Commit dbe43a62 authored by Guenter Roeck's avatar Guenter Roeck
Browse files

hwmon: (ntc_thermistor) Optimize and fix build warning 



The following build warning is seen in some configurations:

drivers/hwmon/ntc_thermistor.c: In function 'ntc_show_temp':
drivers/hwmon/ntc_thermistor.c:293: warning: 'temp' may be used uninitialized in this function

Fix the problem by re-arranging the code to overload return values with error
codes, and by avoiding error returns whenever possible.

Specifically,

Simplify lookup_comp() to not return an error. Instead, return i_low == i_high
if there is an exact match, or if the ohm value is outside the lookup table
range.

Modify get_temp_mC() to not return an error. Since it only returns an error
after lookup_comp() returned an error, this is quite straightforward after above
change.

Separate ntc_thermistor_read() into a function to read the resistor value (which
can return an error), and the call to get_temp_mC() which doesn't. Call the
functions directly from ntc_show_temp().

Code was tested using a test program, comparing the result of the old and new
versions of get_temp_mC() for resistor values between 0 and 2,000,000 ohm.

As a side effect, this patch reduces code size by approximately 400 bytes on
x86_64.

Signed-off-by: default avatarGuenter Roeck <guenter.roeck@ericsson.com>
Cc: Donggeun Kim <dg77.kim@samsung.com>
Reviewed-by: default avatarRobert Coulson <robert.coulson@ericsson.com>
parent 425d2476

drivers/hwmon/ntc_thermistor.c

+80 −84
Original line number Diff line number Diff line
@@ -134,8 +134,7 @@ static inline u64 div64_u64_safe(u64 dividend, u64 divisor) 
	return div64_u64(dividend, divisor);

}



static unsigned int get_ohm_of_thermistor(struct ntc_data *data,

		unsigned int uV)

static int get_ohm_of_thermistor(struct ntc_data *data, unsigned int uV)

{

	struct ntc_thermistor_platform_data *pdata = data->pdata;

	u64 mV = uV / 1000;
@@ -146,12 +145,12 @@ static unsigned int get_ohm_of_thermistor(struct ntc_data *data, 


	if (mV == 0) {

		if (pdata->connect == NTC_CONNECTED_POSITIVE)

			return UINT_MAX;

			return INT_MAX;

		return 0;

	}

	if (mV >= pmV)

		return (pdata->connect == NTC_CONNECTED_POSITIVE) ?

			0 : UINT_MAX;

			0 : INT_MAX;



	if (pdata->connect == NTC_CONNECTED_POSITIVE && puO == 0)

		N = div64_u64_safe(pdO * (pmV - mV), mV);
@@ -163,113 +162,109 @@ static unsigned int get_ohm_of_thermistor(struct ntc_data *data, 
	else

		N = div64_u64_safe(pdO * puO * mV, pdO * (pmV - mV) - puO * mV);



	return (unsigned int) N;

	if (N > INT_MAX)

		N = INT_MAX;

	return N;

}



static int lookup_comp(struct ntc_data *data,

		unsigned int ohm, int *i_low, int *i_high)

static void lookup_comp(struct ntc_data *data, unsigned int ohm,

			int *i_low, int *i_high)

{

	int start, end, mid = -1;

	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 (end > start) {

	while (start < end) {

		mid = start + (end - start) / 2;

		if (data->comp[mid].ohm < ohm)

		/*

		 * 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 if (data->comp[mid].ohm > ohm)

			start = mid + 1;

		else

			break;

	}



	if (mid == 0) {

		if (data->comp[mid].ohm > ohm) {

			*i_high = mid;

			*i_low = mid + 1;

			return 0;

		} else {

			*i_low = mid;

			*i_high = -1;

			return -EINVAL;

		}

	}

	if (mid == (data->n_comp - 1)) {

		if (data->comp[mid].ohm <= ohm) {

			*i_low = mid;

			*i_high = mid - 1;

			return 0;

		} else {

			*i_low = -1;

			*i_high = mid;

			return -EINVAL;

		}

			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;

		}



	if (data->comp[mid].ohm <= ohm) {

		*i_low = mid;

		*i_high = mid - 1;

	} else {

		*i_low = mid + 1;

		*i_high = mid;

		/*

		 * start <= end

		 * data->comp[start].ohm >= ohm >= data->comp[end].ohm

		 */

	}



	return 0;

	/*

	 * 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 ntc_data *data, unsigned int ohm, int *temp)

static int get_temp_mC(struct ntc_data *data, unsigned int ohm)

{

	int low, high;

	int ret;

	int temp;



	ret = lookup_comp(data, ohm, &low, &high);

	if (ret) {

	lookup_comp(data, ohm, &low, &high);

	if (low == high) {

		/* Unable to use linear approximation */

		if (low != -1)

			*temp = data->comp[low].temp_C * 1000;

		else if (high != -1)

			*temp = data->comp[high].temp_C * 1000;

		else

			return ret;

		temp = data->comp[low].temp_C * 1000;

	} else {

		*temp = data->comp[low].temp_C * 1000 +

		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 0;

	return temp;

}



static int ntc_thermistor_read(struct ntc_data *data, int *temp)

static int ntc_thermistor_get_ohm(struct ntc_data *data)

{

	int ret;

	int read_ohm, read_uV;

	unsigned int ohm = 0;



	if (data->pdata->read_ohm) {

		read_ohm = data->pdata->read_ohm();

		if (read_ohm < 0)

			return read_ohm;

		ohm = (unsigned int)read_ohm;

	}

	int read_uV;



	if (data->pdata->read_ohm)

		return data->pdata->read_ohm();



	if (data->pdata->read_uV) {

		read_uV = data->pdata->read_uV();

		if (read_uV < 0)

			return read_uV;

		ohm = get_ohm_of_thermistor(data, (unsigned int)read_uV);

	}



	ret = get_temp_mC(data, ohm, temp);

	if (ret) {

		dev_dbg(data->dev, "Sensor reading function not available.\n");

		return ret;

		return get_ohm_of_thermistor(data, read_uV);

	}



	return 0;

	return -EINVAL;

}



static ssize_t ntc_show_name(struct device *dev,
@@ -290,12 +285,13 @@ static ssize_t ntc_show_temp(struct device *dev, 
		struct device_attribute *attr, char *buf)

{

	struct ntc_data *data = dev_get_drvdata(dev);

	int temp, ret;

	int ohm;



	ret = ntc_thermistor_read(data, &temp);

	if (ret)

		return ret;

	return sprintf(buf, "%d\n", temp);

	ohm = ntc_thermistor_get_ohm(data);

	if (ohm < 0)

		return ohm;



	return sprintf(buf, "%d\n", get_temp_mC(data, ohm));

}



static SENSOR_DEVICE_ATTR(temp1_type, S_IRUGO, ntc_show_type, NULL, 0);

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