two
diff --git a/arch/mips/include/asm/mach-loongson/loongson.h b/arch/mips/include/asm/mach-loongson/loongson.h
index 9bccdb5d4b51..a7fa66e85988 100644
--- a/arch/mips/include/asm/mach-loongson/loongson.h
+++ b/arch/mips/include/asm/mach-loongson/loongson.h
@@ -226,8 +226,12 @@ extern void mach_irq_dispatch(unsigned int pending);
 #define LOONGSON_PCIMAP_WIN(WIN, ADDR)	\
 	((((ADDR)>>26) & LOONGSON_PCIMAP_PCIMAP_LO0) << ((WIN)*6))
 
-/* Chip Config */
 #ifdef CONFIG_CPU_SUPPORTS_CPUFREQ
+#include <linux/cpufreq.h>
+extern void loongson2_cpu_wait(void);
+extern struct cpufreq_frequency_table loongson2_clockmod_table[];
+
+/* Chip Config */
 #define LOONGSON_CHIPCFG0		LOONGSON_REG(LOONGSON_REGBASE + 0x80)
 #endif
 
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index a446aa20ac83..f442de804d8a 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -93,4 +93,6 @@ CFLAGS_cpu-bugs64.o	= $(shell if $(CC) $(KBUILD_CFLAGS) -Wa,-mdaddi -c -o /dev/n
 
 obj-$(CONFIG_HAVE_STD_PC_SERIAL_PORT)	+= 8250-platform.o
 
+obj-$(CONFIG_MIPS_CPUFREQ)	+= cpufreq/
+
 EXTRA_CFLAGS += -Werror
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 7a51866068a4..80e202eca056 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -16,6 +16,7 @@
 #include <linux/ptrace.h>
 #include <linux/smp.h>
 #include <linux/stddef.h>
+#include <linux/module.h>
 
 #include <asm/bugs.h>
 #include <asm/cpu.h>
@@ -32,6 +33,7 @@
  * the CPU very much.
  */
 void (*cpu_wait)(void);
+EXPORT_SYMBOL(cpu_wait);
 
 static void r3081_wait(void)
 {
diff --git a/arch/mips/kernel/cpufreq/Kconfig b/arch/mips/kernel/cpufreq/Kconfig
index 37983a15dabe..58c601eee6fd 100644
--- a/arch/mips/kernel/cpufreq/Kconfig
+++ b/arch/mips/kernel/cpufreq/Kconfig
@@ -20,6 +20,20 @@ if CPU_FREQ
 
 comment "CPUFreq processor drivers"
 
+config LOONGSON2_CPUFREQ
+	tristate "Loongson2 CPUFreq Driver"
+	select CPU_FREQ_TABLE
+	depends on MIPS_CPUFREQ
+	help
+	  This option adds a CPUFreq driver for loongson processors which
+	  support software configurable cpu frequency.
+
+	  Loongson2F and it's successors support this feature.
+
+	  For details, take a look at <file:Documentation/cpu-freq/>.
+
+	  If in doubt, say N.
+
 endif	# CPU_FREQ
 
