drivers/hwmon/ptc_thermistor.c - manifest_repos/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * The driver is developed based on ntc_thermistor driver.
  *
  * Copyright 2020 Google LLC.
  */

 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/math64.h>
 #include <linux/platform_device.h>
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/of_device.h>

 #include <linux/platform_data/ptc_thermistor.h>

 #include <linux/iio/iio.h>
 #include <linux/iio/machine.h>
 #include <linux/iio/driver.h>
 #include <linux/iio/consumer.h>

 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
 #include <linux/thermal.h>

 struct ptc_compensation {
 	int	temp_c;
 	unsigned int	ohm;
 };

 /* Order matters, ptc_match references the entries by index */
 static const struct platform_device_id ptc_thermistor_id[] = {
 	{ "tmp6331decr,v,conf1", TYPE_TMP6331DECR_VBIAS_1_8_V_100000_OHM },
 	{ },
 };

 /*
  * temp_c in descending order for PTC thermistors
  */
 static const struct ptc_compensation comp_tmp6331decr_vbias_1_8v_100000_ohm[] = {
 	{ .temp_c	= 125, .ohm	= 175288 },
 	{ .temp_c	= 120, .ohm	= 170610 },
 	{ .temp_c	= 115, .ohm	= 166029 },
 	{ .temp_c	= 110, .ohm	= 161541 },
 	{ .temp_c	= 105, .ohm	= 157146 },
 	{ .temp_c	= 100, .ohm	= 152841 },
 	{ .temp_c	= 95, .ohm	= 148626 },
 	{ .temp_c	= 90, .ohm	= 144498 },
 	{ .temp_c	= 85, .ohm	= 140457 },
 	{ .temp_c	= 80, .ohm	= 136502 },
 	{ .temp_c	= 75, .ohm	= 132630 },
 	{ .temp_c	= 70, .ohm	= 128840 },
 	{ .temp_c	= 65, .ohm	= 125133 },
 	{ .temp_c	= 60, .ohm	= 121506 },
 	{ .temp_c	= 55, .ohm	= 117958 },
 	{ .temp_c	= 50, .ohm	= 114489 },
 	{ .temp_c	= 45, .ohm	= 111098 },
 	{ .temp_c	= 40, .ohm	= 107783 },
 	{ .temp_c	= 35, .ohm	= 104545 },
 	{ .temp_c	= 30, .ohm	= 101383 },
 	{ .temp_c	= 25, .ohm	= 98295 },
 	{ .temp_c	= 20, .ohm	= 95281 },
 	{ .temp_c	= 15, .ohm	= 92342 },
 	{ .temp_c	= 10, .ohm	= 89475 },
 	{ .temp_c	= 5, .ohm	= 86682 },
 	{ .temp_c	= 0, .ohm	= 83961 },
 	{ .temp_c	= -5, .ohm	= 81312 },
 	{ .temp_c	= -10, .ohm	= 78736 },
 	{ .temp_c	= -15, .ohm	= 76232 },
 	{ .temp_c	= -20, .ohm	= 73800 },
 	{ .temp_c	= -25, .ohm	= 71439 },
 	{ .temp_c	= -30, .ohm	= 69151 },
 	{ .temp_c	= -35, .ohm	= 66935 },
 	{ .temp_c	= -40, .ohm	= 64791 },
 };

 struct ptc_data {
 	struct ptc_thermistor_platform_data *pdata;
 	const struct ptc_compensation *comp;
 	int n_comp;
 	int offset_mc;
 };

 #if defined(CONFIG_OF) && IS_ENABLED(CONFIG_IIO)
 static int ptc_adc_iio_read(struct ptc_thermistor_platform_data *pdata)
 {
 	struct iio_channel *channel = pdata->chan;
 	int raw, uv, ret;

 	ret = iio_read_channel_raw(channel, &raw);
 	if (ret < 0) {
 		pr_err("read channel() error: %d\n", ret);
 		return ret;
 	}

