drivers/cpufreq/cpufreq-nforce2.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * (C) 2004-2006  Sebastian Witt <se.witt@gmx.net>
  *
  *  Based upon reverse engineered information
  *
  *  BIG FAT DISCLAIMER: Work in progress code. Possibly *dangerous*
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/init.h>
 #include <linux/cpufreq.h>
 #include <linux/pci.h>
 #include <linux/delay.h>

 #define NFORCE2_XTAL 25
 #define NFORCE2_BOOTFSB 0x48
 #define NFORCE2_PLLENABLE 0xa8
 #define NFORCE2_PLLREG 0xa4
 #define NFORCE2_PLLADR 0xa0
 #define NFORCE2_PLL(mul, div) (0x100000 | (mul << 8) | div)

 #define NFORCE2_MIN_FSB 50
 #define NFORCE2_SAFE_DISTANCE 50

 /* Delay in ms between FSB changes */
 /* #define NFORCE2_DELAY 10 */

 /*
  * nforce2_chipset:
  * FSB is changed using the chipset
  */
 static struct pci_dev *nforce2_dev;

 /* fid:
  * multiplier * 10
  */
 static int fid;

 /* min_fsb, max_fsb:
  * minimum and maximum FSB (= FSB at boot time)
  */
 static int min_fsb;
 static int max_fsb;

 MODULE_AUTHOR("Sebastian Witt <se.witt@gmx.net>");
 MODULE_DESCRIPTION("nForce2 FSB changing cpufreq driver");
 MODULE_LICENSE("GPL");

 module_param(fid, int, 0444);
 module_param(min_fsb, int, 0444);

 MODULE_PARM_DESC(fid, "CPU multiplier to use (11.5 = 115)");
 MODULE_PARM_DESC(min_fsb,
 		"Minimum FSB to use, if not defined: current FSB - 50");

 /**
  * nforce2_calc_fsb - calculate FSB
  * @pll: PLL value
  *
  *   Calculates FSB from PLL value
  */
 static int nforce2_calc_fsb(int pll)
 {
 	unsigned char mul, div;

 	mul = (pll >> 8) & 0xff;
 	div = pll & 0xff;

 	if (div > 0)
 		return NFORCE2_XTAL * mul / div;

 	return 0;
 }

 /**
  * nforce2_calc_pll - calculate PLL value
  * @fsb: FSB
  *
  *   Calculate PLL value for given FSB
  */
 static int nforce2_calc_pll(unsigned int fsb)
 {
 	unsigned char xmul, xdiv;
 	unsigned char mul = 0, div = 0;
 	int tried = 0;

 	/* Try to calculate multiplier and divider up to 4 times */
 	while (((mul == 0) || (div == 0)) && (tried <= 3)) {
 		for (xdiv = 2; xdiv <= 0x80; xdiv++)
 			for (xmul = 1; xmul <= 0xfe; xmul++)
 				if (nforce2_calc_fsb(NFORCE2_PLL(xmul, xdiv)) ==
 				    fsb + tried) {
 					mul = xmul;
 					div = xdiv;
 				}
 		tried++;
 	}

 	if ((mul == 0) || (div == 0))
 		return -1;

 	return NFORCE2_PLL(mul, div);
 }

 /**
  * nforce2_write_pll - write PLL value to chipset
  * @pll: PLL value
  *
  *   Writes new FSB PLL value to chipset
  */
 static void nforce2_write_pll(int pll)
 {
 	int temp;

 	/* Set the pll addr. to 0x00 */
 	pci_write_config_dword(nforce2_dev, NFORCE2_PLLADR, 0);

 	/* Now write the value in all 64 registers */
 	for (temp = 0; temp <= 0x3f; temp++)
 		pci_write_config_dword(nforce2_dev, NFORCE2_PLLREG, pll);
 }

 /**
  * nforce2_fsb_read - Read FSB
  *
  *   Read FSB from chipset
  *   If bootfsb != 0, return FSB at boot-time
  */
 static unsigned int nforce2_fsb_read(int bootfsb)
 {
 	struct pci_dev *nforce2_sub5;
 	u32 fsb, temp = 0;