 endmenu
diff --git a/arch/mips/kernel/cpufreq/Makefile b/arch/mips/kernel/cpufreq/Makefile
new file mode 100644
index 000000000000..c3479a432efe
--- /dev/null
+++ b/arch/mips/kernel/cpufreq/Makefile
@@ -0,0 +1,5 @@
+#
+# Makefile for the Linux/MIPS cpufreq.
+#
+
+obj-$(CONFIG_LOONGSON2_CPUFREQ) += loongson2_cpufreq.o loongson2_clock.o
diff --git a/arch/mips/kernel/cpufreq/loongson2_clock.c b/arch/mips/kernel/cpufreq/loongson2_clock.c
new file mode 100644
index 000000000000..d7ca256e33ef
--- /dev/null
+++ b/arch/mips/kernel/cpufreq/loongson2_clock.c
@@ -0,0 +1,166 @@
+/*
+ * Copyright (C) 2006 - 2008 Lemote Inc. & Insititute of Computing Technology
+ * Author: Yanhua, yanh@lemote.com
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/cpufreq.h>
+#include <linux/platform_device.h>
+
+#include <asm/clock.h>
+
+#include <loongson.h>
+
+static LIST_HEAD(clock_list);
+static DEFINE_SPINLOCK(clock_lock);
+static DEFINE_MUTEX(clock_list_sem);
+
+/* Minimum CLK support */
+enum {
+	DC_ZERO, DC_25PT = 2, DC_37PT, DC_50PT, DC_62PT, DC_75PT,
+	DC_87PT, DC_DISABLE, DC_RESV
+};
+
+struct cpufreq_frequency_table loongson2_clockmod_table[] = {
+	{DC_RESV, CPUFREQ_ENTRY_INVALID},
+	{DC_ZERO, CPUFREQ_ENTRY_INVALID},
+	{DC_25PT, 0},
+	{DC_37PT, 0},
+	{DC_50PT, 0},
+	{DC_62PT, 0},
+	{DC_75PT, 0},
+	{DC_87PT, 0},
+	{DC_DISABLE, 0},
+	{DC_RESV, CPUFREQ_TABLE_END},
+};
+EXPORT_SYMBOL_GPL(loongson2_clockmod_table);
+
+static struct clk cpu_clk = {
+	.name = "cpu_clk",
+	.flags = CLK_ALWAYS_ENABLED | CLK_RATE_PROPAGATES,
+	.rate = 800000000,
+};
+
+struct clk *clk_get(struct device *dev, const char *id)
+{
+	return &cpu_clk;
+}
+EXPORT_SYMBOL(clk_get);
+
+static void propagate_rate(struct clk *clk)
+{
+	struct clk *clkp;
+
+	list_for_each_entry(clkp, &clock_list, node) {
+		if (likely(clkp->parent != clk))
+			continue;
+		if (likely(clkp->ops && clkp->ops->recalc))
+			clkp->ops->recalc(clkp);
+		if (unlikely(clkp->flags & CLK_RATE_PROPAGATES))
+			propagate_rate(clkp);
+	}
+}
+
+int clk_enable(struct clk *clk)
+{
+	return 0;
+}
+EXPORT_SYMBOL(clk_enable);
+
+void clk_disable(struct clk *clk)
+{
+}
+EXPORT_SYMBOL(clk_disable);
+
+unsigned long clk_get_rate(struct clk *clk)
+{
+	return (unsigned long)clk->rate;
+}
+EXPORT_SYMBOL(clk_get_rate);
+
+void clk_put(struct clk *clk)
+{
+}
+EXPORT_SYMBOL(clk_put);
+
+int clk_set_rate(struct clk *clk, unsigned long rate)
+{
+	return clk_set_rate_ex(clk, rate, 0);
+}
+EXPORT_SYMBOL_GPL(clk_set_rate);
+
+int clk_set_rate_ex(struct clk *clk, unsigned long rate, int algo_id)
+{
+	int ret = 0;
+	int regval;
+	int i;
+
+	if (likely(clk->ops && clk->ops->set_rate)) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&clock_lock, flags);
+		ret = clk->ops->set_rate(clk, rate, algo_id);
+		spin_unlock_irqrestore(&clock_lock, flags);
+	}
+
+	if (unlikely(clk->flags & CLK_RATE_PROPAGATES))
+		propagate_rate(clk);
+
+	for (i = 0; loongson2_clockmod_table[i].frequency != CPUFREQ_TABLE_END;
+	     i++) {
+		if (loongson2_clockmod_table[i].frequency ==
+		    CPUFREQ_ENTRY_INVALID)
+			continue;
+		if (rate == loongson2_clockmod_table[i].frequency)
+			break;
+	}
+	if (rate != loongson2_clockmod_table[i].frequency)
+		return -ENOTSUPP;
+
+	clk->rate = rate;
+
+	regval = LOONGSON_CHIPCFG0;
+	regval = (regval & ~0x7) | (loongson2_clockmod_table[i].index - 1);
+	LOONGSON_CHIPCFG0 = regval;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_set_rate_ex);
+
+long clk_round_rate(struct clk *clk, unsigned long rate)
+{
+	if (likely(clk->ops && clk->ops->round_rate)) {
+		unsigned long flags, rounded;
+
+		spin_lock_irqsave(&clock_lock, flags);