 	ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
 	if (ret < 0) {
 		/* Assume 12 bit ADC with vref at pullup_uv */
 		uv = (pdata->pullup_uv * (s64)raw) >> 12;
 	}

 	return uv;
 }

 static const struct of_device_id ptc_match[] = {
 	{ .compatible = "ti,tmp6331decr,vbias-1.8v-100000ohm",
 		.data = &ptc_thermistor_id[0] },
 	{ },
 };
 MODULE_DEVICE_TABLE(of, ptc_match);

 static struct ptc_thermistor_platform_data *
 ptc_thermistor_parse_dt(struct device *dev)
 {
 	struct iio_channel *chan;
 	enum iio_chan_type type;
 	struct device_node *np = dev->of_node;
 	struct ptc_thermistor_platform_data *pdata;
 	int ret;

 	if (!np)
 		return NULL;

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

 	chan = devm_iio_channel_get(dev, NULL);
 	if (IS_ERR(chan))
 		return ERR_CAST(chan);

 	ret = iio_get_channel_type(chan, &type);
 	if (ret < 0)
 		return ERR_PTR(ret);

 	if (type != IIO_VOLTAGE)
 		return ERR_PTR(-EINVAL);

 	if (of_property_read_u32(np, "pullup-uv", &pdata->pullup_uv))
 		return ERR_PTR(-ENODEV);
 	if (of_property_read_u32(np, "pull-ohm", &pdata->pull_ohm))
 		return ERR_PTR(-ENODEV);

 	if (of_find_property(np, "connected-positive", NULL))
 		pdata->connect = PTC_CONNECTED_POSITIVE;
 	else /* status change should be possible if not always on. */
 		pdata->connect = PTC_CONNECTED_GROUND;

 	pdata->chan = chan;
 	pdata->read_uv = ptc_adc_iio_read;

 	return pdata;
 }
 #else
 static struct ptc_thermistor_platform_data *
 ptc_thermistor_parse_dt(struct device *dev)
 {
 	return NULL;
 }

 #define ptc_match	NULL

 #endif

 static inline u64 div64_u64_safe(u64 dividend, u64 divisor)
 {
 	if (divisor == 0 && dividend == 0)
 		return 0;
 	if (divisor == 0)
 		return UINT_MAX;
 	return div64_u64(dividend, divisor);
 }

 static int get_ohm_of_thermistor(struct ptc_data *data, unsigned int uv)
 {
 	struct ptc_thermistor_platform_data *pdata = data->pdata;
 	u32 puv = pdata->pullup_uv;
 	u64 n, po;

 	po = pdata->pull_ohm;

 	if (uv == 0)
 		return (pdata->connect == PTC_CONNECTED_POSITIVE) ?
 			INT_MAX : 0;
 	if (uv >= puv)
 		return (pdata->connect == PTC_CONNECTED_POSITIVE) ?
 			0 : INT_MAX;

 	if (pdata->connect == PTC_CONNECTED_POSITIVE)
 		n = div_u64(po * (puv - uv), uv);
 	else
 		n = div_u64(po * uv, puv - uv);

 	if (n > INT_MAX)
 		n = INT_MAX;
 	return n;
 }

 static void lookup_comp(struct ptc_data *data, unsigned int ohm,
 			int *i_low, int *i_high)
 {
 	int start, end, mid;

 	/*
 	 * Handle special cases: Resistance is higher than or equal to
 	 * resistance in first table entry, or resistance is lower or equal
 	 * to resistance in last table entry.
 	 * In these cases, return i_low == i_high, either pointing to the
 	 * beginning or to the end of the table depending on the condition.
 	 */
 	if (ohm >= data->comp[0].ohm) {
 		*i_low = 0;
 		*i_high = 0;
 		return;
 	}
 	if (ohm <= data->comp[data->n_comp - 1].ohm) {
 		*i_low = data->n_comp - 1;
 		*i_high = data->n_comp - 1;
 		return;
 	}