 	/* Get chipset boot FSB from subdevice 5 (FSB at boot-time) */
 	nforce2_sub5 = pci_get_subsys(PCI_VENDOR_ID_NVIDIA, 0x01EF,
 				PCI_ANY_ID, PCI_ANY_ID, NULL);
 	if (!nforce2_sub5)
 		return 0;

 	pci_read_config_dword(nforce2_sub5, NFORCE2_BOOTFSB, &fsb);
 	fsb /= 1000000;

 	/* Check if PLL register is already set */
 	pci_read_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8 *)&temp);

 	if (bootfsb || !temp)
 		return fsb;

 	/* Use PLL register FSB value */
 	pci_read_config_dword(nforce2_dev, NFORCE2_PLLREG, &temp);
 	fsb = nforce2_calc_fsb(temp);

 	return fsb;
 }

 /**
  * nforce2_set_fsb - set new FSB
  * @fsb: New FSB
  *
  *   Sets new FSB
  */
 static int nforce2_set_fsb(unsigned int fsb)
 {
 	u32 temp = 0;
 	unsigned int tfsb;
 	int diff;
 	int pll = 0;

 	if ((fsb > max_fsb) || (fsb < NFORCE2_MIN_FSB)) {
 		pr_err("FSB %d is out of range!\n", fsb);
 		return -EINVAL;
 	}

 	tfsb = nforce2_fsb_read(0);
 	if (!tfsb) {
 		pr_err("Error while reading the FSB\n");
 		return -EINVAL;
 	}

 	/* First write? Then set actual value */
 	pci_read_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8 *)&temp);
 	if (!temp) {
 		pll = nforce2_calc_pll(tfsb);

 		if (pll < 0)
 			return -EINVAL;

 		nforce2_write_pll(pll);
 	}

 	/* Enable write access */
 	temp = 0x01;
 	pci_write_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8)temp);

 	diff = tfsb - fsb;

 	if (!diff)
 		return 0;

 	while ((tfsb != fsb) && (tfsb <= max_fsb) && (tfsb >= min_fsb)) {
 		if (diff < 0)
 			tfsb++;
 		else
 			tfsb--;

 		/* Calculate the PLL reg. value */
 		pll = nforce2_calc_pll(tfsb);
 		if (pll == -1)
 			return -EINVAL;

 		nforce2_write_pll(pll);
 #ifdef NFORCE2_DELAY
 		mdelay(NFORCE2_DELAY);
 #endif
 	}

 	temp = 0x40;
 	pci_write_config_byte(nforce2_dev, NFORCE2_PLLADR, (u8)temp);

 	return 0;
 }

 /**
  * nforce2_get - get the CPU frequency
  * @cpu: CPU number
  *
  * Returns the CPU frequency
  */
 static unsigned int nforce2_get(unsigned int cpu)
 {
 	if (cpu)
 		return 0;
 	return nforce2_fsb_read(0) * fid * 100;
 }

 /**
  * nforce2_target - set a new CPUFreq policy
  * @policy: new policy
  * @target_freq: the target frequency
  * @relation: how that frequency relates to achieved frequency
  *  (CPUFREQ_RELATION_L or CPUFREQ_RELATION_H)
  *
  * Sets a new CPUFreq policy.
  */
 static int nforce2_target(struct cpufreq_policy *policy,
 			  unsigned int target_freq, unsigned int relation)
 {
 /*        unsigned long         flags; */
 	struct cpufreq_freqs freqs;
 	unsigned int target_fsb;

 	if ((target_freq > policy->max) || (target_freq < policy->min))
 		return -EINVAL;

 	target_fsb = target_freq / (fid * 100);

 	freqs.old = nforce2_get(policy->cpu);
 	freqs.new = target_fsb * fid * 100;

 	if (freqs.old == freqs.new)
 		return 0;

 	pr_debug("Old CPU frequency %d kHz, new %d kHz\n",
 	       freqs.old, freqs.new);

 	cpufreq_freq_transition_begin(policy, &freqs);

 	/* Disable IRQs */
 	/* local_irq_save(flags); */

 	if (nforce2_set_fsb(target_fsb) < 0)
 		pr_err("Changing FSB to %d failed\n", target_fsb);
 	else
 		pr_debug("Changed FSB successfully to %d\n",
 			target_fsb);