+		rounded = clk->ops->round_rate(clk, rate);
+		spin_unlock_irqrestore(&clock_lock, flags);
+
+		return rounded;
+	}
+
+	return rate;
+}
+EXPORT_SYMBOL_GPL(clk_round_rate);
+
+/*
+ * This is the simple version of Loongson-2 wait, Maybe we need do this in
+ * interrupt disabled content
+ */
+
+DEFINE_SPINLOCK(loongson2_wait_lock);
+void loongson2_cpu_wait(void)
+{
+	u32 cpu_freq;
+	unsigned long flags;
+
+	spin_lock_irqsave(&loongson2_wait_lock, flags);
+	cpu_freq = LOONGSON_CHIPCFG0;
+	LOONGSON_CHIPCFG0 &= ~0x7;	/* Put CPU into wait mode */
+	LOONGSON_CHIPCFG0 = cpu_freq;	/* Restore CPU state */
+	spin_unlock_irqrestore(&loongson2_wait_lock, flags);
+}
+EXPORT_SYMBOL_GPL(loongson2_cpu_wait);
diff --git a/arch/mips/kernel/cpufreq/loongson2_cpufreq.c b/arch/mips/kernel/cpufreq/loongson2_cpufreq.c
new file mode 100644
index 000000000000..2f6a0b147ab8
--- /dev/null
+++ b/arch/mips/kernel/cpufreq/loongson2_cpufreq.c
@@ -0,0 +1,227 @@
+/*
+ * Cpufreq driver for the loongson-2 processors
+ *
+ * The 2E revision of loongson processor not support this feature.
+ *
+ * Copyright (C) 2006 - 2008 Lemote Inc. & Insititute of Computing Technology
+ * Author: Yanhua, yanh@lemote.com
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+#include <linux/cpufreq.h>
+#include <linux/module.h>
+#include <linux/err.h>
+#include <linux/sched.h>	/* set_cpus_allowed() */
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+
+#include <asm/clock.h>
+
+#include <loongson.h>
+
+static uint nowait;
+
+static struct clk *cpuclk;
+
+static void (*saved_cpu_wait) (void);
+
+static int loongson2_cpu_freq_notifier(struct notifier_block *nb,
+					unsigned long val, void *data);
+
+static struct notifier_block loongson2_cpufreq_notifier_block = {
+	.notifier_call = loongson2_cpu_freq_notifier
+};
+
+static int loongson2_cpu_freq_notifier(struct notifier_block *nb,
+					unsigned long val, void *data)
+{
+	if (val == CPUFREQ_POSTCHANGE)
+		current_cpu_data.udelay_val = loops_per_jiffy;
+
+	return 0;
+}
+
+static unsigned int loongson2_cpufreq_get(unsigned int cpu)
+{
+	return clk_get_rate(cpuclk);
+}
+
+/*
+ * Here we notify other drivers of the proposed change and the final change.
+ */
+static int loongson2_cpufreq_target(struct cpufreq_policy *policy,
+				     unsigned int target_freq,
+				     unsigned int relation)
+{
+	unsigned int cpu = policy->cpu;
+	unsigned int newstate = 0;
+	cpumask_t cpus_allowed;
+	struct cpufreq_freqs freqs;
+	unsigned int freq;
+
+	if (!cpu_online(cpu))
+		return -ENODEV;
+
+	cpus_allowed = current->cpus_allowed;
+	set_cpus_allowed(current, cpumask_of_cpu(cpu));
+
+	if (cpufreq_frequency_table_target
+	    (policy, &loongson2_clockmod_table[0], target_freq, relation,
+	     &newstate))
+		return -EINVAL;
+
+	freq =
+	    ((cpu_clock_freq / 1000) *
+	     loongson2_clockmod_table[newstate].index) / 8;
+	if (freq < policy->min || freq > policy->max)
+		return -EINVAL;
+
+	pr_debug("cpufreq: requested frequency %u Hz\n", target_freq * 1000);
+
+	freqs.cpu = cpu;
+	freqs.old = loongson2_cpufreq_get(cpu);
+	freqs.new = freq;
+	freqs.flags = 0;
+
+	if (freqs.new == freqs.old)
+		return 0;
+
+	/* notifiers */
+	cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
+
+	set_cpus_allowed(current, cpus_allowed);
+
+	/* setting the cpu frequency */
+	clk_set_rate(cpuclk, freq);
+
+	/* notifiers */
+	cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
+
+	pr_debug("cpufreq: set frequency %u kHz\n", freq);
+
+	return 0;
+}
+
+static int loongson2_cpufreq_cpu_init(struct cpufreq_policy *policy)
+{
+	int i;
+