 	/* Do a binary search on compensation table */
 	start = 0;
 	end = data->n_comp;
 	while (start < end) {
 		mid = start + (end - start) / 2;
 		/*
 		 * start <= mid < end
 		 * data->comp[start].ohm > ohm >= data->comp[end].ohm
 		 *
 		 * We could check for "ohm == data->comp[mid].ohm" here, but
 		 * that is a quite unlikely condition, and we would have to
 		 * check again after updating start. Check it at the end instead
 		 * for simplicity.
 		 */
 		if (ohm >= data->comp[mid].ohm) {
 			end = mid;
 		} else {
 			start = mid + 1;
 			/*
 			 * ohm >= data->comp[start].ohm might be true here,
 			 * since we set start to mid + 1. In that case, we are
 			 * done. We could keep going, but the condition is quite
 			 * likely to occur, so it is worth checking for it.
 			 */
 			if (ohm >= data->comp[start].ohm)
 				end = start;
 		}
 		/*
 		 * start <= end
 		 * data->comp[start].ohm >= ohm >= data->comp[end].ohm
 		 */
 	}
 	/*
 	 * start == end
 	 * ohm >= data->comp[end].ohm
 	 */
 	*i_low = end;
 	if (ohm == data->comp[end].ohm)
 		*i_high = end;
 	else
 		*i_high = end - 1;
 }

 static int get_temp_mc(struct ptc_data *data, unsigned int ohm)
 {
 	int low, high;
 	int temp;

 	lookup_comp(data, ohm, &low, &high);
 	if (low == high) {
 		/* Unable to use linear approximation */
 		temp = data->comp[low].temp_c * 1000;
 	} else {
 		temp = data->comp[low].temp_c * 1000 +
 			((data->comp[high].temp_c - data->comp[low].temp_c) *
 			 1000 * ((int)ohm - (int)data->comp[low].ohm)) /
 			((int)data->comp[high].ohm - (int)data->comp[low].ohm);
 	}
 	return temp;
 }

 static int ptc_thermistor_get_ohm(struct ptc_data *data)
 {
 	int read_uv;

 	if (data->pdata->read_ohm)
 		return data->pdata->read_ohm();

 	if (data->pdata->read_uv) {
 		read_uv = data->pdata->read_uv(data->pdata);
 		if (read_uv < 0)
 			return read_uv;
 		return get_ohm_of_thermistor(data, read_uv);
 	}
 	return -EINVAL;
 }

 static int ptc_read_temp(void *data, int *temp)
 {
 	int ohm;

 	ohm = ptc_thermistor_get_ohm(data);
 	if (ohm < 0)
 		return ohm;

 	*temp = get_temp_mc(data, ohm);

 	return 0;
 }

 static ssize_t ptc_show_type(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
 	return sprintf(buf, "4\n");
 }

 static ssize_t ptc_show_temp(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
 	struct ptc_data *data = dev_get_drvdata(dev);
 	int ohm;

 	ohm = ptc_thermistor_get_ohm(data);
 	if (ohm < 0)
 		return ohm;

 	return sprintf(buf, "%d\n",
 			get_temp_mc(data, ohm) + data->offset_mc);
 }

 static ssize_t ptc_show_offset(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
 	struct ptc_data *data = dev_get_drvdata(dev);

 	return sprintf(buf, "%d\n", data->offset_mc);
 }

 static ssize_t ptc_store_offset(struct device *dev,
 		struct device_attribute *da, const char *buf, size_t count)
 {
 	struct ptc_data *data = dev_get_drvdata(dev);
 	int val;
 	int err;

 	err = kstrtoint(buf, 10, &val);
 	if (err)
 		return err;

 	data->offset_mc = val;
 	return count;
 }

 static SENSOR_DEVICE_ATTR(temp1_type, 0444, ptc_show_type, NULL, 0);
 static SENSOR_DEVICE_ATTR(temp1_input, 0444, ptc_show_temp, NULL, 0);
 static SENSOR_DEVICE_ATTR(temp1_offset,
 		0644, ptc_show_offset, ptc_store_offset, 0);

