TMP102 works based on conversions done periodically. However, as per the TMP102 data sheet[1] the first conversion is triggered immediately after we program the configuration register. The temperature data registers do not reflect proper data until the first conversion is complete (in our case HZ/4). The driver currently sets the last_update to be jiffies - HZ, just after the configuration is complete. When TMP102 driver registers with the thermal framework, it immediately tries to read the sensor temperature data. This takes place even before the conversion on the TMP102 is complete and results in an invalid temperature read. Depending on the value read, this may cause thermal framework to assume that a critical temperature event has occurred and attempts to shutdown the system. Instead of causing an invalid mid-conversion value to be read erroneously, we mark the last_update to be in-line with the current jiffies. This allows the tmp102_update_device function to skip update until the required conversion time is complete. Further, we ensure to return -EAGAIN result instead of returning spurious temperature (such as 0C) values to the caller to prevent any wrong decisions made with such values. NOTE: this allows the read functions not to be blocking and allows the callers to make the decision if they would like to block or try again later. At least the current user(thermal) seems to handle this by retrying later. A simpler alternative approach could be to sleep in the probe for the duration required, but that will result in latency that is undesirable and delay boot sequence un-necessarily. [1] http://www.ti.com/lit/ds/symlink/tmp102.pdf Cc: Eduardo Valentin <edubezval@xxxxxxxxx> Reported-by: Aparna Balasubramanian <aparnab@xxxxxx> Reported-by: Elvita Lobo <elvita@xxxxxx> Reported-by: Yan Liu <yan-liu@xxxxxx> Signed-off-by: Nishanth Menon <nm@xxxxxx> --- Changes in V2 since V1: - Dropped out-of-range temperature used as a marker for first time we are using a bool now - minor update in comments to explain -EAGAIN return V1: https://patchwork.kernel.org/patch/7732781/ https://patchwork.kernel.org/patch/7737771/ Example case (from Beagleboard-x15 using an older kernel revision): http://pastebin.ubuntu.com/13591711/ Notice the thermal shutdown trigger: thermal thermal_zone3: critical temperature reached(108 C),shutting down drivers/hwmon/tmp102.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/drivers/hwmon/tmp102.c b/drivers/hwmon/tmp102.c index 65482624ea2c..5289aa0980a8 100644 --- a/drivers/hwmon/tmp102.c +++ b/drivers/hwmon/tmp102.c @@ -58,6 +58,7 @@ struct tmp102 { u16 config_orig; unsigned long last_update; int temp[3]; + bool first_time; }; /* convert left adjusted 13-bit TMP102 register value to milliCelsius */ @@ -93,6 +94,7 @@ static struct tmp102 *tmp102_update_device(struct device *dev) tmp102->temp[i] = tmp102_reg_to_mC(status); } tmp102->last_update = jiffies; + tmp102->first_time = false; } mutex_unlock(&tmp102->lock); return tmp102; @@ -102,6 +104,12 @@ static int tmp102_read_temp(void *dev, int *temp) { struct tmp102 *tmp102 = tmp102_update_device(dev); + /* Is it too early even to return a conversion? */ + if (tmp102->first_time) { + dev_dbg(dev, "%s: Conversion not ready yet..\n", __func__); + return -EAGAIN; + } + *temp = tmp102->temp[0]; return 0; @@ -114,6 +122,10 @@ static ssize_t tmp102_show_temp(struct device *dev, struct sensor_device_attribute *sda = to_sensor_dev_attr(attr); struct tmp102 *tmp102 = tmp102_update_device(dev); + /* Is it too early even to return a read? */ + if (tmp102->first_time) + return -EAGAIN; + return sprintf(buf, "%d\n", tmp102->temp[sda->index]); } @@ -207,7 +219,9 @@ static int tmp102_probe(struct i2c_client *client, status = -ENODEV; goto fail_restore_config; } - tmp102->last_update = jiffies - HZ; + tmp102->last_update = jiffies; + /* Mark that we are not ready with data until conversion is complete */ + tmp102->first_time = true; mutex_init(&tmp102->lock); hwmon_dev = hwmon_device_register_with_groups(dev, client->name, -- 2.6.2.402.g2635c2b _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