+	if (!cpu_online(policy->cpu))
+		return -ENODEV;
+
+	cpuclk = clk_get(NULL, "cpu_clk");
+	if (IS_ERR(cpuclk)) {
+		printk(KERN_ERR "cpufreq: couldn't get CPU clk\n");
+		return PTR_ERR(cpuclk);
+	}
+
+	cpuclk->rate = cpu_clock_freq / 1000;
+	if (!cpuclk->rate)
+		return -EINVAL;
+
+	/* clock table init */
+	for (i = 2;
+	     (loongson2_clockmod_table[i].frequency != CPUFREQ_TABLE_END);
+	     i++)
+		loongson2_clockmod_table[i].frequency = (cpuclk->rate * i) / 8;
+
+	policy->cur = loongson2_cpufreq_get(policy->cpu);
+
+	cpufreq_frequency_table_get_attr(&loongson2_clockmod_table[0],
+					 policy->cpu);
+
+	return cpufreq_frequency_table_cpuinfo(policy,
+					    &loongson2_clockmod_table[0]);
+}
+
+static int loongson2_cpufreq_verify(struct cpufreq_policy *policy)
+{
+	return cpufreq_frequency_table_verify(policy,
+					      &loongson2_clockmod_table[0]);
+}
+
+static int loongson2_cpufreq_exit(struct cpufreq_policy *policy)
+{
+	clk_put(cpuclk);
+	return 0;
+}
+
+static struct freq_attr *loongson2_table_attr[] = {
+	&cpufreq_freq_attr_scaling_available_freqs,
+	NULL,
+};
+
+static struct cpufreq_driver loongson2_cpufreq_driver = {
+	.owner = THIS_MODULE,
+	.name = "loongson2",
+	.init = loongson2_cpufreq_cpu_init,
+	.verify = loongson2_cpufreq_verify,
+	.target = loongson2_cpufreq_target,
+	.get = loongson2_cpufreq_get,
+	.exit = loongson2_cpufreq_exit,
+	.attr = loongson2_table_attr,
+};
+
+static struct platform_device_id platform_device_ids[] = {
+	{
+		.name = "loongson2_cpufreq",
+	},
+	{}
+};
+
+MODULE_DEVICE_TABLE(platform, platform_device_ids);
+
+static struct platform_driver platform_driver = {
+	.driver = {
+		.name = "loongson2_cpufreq",
+		.owner = THIS_MODULE,
+	},
+	.id_table = platform_device_ids,
+};
+
+static int __init cpufreq_init(void)
+{
+	int ret;
+
+	/* Register platform stuff */
+	ret = platform_driver_register(&platform_driver);
+	if (ret)
+		return ret;
+
+	pr_info("cpufreq: Loongson-2F CPU frequency driver.\n");
+
+	cpufreq_register_notifier(&loongson2_cpufreq_notifier_block,
+				  CPUFREQ_TRANSITION_NOTIFIER);
+
+	ret = cpufreq_register_driver(&loongson2_cpufreq_driver);
+
+	if (!ret && !nowait) {
+		saved_cpu_wait = cpu_wait;
+		cpu_wait = loongson2_cpu_wait;
+	}
+
+	return ret;
+}
+
+static void __exit cpufreq_exit(void)
+{
+	if (!nowait && saved_cpu_wait)
+		cpu_wait = saved_cpu_wait;
+	cpufreq_unregister_driver(&loongson2_cpufreq_driver);
+	cpufreq_unregister_notifier(&loongson2_cpufreq_notifier_block,
+				    CPUFREQ_TRANSITION_NOTIFIER);
+
+	platform_driver_unregister(&platform_driver);
+}
+
+module_init(cpufreq_init);
+module_exit(cpufreq_exit);
+
+module_param(nowait, uint, 0644);
+MODULE_PARM_DESC(nowait, "Disable Loongson-2F specific wait");
+
+MODULE_AUTHOR("Yanhua <yanh@lemote.com>");
+MODULE_DESCRIPTION("cpufreq driver for Loongson2F");
+MODULE_LICENSE("GPL");
diff --git a/arch/mips/loongson/Kconfig b/arch/mips/loongson/Kconfig
index 8b5cc138611a..7a86987b478f 100644
--- a/arch/mips/loongson/Kconfig
+++ b/arch/mips/loongson/Kconfig
@@ -34,10 +34,10 @@ config LEMOTE_MACH2F
 	select ARCH_SPARSEMEM_ENABLE
 	select BOARD_SCACHE
 	select BOOT_ELF32
-	select CEVT_R4K
+	select CEVT_R4K if ! MIPS_EXTERNAL_TIMER
 	select CPU_HAS_WB
 	select CS5536
-	select CSRC_R4K
+	select CSRC_R4K if ! MIPS_EXTERNAL_TIMER
 	select DMA_NONCOHERENT
 	select GENERIC_HARDIRQS_NO__DO_IRQ
 	select GENERIC_ISA_DMA_SUPPORT_BROKEN
@@ -65,6 +65,7 @@ config CS5536
 config CS5536_MFGPT
 	bool "CS5536 MFGPT Timer"
 	depends on CS5536
+	select MIPS_EXTERNAL_TIMER
 	help
 	  This option enables the mfgpt0 timer of AMD CS5536.
 