 static struct attribute *ptc_attrs[] = {
 	&sensor_dev_attr_temp1_type.dev_attr.attr,
 	&sensor_dev_attr_temp1_input.dev_attr.attr,
 	&sensor_dev_attr_temp1_offset.dev_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(ptc);

 static const struct thermal_zone_of_device_ops ptc_of_thermal_ops = {
 	.get_temp = ptc_read_temp,
 };

 static int ptc_thermistor_probe(struct platform_device *pdev)
 {
 	struct thermal_zone_device *tz;
 	struct device *dev = &pdev->dev;
 	const struct of_device_id *of_id =
 			of_match_device(of_match_ptr(ptc_match), dev);
 	const struct platform_device_id *pdev_id;
 	struct ptc_thermistor_platform_data *pdata;
 	struct device *hwmon_dev;
 	struct ptc_data *data;

 	pdata = ptc_thermistor_parse_dt(dev);
 	if (IS_ERR(pdata))
 		return PTR_ERR(pdata);
 	else if (!pdata)
 		pdata = dev_get_platdata(dev);

 	if (!pdata) {
 		dev_err(dev, "No platform init data supplied.\n");
 		return -ENODEV;
 	}

 	/* Either one of the two is required. */
 	if (!pdata->read_uv && !pdata->read_ohm) {
 		dev_err(dev,
 			"Both read_uv and read_ohm missing. Need either one of the two.\n");
 		return -EINVAL;
 	}

 	if (pdata->read_uv && pdata->read_ohm) {
 		dev_warn(dev,
 			 "Only one of read_uv and read_ohm is needed; ignoring read_uv.\n");
 		pdata->read_uv = NULL;
 	}

 	if (pdata->read_uv && (pdata->pullup_uv == 0 ||
 				pdata->pull_ohm == 0 ||
 				(pdata->connect != PTC_CONNECTED_POSITIVE &&
 				 pdata->connect != PTC_CONNECTED_GROUND))) {
 		dev_err(dev, "Required data to use read_uv not supplied.\n");
 		return -EINVAL;
 	}

 	data = devm_kzalloc(dev, sizeof(struct ptc_data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;

 	pdev_id = of_id ? of_id->data : platform_get_device_id(pdev);

 	data->pdata = pdata;
 	data->offset_mc = 0;

 	switch (pdev_id->driver_data) {
 	case TYPE_TMP6331DECR_VBIAS_1_8_V_100000_OHM:
 		data->comp = comp_tmp6331decr_vbias_1_8v_100000_ohm;
 		data->n_comp = ARRAY_SIZE(comp_tmp6331decr_vbias_1_8v_100000_ohm);
 		break;
 	default:
 		dev_err(dev, "Unknown device type: %lu(%s)\n",
 				pdev_id->driver_data, pdev_id->name);
 		return -EINVAL;
 	}

 	hwmon_dev = devm_hwmon_device_register_with_groups(dev, pdev_id->name,
 							   data, ptc_groups);
 	if (IS_ERR(hwmon_dev)) {
 		dev_err(dev, "unable to register as hwmon device.\n");
 		return PTR_ERR(hwmon_dev);
 	}

 	dev_info(dev, "Thermistor type: %s successfully probed.\n",
 		 pdev_id->name);

 	tz = devm_thermal_zone_of_sensor_register(dev, 0, data,
 						  &ptc_of_thermal_ops);
 	if (IS_ERR(tz))
 		dev_dbg(dev, "Failed to register to thermal fw.\n");

 	return 0;
 }

 static struct platform_driver ptc_thermistor_driver = {
 	.driver = {
 		.name = "ptc-thermistor",
 		.of_match_table = of_match_ptr(ptc_match),
 	},
 	.probe = ptc_thermistor_probe,
 	.id_table = ptc_thermistor_id,
 };

 module_platform_driver(ptc_thermistor_driver);

