Re: Using a temperature sensor with 1-bit output for CPU throttling

[Mason <slash.tmp@free.fr>]

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On 21/07/2015 11:10, Mason wrote:

> I don't think I want on/off behavior. I want CPU throttling when
> the temperature rises above a user-defined value.
> 
> I'm stuck with kernel 3.14, so I don't have all the governors to
> choose from. I picked "step-wise".

I think the attached driver does what I want. (If anyone wants to
comment on the code, I'd be delighted to hear their suggestions!
Especially if there's a better way to do something.)

When the CPU temperature exceeds a user-defined threshold (default
120 °C) the maximum frequency is disabled for all cores (they are
in the same clock domain), and the system will only run at F/2
(at most) until the temperature dips below the threshold.

Does the cpu_cooling driver written by Amit Daniel also support
disabling/off-lining entire cores in multi-core systems, not just
throttling the frequency of the cores?

Regards.


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#include <linux/module.h>
#include <linux/io.h>		// readl_relaxed, writel_relaxed
#include <linux/cpu_cooling.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sigma Designs");
MODULE_DESCRIPTION("Tango CPU throttling");

/*** CPU TEMPERATURE SENSOR ***/
#define SENSOR_ADDR 0x920100
static struct thermal_cooling_device *tcdev;
static struct thermal_zone_device *tzdev;
static void __iomem *sensor_base;
static unsigned int threshold;

#define TEMPSI_CMD	sensor_base + 0
#define TEMPSI_RES	sensor_base + 4
#define TEMPSI_CFG	sensor_base + 8
#define SENSOR_IDLE	(readl_relaxed(TEMPSI_CMD) & 0x80)
#define IDX_OFFSET	18

static const u8 temperature[] = {
	 37,  41,  46,  51,  55,  60,  64,  69,
	 74,  79,  83,  88,  93,  97, 101, 106,
	110, 115, 120, 124, 129, 133, 137, 142,
};

typedef struct thermal_zone_device TZD;

static int tango_get_temp(TZD *tz, unsigned long *res)
{
	int i;

	for (i = IDX_OFFSET; i < 40; ++i)
	{
		writel_relaxed(i << 8 | 2, TEMPSI_CMD);
		while (!SENSOR_IDLE);
		if (readl_relaxed(TEMPSI_RES) == 0) break;
	}

	*res = temperature[i - IDX_OFFSET] * 1000;
	return 0;
}

static int tango_bind(TZD *tz, struct thermal_cooling_device *cdev)
{
	/*
	 * Disable max frequency when CPU temperature exceeds trip point
	 * by setting upper and lower cooling states to 1
	 */
	return thermal_zone_bind_cooling_device(tz, 0, cdev, 1, 1);
}

static int tango_unbind(TZD *tz, struct thermal_cooling_device *cdev)
{
	return thermal_zone_unbind_cooling_device(tz, 0, cdev);
}

static int tango_get_trip_type(TZD *tz, int idx, enum thermal_trip_type *res)
{
	*res = THERMAL_TRIP_PASSIVE;
	return 0;
}

static int tango_get_trip_temp(TZD *tz, int idx, unsigned long *res)
{
	*res = threshold;
	return 0;
}

static int tango_set_trip_temp(TZD *tz, int idx, unsigned long res)
{
	threshold = res;
	return 0;
}

static struct thermal_zone_device_ops ops = {
	.bind		= tango_bind,
	.unbind		= tango_unbind,
	.get_temp	= tango_get_temp,
	.get_trip_type	= tango_get_trip_type,
	.get_trip_temp	= tango_get_trip_temp,
	.set_trip_temp	= tango_set_trip_temp,
};

static int ts_init(void)
{
	threshold = 120000; // millidegrees Celsius
	sensor_base = ioremap(SENSOR_ADDR, 16);
	writel_relaxed( 1, TEMPSI_CMD);
	writel_relaxed(50, TEMPSI_CFG);
	tcdev = cpufreq_cooling_register(cpu_present_mask);
	tzdev = thermal_zone_device_register("tango_thermal", 1, 1, NULL, &ops, NULL, 1000, 2000);
	return 0;
}

static void __exit ts_cleanup(void)
{
	thermal_zone_device_unregister(tzdev);
	cpufreq_cooling_unregister(tcdev);
	writel_relaxed(0, TEMPSI_CFG);
	writel_relaxed(0, TEMPSI_CMD);
}

module_init(ts_init);
module_exit(ts_cleanup);