[RFC] Temperature sensor driver (tango)

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

Hello,

I've written a temperature sensor driver for my SoC, with the
intent of using it for CPU throttling, using cpufreq levels.
(I think that's called passive cooling.)

For testing purposes, I've added two nodes to my DT:

	soc {
		cpu_temp: sensor@920100 {
			compatible = "sigma,smp8758-sensor";
			#thermal-sensor-cells = <0>;
			reg = <0x920100 12>;
		};
	};

	thermal-zones {
		cpu_thermal: cpu-thermal {
			thermal-sensors = <&cpu_temp>;
		};
	};

I'd like to submit the driver for inclusion upstream, so I'm
making this request for comments on the driver. (I suppose I
would also need to change Makefile/Kconfig?)


#include <linux/io.h>
#include <linux/module.h>
#include <linux/thermal.h>
#include <linux/platform_device.h>

#define TEMPSI_CMD	0
#define TEMPSI_RES	4
#define TEMPSI_CFG	8

#define CMD_OFF		0
#define CMD_ON		1
#define CMD_READ	2

#define sensor_idle(base)	(readl_relaxed(base + TEMPSI_CMD) & BIT(7))
#define TEMP_LESS_THAN_THRESH	0
#define INDEX_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,
};

static int tango_get_temp(void *arg, int *res)
{
	int i;
	void __iomem *base = arg;

	for (i = 0; i < 24; ++i)
	{
		int thresh_idx = INDEX_OFFSET + i;
		writel_relaxed(thresh_idx << 8 | CMD_READ, base + TEMPSI_CMD);

		while (!sensor_idle(base))
			cpu_relax();

		if (readl_relaxed(base + TEMPSI_RES) == TEMP_LESS_THAN_THRESH)
			break;
	}

	writel_relaxed(INDEX_OFFSET << 8 | CMD_READ, base + TEMPSI_CMD);
	*res = temperature[i] * 1000;
	return 0;
}

static const struct thermal_zone_of_device_ops ops = {
	.get_temp	= tango_get_temp,
};

struct tango_thermal_priv {
	struct thermal_zone_device *zone;
	void __iomem *base;
};

static int tango_thermal_probe(struct platform_device *pdev)
{
	struct resource *res;
	struct tango_thermal_priv *priv;
	struct device *dev = &pdev->dev;

	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	priv->base = devm_ioremap_resource(dev, res);
	if (IS_ERR(priv->base))
		return PTR_ERR(priv->base);

	writel_relaxed(CMD_ON, priv->base + TEMPSI_CMD);
	writel_relaxed(    50, priv->base + TEMPSI_CFG);

	priv->zone = thermal_zone_of_sensor_register(dev, 0, priv->base, &ops);
	if (IS_ERR(priv->zone))
		return PTR_ERR(priv->zone);

	platform_set_drvdata(pdev, priv);
	return 0;
}

static int tango_thermal_remove(struct platform_device *pdev)
{
	struct tango_thermal_priv *priv = platform_get_drvdata(pdev);

	thermal_zone_of_sensor_unregister(&pdev->dev, priv->zone);

	writel_relaxed(      0, priv->base + TEMPSI_CFG);
	writel_relaxed(CMD_OFF, priv->base + TEMPSI_CMD);

	return 0;
}

static const struct of_device_id tango_sensor_ids[] = {
	{
		.compatible = "sigma,smp8758-sensor",
	},
	{ /* sentinel */ }
};

static struct platform_driver tango_thermal_driver = {
	.probe	= tango_thermal_probe,
	.remove	= tango_thermal_remove,
	.driver	= {
		.name		= "tango-thermal",
		.of_match_table	= tango_sensor_ids,
	},
};

module_platform_driver(tango_thermal_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sigma Designs");
MODULE_DESCRIPTION("Tango temperature sensor");