 MODULE_DESCRIPTION("PTC Thermistor Driver");
 MODULE_AUTHOR("Tang Lee <tanglee@google.com>");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("platform:ptc-thermistor");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* The driver is developed based on ntc_thermistor driver.
	*
	* Copyright 2020 Google LLC.
	*/

	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/pm_runtime.h>
	#include <linux/math64.h>
	#include <linux/platform_device.h>
	#include <linux/err.h>
	#include <linux/of.h>
	#include <linux/of_device.h>

	#include <linux/platform_data/ptc_thermistor.h>

	#include <linux/iio/iio.h>
	#include <linux/iio/machine.h>
	#include <linux/iio/driver.h>
	#include <linux/iio/consumer.h>

	#include <linux/hwmon.h>
	#include <linux/hwmon-sysfs.h>
	#include <linux/thermal.h>

	struct ptc_compensation {
	int temp_c;
	unsigned int ohm;
	};

	/* Order matters, ptc_match references the entries by index */
	static const struct platform_device_id ptc_thermistor_id[] = {
	{ "tmp6331decr,v,conf1", TYPE_TMP6331DECR_VBIAS_1_8_V_100000_OHM },
	{ },
	};

	/*
	* temp_c in descending order for PTC thermistors
	*/
	static const struct ptc_compensation comp_tmp6331decr_vbias_1_8v_100000_ohm[] = {
	{ .temp_c = 125, .ohm = 175288 },
	{ .temp_c = 120, .ohm = 170610 },
	{ .temp_c = 115, .ohm = 166029 },
	{ .temp_c = 110, .ohm = 161541 },
	{ .temp_c = 105, .ohm = 157146 },
	{ .temp_c = 100, .ohm = 152841 },
	{ .temp_c = 95, .ohm = 148626 },
	{ .temp_c = 90, .ohm = 144498 },
	{ .temp_c = 85, .ohm = 140457 },
	{ .temp_c = 80, .ohm = 136502 },
	{ .temp_c = 75, .ohm = 132630 },
	{ .temp_c = 70, .ohm = 128840 },
	{ .temp_c = 65, .ohm = 125133 },
	{ .temp_c = 60, .ohm = 121506 },
	{ .temp_c = 55, .ohm = 117958 },
	{ .temp_c = 50, .ohm = 114489 },
	{ .temp_c = 45, .ohm = 111098 },
	{ .temp_c = 40, .ohm = 107783 },
	{ .temp_c = 35, .ohm = 104545 },
	{ .temp_c = 30, .ohm = 101383 },
	{ .temp_c = 25, .ohm = 98295 },
	{ .temp_c = 20, .ohm = 95281 },
	{ .temp_c = 15, .ohm = 92342 },
	{ .temp_c = 10, .ohm = 89475 },
	{ .temp_c = 5, .ohm = 86682 },
	{ .temp_c = 0, .ohm = 83961 },
	{ .temp_c = -5, .ohm = 81312 },
	{ .temp_c = -10, .ohm = 78736 },
	{ .temp_c = -15, .ohm = 76232 },
	{ .temp_c = -20, .ohm = 73800 },
	{ .temp_c = -25, .ohm = 71439 },
	{ .temp_c = -30, .ohm = 69151 },
	{ .temp_c = -35, .ohm = 66935 },
	{ .temp_c = -40, .ohm = 64791 },
	};

	struct ptc_data {
	struct ptc_thermistor_platform_data *pdata;
	const struct ptc_compensation *comp;
	int n_comp;
	int offset_mc;
	};

	#if defined(CONFIG_OF) && IS_ENABLED(CONFIG_IIO)
	static int ptc_adc_iio_read(struct ptc_thermistor_platform_data *pdata)
	{
	struct iio_channel *channel = pdata->chan;
	int raw, uv, ret;

	ret = iio_read_channel_raw(channel, &raw);
	if (ret < 0) {
	pr_err("read channel() error: %d\n", ret);
	return ret;
	}

	ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
	if (ret < 0) {
	/* Assume 12 bit ADC with vref at pullup_uv */
	uv = (pdata->pullup_uv * (s64)raw) >> 12;
	}

	return uv;
	}

	static const struct of_device_id ptc_match[] = {
	{ .compatible = "ti,tmp6331decr,vbias-1.8v-100000ohm",
	.data = &ptc_thermistor_id[0] },
	{ },
	};
	MODULE_DEVICE_TABLE(of, ptc_match);

	static struct ptc_thermistor_platform_data *
	ptc_thermistor_parse_dt(struct device *dev)
	{
	struct iio_channel *chan;
	enum iio_chan_type type;
	struct device_node *np = dev->of_node;
	struct ptc_thermistor_platform_data *pdata;
	int ret;

	if (!np)
	return NULL;

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

	chan = devm_iio_channel_get(dev, NULL);
	if (IS_ERR(chan))
	return ERR_CAST(chan);

	ret = iio_get_channel_type(chan, &type);
	if (ret < 0)
	return ERR_PTR(ret);

	if (type != IIO_VOLTAGE)
	return ERR_PTR(-EINVAL);

	if (of_property_read_u32(np, "pullup-uv", &pdata->pullup_uv))
	return ERR_PTR(-ENODEV);
	if (of_property_read_u32(np, "pull-ohm", &pdata->pull_ohm))
	return ERR_PTR(-ENODEV);

	if (of_find_property(np, "connected-positive", NULL))
	pdata->connect = PTC_CONNECTED_POSITIVE;
	else /* status change should be possible if not always on. */
	pdata->connect = PTC_CONNECTED_GROUND;

	pdata->chan = chan;
	pdata->read_uv = ptc_adc_iio_read;

	return pdata;
	}
	#else
	static struct ptc_thermistor_platform_data *
	ptc_thermistor_parse_dt(struct device *dev)
	{
	return NULL;
	}

	#define ptc_match NULL

	#endif

	static inline u64 div64_u64_safe(u64 dividend, u64 divisor)
	{
	if (divisor == 0 && dividend == 0)
	return 0;
	if (divisor == 0)
	return UINT_MAX;
	return div64_u64(dividend, divisor);
	}

	static int get_ohm_of_thermistor(struct ptc_data *data, unsigned int uv)
	{
	struct ptc_thermistor_platform_data *pdata = data->pdata;
	u32 puv = pdata->pullup_uv;
	u64 n, po;

	po = pdata->pull_ohm;

	if (uv == 0)
	return (pdata->connect == PTC_CONNECTED_POSITIVE) ?
	INT_MAX : 0;
	if (uv >= puv)
	return (pdata->connect == PTC_CONNECTED_POSITIVE) ?
	0 : INT_MAX;

	if (pdata->connect == PTC_CONNECTED_POSITIVE)
	n = div_u64(po * (puv - uv), uv);
	else
	n = div_u64(po * uv, puv - uv);

	if (n > INT_MAX)
	n = INT_MAX;
	return n;
	}

	static void lookup_comp(struct ptc_data *data, unsigned int ohm,
	int i_low, int i_high)
	{
	int start, end, mid;

	/*
	* Handle special cases: Resistance is higher than or equal to
	* resistance in first table entry, or resistance is lower or equal
	* to resistance in last table entry.
	* In these cases, return i_low == i_high, either pointing to the
	* beginning or to the end of the table depending on the condition.
	*/
	if (ohm >= data->comp[0].ohm) {
	*i_low = 0;
	*i_high = 0;
	return;
	}
	if (ohm <= data->comp[data->n_comp - 1].ohm) {
	*i_low = data->n_comp - 1;
	*i_high = data->n_comp - 1;
	return;
	}