 	/* Enable IRQs */
 	/* local_irq_restore(flags); */

 	cpufreq_freq_transition_end(policy, &freqs, 0);

 	return 0;
 }

 /**
  * nforce2_verify - verifies a new CPUFreq policy
  * @policy: new policy
  */
 static int nforce2_verify(struct cpufreq_policy_data *policy)
 {
 	unsigned int fsb_pol_max;

 	fsb_pol_max = policy->max / (fid * 100);

 	if (policy->min < (fsb_pol_max * fid * 100))
 		policy->max = (fsb_pol_max + 1) * fid * 100;

 	cpufreq_verify_within_cpu_limits(policy);
 	return 0;
 }

 static int nforce2_cpu_init(struct cpufreq_policy *policy)
 {
 	unsigned int fsb;
 	unsigned int rfid;

 	/* capability check */
 	if (policy->cpu != 0)
 		return -ENODEV;

 	/* Get current FSB */
 	fsb = nforce2_fsb_read(0);

 	if (!fsb)
 		return -EIO;

 	/* FIX: Get FID from CPU */
 	if (!fid) {
 		if (!cpu_khz) {
 			pr_warn("cpu_khz not set, can't calculate multiplier!\n");
 			return -ENODEV;
 		}

 		fid = cpu_khz / (fsb * 100);
 		rfid = fid % 5;

 		if (rfid) {
 			if (rfid > 2)
 				fid += 5 - rfid;
 			else
 				fid -= rfid;
 		}
 	}

 	pr_info("FSB currently at %i MHz, FID %d.%d\n",
 		fsb, fid / 10, fid % 10);

 	/* Set maximum FSB to FSB at boot time */
 	max_fsb = nforce2_fsb_read(1);

 	if (!max_fsb)
 		return -EIO;

 	if (!min_fsb)
 		min_fsb = max_fsb - NFORCE2_SAFE_DISTANCE;

 	if (min_fsb < NFORCE2_MIN_FSB)
 		min_fsb = NFORCE2_MIN_FSB;

 	/* cpuinfo and default policy values */
 	policy->min = policy->cpuinfo.min_freq = min_fsb * fid * 100;
 	policy->max = policy->cpuinfo.max_freq = max_fsb * fid * 100;

 	return 0;
 }

 static struct cpufreq_driver nforce2_driver = {
 	.name = "nforce2",
 	.flags = CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
 	.verify = nforce2_verify,
 	.target = nforce2_target,
 	.get = nforce2_get,
 	.init = nforce2_cpu_init,
 };

 #ifdef MODULE
 static const struct pci_device_id nforce2_ids[] = {
 	{ PCI_VENDOR_ID_NVIDIA, PCI_DEVICE_ID_NVIDIA_NFORCE2 },
 	{}
 };
 MODULE_DEVICE_TABLE(pci, nforce2_ids);
 #endif

 /**
  * nforce2_detect_chipset - detect the Southbridge which contains FSB PLL logic
  *
  * Detects nForce2 A2 and C1 stepping
  *
  */
 static int nforce2_detect_chipset(void)
 {
 	nforce2_dev = pci_get_subsys(PCI_VENDOR_ID_NVIDIA,
 					PCI_DEVICE_ID_NVIDIA_NFORCE2,
 					PCI_ANY_ID, PCI_ANY_ID, NULL);

 	if (nforce2_dev == NULL)
 		return -ENODEV;

 	pr_info("Detected nForce2 chipset revision %X\n",
 		nforce2_dev->revision);
 	pr_info("FSB changing is maybe unstable and can lead to crashes and data loss\n");

 	return 0;
 }

 /**
  * nforce2_init - initializes the nForce2 CPUFreq driver
  *
  * Initializes the nForce2 FSB support. Returns -ENODEV on unsupported
  * devices, -EINVAL on problems during initialization, and zero on
  * success.
  */
 static int __init nforce2_init(void)
 {
 	/* TODO: do we need to detect the processor? */

