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path: root/drivers/cpufreq/bcm2835-cpufreq.c
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/*****************************************************************************
* Copyright 2011 Broadcom Corporation.  All rights reserved.
*
* Unless you and Broadcom execute a separate written software license
* agreement governing use of this software, this software is licensed to you
* under the terms of the GNU General Public License version 2, available at
* http://www.broadcom.com/licenses/GPLv2.php (the "GPL").
*
* Notwithstanding the above, under no circumstances may you combine this
* software in any way with any other Broadcom software provided under a
* license other than the GPL, without Broadcom's express prior written
* consent.
*****************************************************************************/

/*****************************************************************************
* FILENAME: bcm2835-cpufreq.h
* DESCRIPTION: This driver dynamically manages the CPU Frequency of the ARM
* processor. Messages are sent to Videocore either setting or requesting the
* frequency of the ARM in order to match an appropiate frequency to the current
* usage of the processor. The policy which selects the frequency to use is
* defined in the kernel .config file, but can be changed during runtime.
*****************************************************************************/

/* ---------- INCLUDES ---------- */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/cpufreq.h>
#include <mach/vcio.h>

/* ---------- DEFINES ---------- */
/*#define CPUFREQ_DEBUG_ENABLE*/		/* enable debugging */
#define MODULE_NAME "bcm2835-cpufreq"

#define VCMSG_ID_ARM_CLOCK 0x000000003		/* Clock/Voltage ID's */

/* debug printk macros */
#ifdef CPUFREQ_DEBUG_ENABLE
#define print_debug(fmt,...) pr_debug("%s:%s:%d: "fmt, MODULE_NAME, __func__, __LINE__, ##__VA_ARGS__)
#else
#define print_debug(fmt,...)
#endif
#define print_err(fmt,...) pr_err("%s:%s:%d: "fmt, MODULE_NAME, __func__,__LINE__, ##__VA_ARGS__)
#define print_info(fmt,...) pr_info("%s: "fmt, MODULE_NAME, ##__VA_ARGS__)

/* tag part of the message */
struct vc_msg_tag {
	uint32_t tag_id;		/* the message id */
	uint32_t buffer_size;		/* size of the buffer (which in this case is always 8 bytes) */
	uint32_t data_size;		/* amount of data being sent or received */
	uint32_t dev_id;		/* the ID of the clock/voltage to get or set */
	uint32_t val;			/* the value (e.g. rate (in Hz)) to set */
};

/* message structure to be sent to videocore */
struct vc_msg {
	uint32_t msg_size;		/* simply, sizeof(struct vc_msg) */
	uint32_t request_code;		/* holds various information like the success and number of bytes returned (refer to mailboxes wiki) */
	struct vc_msg_tag tag;		/* the tag structure above to make */
	uint32_t end_tag;		/* an end identifier, should be set to NULL */
};

/* ---------- GLOBALS ---------- */
static struct cpufreq_driver bcm2835_cpufreq_driver;	/* the cpufreq driver global */

static struct cpufreq_frequency_table bcm2835_freq_table[] = {
	{0, 0, 0},
	{0, 0, 0},
	{0, 0, CPUFREQ_TABLE_END},
};

/*
 ===============================================
  clk_rate either gets or sets the clock rates.
 ===============================================
*/
static uint32_t bcm2835_cpufreq_set_clock(int cur_rate, int arm_rate)
{
	int s, actual_rate=0;
	struct vc_msg msg;

	/* wipe all previous message data */
	memset(&msg, 0, sizeof msg);

	msg.msg_size = sizeof msg;

	msg.tag.tag_id = VCMSG_SET_CLOCK_RATE;
	msg.tag.buffer_size = 8;
	msg.tag.data_size = 8;   /* we're sending the clock ID and the new rates which is a total of 2 words */
	msg.tag.dev_id = VCMSG_ID_ARM_CLOCK;
	msg.tag.val = arm_rate * 1000;

	/* send the message */
	s = bcm_mailbox_property(&msg, sizeof msg);

	/* check if it was all ok and return the rate in KHz */
	if (s == 0 && (msg.request_code & 0x80000000))
		actual_rate = msg.tag.val/1000;

	print_debug("Setting new frequency = %d -> %d (actual %d)\n", cur_rate, arm_rate, actual_rate);
	return actual_rate;
}

static uint32_t bcm2835_cpufreq_get_clock(int tag)
{
	int s;
	int arm_rate = 0;
	struct vc_msg msg;

