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: Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>
Cc: Donggeun Kim <dg77.kim@xxxxxxxxxxx>
---
drivers/hwmon/ntc_thermistor.c | 164 +++++++++++++++++++--------------------
1 files changed, 80 insertions(+), 84 deletions(-)
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 9b382ec..d06e354 100644
--- a/drivers/hwmon/ntc_thermistor.c
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -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;
}
+ /*
+ * start <= end
+ * data->comp[start].ohm >= ohm >= data->comp[end].ohm
+ */
}
-
- if (data->comp[mid].ohm <= ohm) {
- *i_low = mid;
- *i_high = mid - 1;
- } else {
- *i_low = mid + 1;
- *i_high = mid;
- }
-
- 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);
+ return get_ohm_of_thermistor(data, read_uV);
}
-
- ret = get_temp_mC(data, ohm, temp);
- if (ret) {
- dev_dbg(data->dev, "Sensor reading function not available.\n");
- return ret;
- }
-
- 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;
+
+ ohm = ntc_thermistor_get_ohm(data);
+ if (ohm < 0)
+ return ohm;
- ret = ntc_thermistor_read(data, &temp);
- if (ret)
- return ret;
- return sprintf(buf, "%d\n", temp);
+ return sprintf(buf, "%d\n", get_temp_mC(data, ohm));
}
static SENSOR_DEVICE_ATTR(temp1_type, S_IRUGO, ntc_show_type, NULL, 0);
--
1.7.9.48.g85da4d
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