 	/* detect chipset */
 	if (nforce2_detect_chipset()) {
 		pr_info("No nForce2 chipset\n");
 		return -ENODEV;
 	}

 	return cpufreq_register_driver(&nforce2_driver);
 }

 /**
  * nforce2_exit - unregisters cpufreq module
  *
  *   Unregisters nForce2 FSB change support.
  */
 static void __exit nforce2_exit(void)
 {
 	cpufreq_unregister_driver(&nforce2_driver);
 }

 module_init(nforce2_init);
 module_exit(nforce2_exit);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* (C) 2004-2006 Sebastian Witt <se.witt@gmx.net>
	*
	* Based upon reverse engineered information
	*
	* BIG FAT DISCLAIMER: Work in progress code. Possibly dangerous
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/moduleparam.h>
	#include <linux/init.h>
	#include <linux/cpufreq.h>
	#include <linux/pci.h>
	#include <linux/delay.h>

	#define NFORCE2_XTAL 25
	#define NFORCE2_BOOTFSB 0x48
	#define NFORCE2_PLLENABLE 0xa8
	#define NFORCE2_PLLREG 0xa4
	#define NFORCE2_PLLADR 0xa0
	#define NFORCE2_PLL(mul, div) (0x100000 \| (mul << 8) \| div)

	#define NFORCE2_MIN_FSB 50
	#define NFORCE2_SAFE_DISTANCE 50

	/* Delay in ms between FSB changes */
	/* #define NFORCE2_DELAY 10 */

	/*
	* nforce2_chipset:
	* FSB is changed using the chipset
	*/
	static struct pci_dev *nforce2_dev;

	/* fid:
	* multiplier * 10
	*/
	static int fid;

	/* min_fsb, max_fsb:
	* minimum and maximum FSB (= FSB at boot time)
	*/
	static int min_fsb;
	static int max_fsb;

	MODULE_AUTHOR("Sebastian Witt <se.witt@gmx.net>");
	MODULE_DESCRIPTION("nForce2 FSB changing cpufreq driver");
	MODULE_LICENSE("GPL");

	module_param(fid, int, 0444);
	module_param(min_fsb, int, 0444);

	MODULE_PARM_DESC(fid, "CPU multiplier to use (11.5 = 115)");
	MODULE_PARM_DESC(min_fsb,
	"Minimum FSB to use, if not defined: current FSB - 50");

	/**
	* nforce2_calc_fsb - calculate FSB
	* @pll: PLL value
	*
	* Calculates FSB from PLL value
	*/
	static int nforce2_calc_fsb(int pll)
	{
	unsigned char mul, div;

	mul = (pll >> 8) & 0xff;
	div = pll & 0xff;

	if (div > 0)
	return NFORCE2_XTAL * mul / div;

	return 0;
	}

	/**
	* nforce2_calc_pll - calculate PLL value
	* @fsb: FSB
	*
	* Calculate PLL value for given FSB
	*/
	static int nforce2_calc_pll(unsigned int fsb)
	{
	unsigned char xmul, xdiv;
	unsigned char mul = 0, div = 0;
	int tried = 0;

	/* Try to calculate multiplier and divider up to 4 times */
	while (((mul == 0) \|\| (div == 0)) && (tried <= 3)) {
	for (xdiv = 2; xdiv <= 0x80; xdiv++)
	for (xmul = 1; xmul <= 0xfe; xmul++)
	if (nforce2_calc_fsb(NFORCE2_PLL(xmul, xdiv)) ==
	fsb + tried) {
	mul = xmul;
	div = xdiv;
	}
	tried++;
	}

	if ((mul == 0) \|\| (div == 0))
	return -1;

	return NFORCE2_PLL(mul, div);
	}

	/**
	* nforce2_write_pll - write PLL value to chipset
	* @pll: PLL value
	*
	* Writes new FSB PLL value to chipset
	*/
	static void nforce2_write_pll(int pll)
	{
	int temp;

	/* Set the pll addr. to 0x00 */
	pci_write_config_dword(nforce2_dev, NFORCE2_PLLADR, 0);

	/* Now write the value in all 64 registers */
	for (temp = 0; temp <= 0x3f; temp++)
	pci_write_config_dword(nforce2_dev, NFORCE2_PLLREG, pll);
	}

	/**
	* nforce2_fsb_read - Read FSB
	*
	* Read FSB from chipset
	* If bootfsb != 0, return FSB at boot-time
	*/
	static unsigned int nforce2_fsb_read(int bootfsb)
	{
	struct pci_dev *nforce2_sub5;
	u32 fsb, temp = 0;