	/* wipe all previous message data */
	memset(&msg, 0, sizeof msg);

	msg.msg_size = sizeof msg;
	msg.tag.tag_id = tag;
	msg.tag.buffer_size = 8;
	msg.tag.data_size = 4; /* we're just sending the clock ID which is one word long */
	msg.tag.dev_id = VCMSG_ID_ARM_CLOCK;

	/* send the message */
	s = bcm_mailbox_property(&msg, sizeof msg);

	/* check if it was all ok and return the rate in KHz */
	if (s == 0 && (msg.request_code & 0x80000000))
		arm_rate = msg.tag.val/1000;

	print_debug("%s frequency = %d\n",
		tag == VCMSG_GET_CLOCK_RATE ? "Current":
		tag == VCMSG_GET_MIN_CLOCK ? "Min":
		tag == VCMSG_GET_MAX_CLOCK ? "Max":
		"Unexpected", arm_rate);

	return arm_rate;
}

/*
 ====================================================
  Module Initialisation registers the cpufreq driver
 ====================================================
*/
static int __init bcm2835_cpufreq_module_init(void)
{
	print_debug("IN\n");
	return cpufreq_register_driver(&bcm2835_cpufreq_driver);
}

/*
 =============
  Module exit
 =============
*/
static void __exit bcm2835_cpufreq_module_exit(void)
{
	print_debug("IN\n");
	cpufreq_unregister_driver(&bcm2835_cpufreq_driver);
	return;
}

/*
 ==============================================================
  Initialisation function sets up the CPU policy for first use
 ==============================================================
*/
static int bcm2835_cpufreq_driver_init(struct cpufreq_policy *policy)
{
	/* measured value of how long it takes to change frequency */
	const unsigned int transition_latency = 355000; /* ns */

	/* now find out what the maximum and minimum frequencies are */
	bcm2835_freq_table[0].frequency = bcm2835_cpufreq_get_clock(VCMSG_GET_MIN_CLOCK);
	bcm2835_freq_table[1].frequency = bcm2835_cpufreq_get_clock(VCMSG_GET_MAX_CLOCK);

	print_info("min=%d max=%d\n", bcm2835_freq_table[0].frequency, bcm2835_freq_table[1].frequency);
	return cpufreq_generic_init(policy, bcm2835_freq_table, transition_latency);
}

/*
 =====================================================================
  Target index function chooses the requested frequency from the table
 =====================================================================
*/

static int bcm2835_cpufreq_driver_target_index(struct cpufreq_policy *policy, unsigned int state)
{
	unsigned int target_freq = bcm2835_freq_table[state].frequency;
	unsigned int cur = bcm2835_cpufreq_set_clock(policy->cur, target_freq);

	if (!cur)
	{
		print_err("Error occurred setting a new frequency (%d)\n", target_freq);
		return -EINVAL;
	}
	print_debug("%s: %i: freq %d->%d\n", policy->governor->name, state, policy->cur, cur);
	return 0;
}

/*
 ======================================================
  Get function returns the current frequency from table
 ======================================================
*/

static unsigned int bcm2835_cpufreq_driver_get(unsigned int cpu)
{
	unsigned int actual_rate = bcm2835_cpufreq_get_clock(VCMSG_GET_CLOCK_RATE);
	print_debug("%d: freq=%d\n", cpu, actual_rate);
	return actual_rate <= bcm2835_freq_table[0].frequency ? bcm2835_freq_table[0].frequency : bcm2835_freq_table[1].frequency;
}

/* the CPUFreq driver */
static struct cpufreq_driver bcm2835_cpufreq_driver = {
	.name         = "BCM2835 CPUFreq",
	.init         = bcm2835_cpufreq_driver_init,
	.verify       = cpufreq_generic_frequency_table_verify,
	.target_index = bcm2835_cpufreq_driver_target_index,
	.get          = bcm2835_cpufreq_driver_get,
	.attr         = cpufreq_generic_attr,
};

MODULE_AUTHOR("Dorian Peake and Dom Cobley");
MODULE_DESCRIPTION("CPU frequency driver for BCM2835 chip");
MODULE_LICENSE("GPL");

module_init(bcm2835_cpufreq_module_init);
module_exit(bcm2835_cpufreq_module_exit);