	/* Do a binary search on compensation table */
	start = 0;
	end = data->n_comp;
	while (start < end) {
	mid = start + (end - start) / 2;
	/*
	* start <= mid < end
	* data->comp[start].ohm > ohm >= data->comp[end].ohm
	*
	* We could check for "ohm == data->comp[mid].ohm" here, but
	* that is a quite unlikely condition, and we would have to
	* check again after updating start. Check it at the end instead
	* for simplicity.
	*/
	if (ohm >= data->comp[mid].ohm) {
	end = mid;
	} else {
	start = mid + 1;
	/*
	* ohm >= data->comp[start].ohm might be true here,
	* since we set start to mid + 1. In that case, we are
	* done. We could keep going, but the condition is quite
	* likely to occur, so it is worth checking for it.
	*/
	if (ohm >= data->comp[start].ohm)
	end = start;
	}
	/*
	* start <= end
	* data->comp[start].ohm >= ohm >= data->comp[end].ohm
	*/
	}
	/*
	* start == end
	* ohm >= data->comp[end].ohm
	*/
	*i_low = end;
	if (ohm == data->comp[end].ohm)
	*i_high = end;
	else
	*i_high = end - 1;
	}

	static int get_temp_mc(struct ptc_data *data, unsigned int ohm)
	{
	int low, high;
	int temp;

	lookup_comp(data, ohm, &low, &high);
	if (low == high) {
	/* Unable to use linear approximation */
	temp = data->comp[low].temp_c * 1000;
	} else {
	temp = data->comp[low].temp_c * 1000 +
	((data->comp[high].temp_c - data->comp[low].temp_c) *
	1000 * ((int)ohm - (int)data->comp[low].ohm)) /
	((int)data->comp[high].ohm - (int)data->comp[low].ohm);
	}
	return temp;
	}

	static int ptc_thermistor_get_ohm(struct ptc_data *data)
	{
	int read_uv;

	if (data->pdata->read_ohm)
	return data->pdata->read_ohm();

	if (data->pdata->read_uv) {
	read_uv = data->pdata->read_uv(data->pdata);
	if (read_uv < 0)
	return read_uv;
	return get_ohm_of_thermistor(data, read_uv);
	}
	return -EINVAL;
	}

	static int ptc_read_temp(void data, int temp)
	{
	int ohm;

	ohm = ptc_thermistor_get_ohm(data);
	if (ohm < 0)
	return ohm;

	*temp = get_temp_mc(data, ohm);

	return 0;
	}

	static ssize_t ptc_show_type(struct device *dev,
	struct device_attribute attr, char buf)
	{
	return sprintf(buf, "4\n");
	}

	static ssize_t ptc_show_temp(struct device *dev,
	struct device_attribute attr, char buf)
	{
	struct ptc_data *data = dev_get_drvdata(dev);
	int ohm;

	ohm = ptc_thermistor_get_ohm(data);
	if (ohm < 0)
	return ohm;

	return sprintf(buf, "%d\n",
	get_temp_mc(data, ohm) + data->offset_mc);
	}

	static ssize_t ptc_show_offset(struct device *dev,
	struct device_attribute attr, char buf)
	{
	struct ptc_data *data = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", data->offset_mc);
	}

	static ssize_t ptc_store_offset(struct device *dev,
	struct device_attribute da, const char buf, size_t count)
	{
	struct ptc_data *data = dev_get_drvdata(dev);
	int val;
	int err;

	err = kstrtoint(buf, 10, &val);
	if (err)
	return err;

	data->offset_mc = val;
	return count;
	}

	static SENSOR_DEVICE_ATTR(temp1_type, 0444, ptc_show_type, NULL, 0);
	static SENSOR_DEVICE_ATTR(temp1_input, 0444, ptc_show_temp, NULL, 0);
	static SENSOR_DEVICE_ATTR(temp1_offset,
	0644, ptc_show_offset, ptc_store_offset, 0);