	/* Get chipset boot FSB from subdevice 5 (FSB at boot-time) */
	nforce2_sub5 = pci_get_subsys(PCI_VENDOR_ID_NVIDIA, 0x01EF,
	PCI_ANY_ID, PCI_ANY_ID, NULL);
	if (!nforce2_sub5)
	return 0;

	pci_read_config_dword(nforce2_sub5, NFORCE2_BOOTFSB, &fsb);
	fsb /= 1000000;

	/* Check if PLL register is already set */
	pci_read_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8 *)&temp);

	if (bootfsb \|\| !temp)
	return fsb;

	/* Use PLL register FSB value */
	pci_read_config_dword(nforce2_dev, NFORCE2_PLLREG, &temp);
	fsb = nforce2_calc_fsb(temp);

	return fsb;
	}

	/**
	* nforce2_set_fsb - set new FSB
	* @fsb: New FSB
	*
	* Sets new FSB
	*/
	static int nforce2_set_fsb(unsigned int fsb)
	{
	u32 temp = 0;
	unsigned int tfsb;
	int diff;
	int pll = 0;

	if ((fsb > max_fsb) \|\| (fsb < NFORCE2_MIN_FSB)) {
	pr_err("FSB %d is out of range!\n", fsb);
	return -EINVAL;
	}

	tfsb = nforce2_fsb_read(0);
	if (!tfsb) {
	pr_err("Error while reading the FSB\n");
	return -EINVAL;
	}

	/* First write? Then set actual value */
	pci_read_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8 *)&temp);
	if (!temp) {
	pll = nforce2_calc_pll(tfsb);

	if (pll < 0)
	return -EINVAL;

	nforce2_write_pll(pll);
	}

	/* Enable write access */
	temp = 0x01;
	pci_write_config_byte(nforce2_dev, NFORCE2_PLLENABLE, (u8)temp);

	diff = tfsb - fsb;

	if (!diff)
	return 0;

	while ((tfsb != fsb) && (tfsb <= max_fsb) && (tfsb >= min_fsb)) {
	if (diff < 0)
	tfsb++;
	else
	tfsb--;

	/* Calculate the PLL reg. value */
	pll = nforce2_calc_pll(tfsb);
	if (pll == -1)
	return -EINVAL;

	nforce2_write_pll(pll);
	#ifdef NFORCE2_DELAY
	mdelay(NFORCE2_DELAY);
	#endif
	}

	temp = 0x40;
	pci_write_config_byte(nforce2_dev, NFORCE2_PLLADR, (u8)temp);

	return 0;
	}

	/**
	* nforce2_get - get the CPU frequency
	* @cpu: CPU number
	*
	* Returns the CPU frequency
	*/
	static unsigned int nforce2_get(unsigned int cpu)
	{
	if (cpu)
	return 0;
	return nforce2_fsb_read(0) * fid * 100;
	}

	/**
	* nforce2_target - set a new CPUFreq policy
	* @policy: new policy
	* @target_freq: the target frequency
	* @relation: how that frequency relates to achieved frequency
	* (CPUFREQ_RELATION_L or CPUFREQ_RELATION_H)
	*
	* Sets a new CPUFreq policy.
	*/
	static int nforce2_target(struct cpufreq_policy *policy,
	unsigned int target_freq, unsigned int relation)
	{
	/* unsigned long flags; */
	struct cpufreq_freqs freqs;
	unsigned int target_fsb;

	if ((target_freq > policy->max) \|\| (target_freq < policy->min))
	return -EINVAL;

	target_fsb = target_freq / (fid * 100);

	freqs.old = nforce2_get(policy->cpu);
	freqs.new = target_fsb * fid * 100;

	if (freqs.old == freqs.new)
	return 0;

	pr_debug("Old CPU frequency %d kHz, new %d kHz\n",
	freqs.old, freqs.new);

	cpufreq_freq_transition_begin(policy, &freqs);

	/* Disable IRQs */
	/* local_irq_save(flags); */

	if (nforce2_set_fsb(target_fsb) < 0)
	pr_err("Changing FSB to %d failed\n", target_fsb);
	else
	pr_debug("Changed FSB successfully to %d\n",
	target_fsb);