diff --git a/arch/mips/loongson/common/Makefile b/arch/mips/loongson/common/Makefile
index a21724d50e2c..8d71892413df 100644
--- a/arch/mips/loongson/common/Makefile
+++ b/arch/mips/loongson/common/Makefile
@@ -3,7 +3,7 @@
 #
 
 obj-y += setup.o init.o cmdline.o env.o time.o reset.o irq.o \
-    pci.o bonito-irq.o mem.o machtype.o uart_base.o
+    pci.o bonito-irq.o mem.o machtype.o platform.o uart_base.o
 
 #
 # Early printk support
diff --git a/arch/mips/loongson/common/env.c b/arch/mips/loongson/common/env.c
index b9ef50385541..196d947d929a 100644
--- a/arch/mips/loongson/common/env.c
+++ b/arch/mips/loongson/common/env.c
@@ -17,11 +17,14 @@
  * Free Software Foundation;  either version 2 of the  License, or (at your
  * option) any later version.
  */
+#include <linux/module.h>
+
 #include <asm/bootinfo.h>
 
 #include <loongson.h>
 
 unsigned long bus_clock, cpu_clock_freq;
+EXPORT_SYMBOL(cpu_clock_freq);
 unsigned long memsize, highmemsize;
 
 /* pmon passes arguments in 32bit pointers */
diff --git a/arch/mips/loongson/common/platform.c b/arch/mips/loongson/common/platform.c
new file mode 100644
index 000000000000..be81777eb94d
--- /dev/null
+++ b/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);