	static struct attribute *ptc_attrs[] = {
	&sensor_dev_attr_temp1_type.dev_attr.attr,
	&sensor_dev_attr_temp1_input.dev_attr.attr,
	&sensor_dev_attr_temp1_offset.dev_attr.attr,
	NULL,
	};
	ATTRIBUTE_GROUPS(ptc);

	static const struct thermal_zone_of_device_ops ptc_of_thermal_ops = {
	.get_temp = ptc_read_temp,
	};

	static int ptc_thermistor_probe(struct platform_device *pdev)
	{
	struct thermal_zone_device *tz;
	struct device *dev = &pdev->dev;
	const struct of_device_id *of_id =
	of_match_device(of_match_ptr(ptc_match), dev);
	const struct platform_device_id *pdev_id;
	struct ptc_thermistor_platform_data *pdata;
	struct device *hwmon_dev;
	struct ptc_data *data;

	pdata = ptc_thermistor_parse_dt(dev);
	if (IS_ERR(pdata))
	return PTR_ERR(pdata);
	else if (!pdata)
	pdata = dev_get_platdata(dev);

	if (!pdata) {
	dev_err(dev, "No platform init data supplied.\n");
	return -ENODEV;
	}

	/* Either one of the two is required. */
	if (!pdata->read_uv && !pdata->read_ohm) {
	dev_err(dev,
	"Both read_uv and read_ohm missing. Need either one of the two.\n");
	return -EINVAL;
	}

	if (pdata->read_uv && pdata->read_ohm) {
	dev_warn(dev,
	"Only one of read_uv and read_ohm is needed; ignoring read_uv.\n");
	pdata->read_uv = NULL;
	}

	if (pdata->read_uv && (pdata->pullup_uv == 0 \|\|
	pdata->pull_ohm == 0 \|\|
	(pdata->connect != PTC_CONNECTED_POSITIVE &&
	pdata->connect != PTC_CONNECTED_GROUND))) {
	dev_err(dev, "Required data to use read_uv not supplied.\n");
	return -EINVAL;
	}

	data = devm_kzalloc(dev, sizeof(struct ptc_data), GFP_KERNEL);
	if (!data)
	return -ENOMEM;

	pdev_id = of_id ? of_id->data : platform_get_device_id(pdev);

	data->pdata = pdata;
	data->offset_mc = 0;

	switch (pdev_id->driver_data) {
	case TYPE_TMP6331DECR_VBIAS_1_8_V_100000_OHM:
	data->comp = comp_tmp6331decr_vbias_1_8v_100000_ohm;
	data->n_comp = ARRAY_SIZE(comp_tmp6331decr_vbias_1_8v_100000_ohm);
	break;
	default:
	dev_err(dev, "Unknown device type: %lu(%s)\n",
	pdev_id->driver_data, pdev_id->name);
	return -EINVAL;
	}

	hwmon_dev = devm_hwmon_device_register_with_groups(dev, pdev_id->name,
	data, ptc_groups);
	if (IS_ERR(hwmon_dev)) {
	dev_err(dev, "unable to register as hwmon device.\n");
	return PTR_ERR(hwmon_dev);
	}

	dev_info(dev, "Thermistor type: %s successfully probed.\n",
	pdev_id->name);

	tz = devm_thermal_zone_of_sensor_register(dev, 0, data,
	&ptc_of_thermal_ops);
	if (IS_ERR(tz))
	dev_dbg(dev, "Failed to register to thermal fw.\n");

	return 0;
	}

	static struct platform_driver ptc_thermistor_driver = {
	.driver = {
	.name = "ptc-thermistor",
	.of_match_table = of_match_ptr(ptc_match),
	},
	.probe = ptc_thermistor_probe,
	.id_table = ptc_thermistor_id,
	};

	module_platform_driver(ptc_thermistor_driver);

	MODULE_DESCRIPTION("PTC Thermistor Driver");
	MODULE_AUTHOR("Tang Lee <tanglee@google.com>");
	MODULE_LICENSE("GPL");
	MODULE_ALIAS("platform:ptc-thermistor");