[PATCH] hwmon: (tmp108) Fix initial conversion delay and wait until ready

[PATCH] hwmon: (tmp108) Fix initial conversion delay and wait until ready

[Guenter Roeck]

In tmp108_common_probe(), the driver only adds the 30 ms conversion delay
(TMP108_CONVERSION_TIME_MS) to ready_time if the sensor was previously in
TMP108_MODE_SHUTDOWN. However, the TMP108 hardware defaults to continuous
conversion mode (TMP108_MODE_CONTINUOUS) upon power-on reset, including
immediately after enabling the vcc supply regulator during probe, while
the temperature register retains its power-on reset value of 0x0000 (0°C)
until the first conversion completes. Because the initial mode is not
shutdown, the delay is bypassed and early reads via thermal zone
registration or sysfs before the first conversion finishes return an
uninitialized 0°C reading.

In addition, returning -EAGAIN from tmp108_read() while waiting for a
conversion to complete after probe or resume can trigger an unnecessary
tight retry loop in callers or fail initial reads.

Unconditionally set ready_time to TMP108_CONVERSION_TIME_MS ahead in
tmp108_common_probe(), track ready_time as ktime_t, and wait for the
remaining conversion time in tmp108_read() using usleep_range() instead
of returning -EAGAIN.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 66e1c9171339 ("hwmon: Add Texas Instruments TMP108 temperature sensor driver.")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/tmp108.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/drivers/hwmon/tmp108.c b/drivers/hwmon/tmp108.c
index 91d20a1ce112..862b944d3e60 100644
--- a/drivers/hwmon/tmp108.c
+++ b/drivers/hwmon/tmp108.c
@@ -13,7 +13,7 @@
 #include <linux/i2c.h>
 #include <linux/i3c/device.h>
 #include <linux/init.h>
-#include <linux/jiffies.h>
+#include <linux/ktime.h>
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
@@ -78,7 +78,7 @@
 struct tmp108 {
 	struct regmap *regmap;
 	u16 orig_config;
-	u64 ready_time;
+	ktime_t ready_time;
 	const struct tmp108_params *params;
 };
 
@@ -121,6 +121,7 @@ static int tmp108_read(struct device *dev, enum hwmon_sensor_types type,
 	struct tmp108 *tmp108 = dev_get_drvdata(dev);
 	unsigned int regval;
 	int err, hyst;
+	s64 delay;
 
 	if (type == hwmon_chip) {
 		if (attr == hwmon_chip_update_interval) {
@@ -137,12 +138,10 @@ static int tmp108_read(struct device *dev, enum hwmon_sensor_types type,
 
 	switch (attr) {
 	case hwmon_temp_input:
-		/* Is it too early to return a conversion ? */
-		if (time_before64(get_jiffies_64(), tmp108->ready_time)) {
-			dev_dbg(dev, "%s: Conversion not ready yet..\n",
-				__func__);
-			return -EAGAIN;
-		}
+		/* Wait if it is too early to return a conversion */
+		delay = ktime_us_delta(tmp108->ready_time, ktime_get());
+		if (delay > 0)
+			usleep_range(delay, delay + 1000);
 		err = regmap_read(tmp108->regmap, TMP108_REG_TEMP, &regval);
 		if (err < 0)
 			return err;
@@ -477,11 +476,8 @@ static int tmp108_common_probe(struct device *dev, struct regmap *regmap, char *
 		return err;
 	}
 
-	tmp108->ready_time = get_jiffies_64();
-	if ((tmp108->orig_config & TMP108_CONF_MODE_MASK) ==
-	    TMP108_MODE_SHUTDOWN)
-		tmp108->ready_time +=
-			msecs_to_jiffies(TMP108_CONVERSION_TIME_MS);
+	tmp108->ready_time = ktime_add_ms(ktime_get(),
+					  TMP108_CONVERSION_TIME_MS);
 
 	err = devm_add_action_or_reset(dev, tmp108_restore_config, tmp108);
 	if (err) {
@@ -528,8 +524,8 @@ static int tmp108_resume(struct device *dev)
 
 	err = regmap_update_bits(tmp108->regmap, TMP108_REG_CONF,
 				 TMP108_CONF_MODE_MASK, TMP108_MODE_CONTINUOUS);
-	tmp108->ready_time = get_jiffies_64() +
-			     msecs_to_jiffies(TMP108_CONVERSION_TIME_MS);
+	tmp108->ready_time = ktime_add_ms(ktime_get(),
+					  TMP108_CONVERSION_TIME_MS);
 	return err;
 }
 
-- 
2.45.2

Re: [PATCH] hwmon: (tmp108) Fix initial conversion delay and wait until ready

[sashiko-bot]

> In tmp108_common_probe(), the driver only adds the 30 ms conversion delay
> (TMP108_CONVERSION_TIME_MS) to ready_time if the sensor was previously in
> TMP108_MODE_SHUTDOWN. However, the TMP108 hardware defaults to continuous
> conversion mode (TMP108_MODE_CONTINUOUS) upon power-on reset, including
> immediately after enabling the vcc supply regulator during probe, while
> the temperature register retains its power-on reset value of 0x0000 (0°C)
> until the first conversion completes. Because the initial mode is not
> shutdown, the delay is bypassed and early reads via thermal zone
> registration or sysfs before the first conversion finishes return an
> uninitialized 0°C reading.
> 
> In addition, returning -EAGAIN from tmp108_read() while waiting for a
> conversion to complete after probe or resume can trigger an unnecessary
> tight retry loop in callers or fail initial reads.
> 
> Unconditionally set ready_time to TMP108_CONVERSION_TIME_MS ahead in
> tmp108_common_probe(), track ready_time as ktime_t, and wait for the
> remaining conversion time in tmp108_read() using usleep_range() instead
> of returning -EAGAIN.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Fixes: 66e1c9171339 ("hwmon: Add Texas Instruments TMP108 temperature sensor driver.")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261031034834.1079813-1-linux@roeck-us.net?part=1