	/* Enable IRQs */
	/* local_irq_restore(flags); */

	cpufreq_freq_transition_end(policy, &freqs, 0);

	return 0;
	}

	/**
	* nforce2_verify - verifies a new CPUFreq policy
	* @policy: new policy
	*/
	static int nforce2_verify(struct cpufreq_policy_data *policy)
	{
	unsigned int fsb_pol_max;

	fsb_pol_max = policy->max / (fid * 100);

	if (policy->min < (fsb_pol_max * fid * 100))
	policy->max = (fsb_pol_max + 1) * fid * 100;

	cpufreq_verify_within_cpu_limits(policy);
	return 0;
	}

	static int nforce2_cpu_init(struct cpufreq_policy *policy)
	{
	unsigned int fsb;
	unsigned int rfid;

	/* capability check */
	if (policy->cpu != 0)
	return -ENODEV;

	/* Get current FSB */
	fsb = nforce2_fsb_read(0);

	if (!fsb)
	return -EIO;

	/* FIX: Get FID from CPU */
	if (!fid) {
	if (!cpu_khz) {
	pr_warn("cpu_khz not set, can't calculate multiplier!\n");
	return -ENODEV;
	}

	fid = cpu_khz / (fsb * 100);
	rfid = fid % 5;

	if (rfid) {
	if (rfid > 2)
	fid += 5 - rfid;
	else
	fid -= rfid;
	}
	}

	pr_info("FSB currently at %i MHz, FID %d.%d\n",
	fsb, fid / 10, fid % 10);

	/* Set maximum FSB to FSB at boot time */
	max_fsb = nforce2_fsb_read(1);

	if (!max_fsb)
	return -EIO;

	if (!min_fsb)
	min_fsb = max_fsb - NFORCE2_SAFE_DISTANCE;

	if (min_fsb < NFORCE2_MIN_FSB)
	min_fsb = NFORCE2_MIN_FSB;

	/* cpuinfo and default policy values */
	policy->min = policy->cpuinfo.min_freq = min_fsb * fid * 100;
	policy->max = policy->cpuinfo.max_freq = max_fsb * fid * 100;

	return 0;
	}

	static struct cpufreq_driver nforce2_driver = {
	.name = "nforce2",
	.flags = CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
	.verify = nforce2_verify,
	.target = nforce2_target,
	.get = nforce2_get,
	.init = nforce2_cpu_init,
	};

	#ifdef MODULE
	static const struct pci_device_id nforce2_ids[] = {
	{ PCI_VENDOR_ID_NVIDIA, PCI_DEVICE_ID_NVIDIA_NFORCE2 },
	{}
	};
	MODULE_DEVICE_TABLE(pci, nforce2_ids);
	#endif

	/**
	* nforce2_detect_chipset - detect the Southbridge which contains FSB PLL logic
	*
	* Detects nForce2 A2 and C1 stepping
	*
	*/
	static int nforce2_detect_chipset(void)
	{
	nforce2_dev = pci_get_subsys(PCI_VENDOR_ID_NVIDIA,
	PCI_DEVICE_ID_NVIDIA_NFORCE2,
	PCI_ANY_ID, PCI_ANY_ID, NULL);

	if (nforce2_dev == NULL)
	return -ENODEV;

	pr_info("Detected nForce2 chipset revision %X\n",
	nforce2_dev->revision);
	pr_info("FSB changing is maybe unstable and can lead to crashes and data loss\n");

	return 0;
	}

	/**
	* nforce2_init - initializes the nForce2 CPUFreq driver
	*
	* Initializes the nForce2 FSB support. Returns -ENODEV on unsupported
	* devices, -EINVAL on problems during initialization, and zero on
	* success.
	*/
	static int __init nforce2_init(void)
	{
	/* TODO: do we need to detect the processor? */

	/* detect chipset */
	if (nforce2_detect_chipset()) {
	pr_info("No nForce2 chipset\n");
	return -ENODEV;
	}

	return cpufreq_register_driver(&nforce2_driver);
	}

	/**
	* nforce2_exit - unregisters cpufreq module
	*
	* Unregisters nForce2 FSB change support.
	*/
	static void __exit nforce2_exit(void)
	{
	cpufreq_unregister_driver(&nforce2_driver);
	}

	module_init(nforce2_init);
	module_exit(nforce2_exit);