4.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Akshay Bhat <akshay.bhat@xxxxxxxxxxx> commit 7a18afe8097731b8ffb6cb5b2b3b418ded77c105 upstream. On ads7828 the internal reference defaults to off upon power up. When using internal reference, it needs to be turned on and the voltage needs to settle before normal conversion cycle can be started. Hence perform a dummy read in the probe to enable the internal reference allowing the voltage to settle before performing a normal read. Without this fix, the first read from the ADC when using internal reference always returns incorrect data. Signed-off-by: Akshay Bhat <akshay.bhat@xxxxxxxxxxx> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/hwmon/ads7828.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/drivers/hwmon/ads7828.c +++ b/drivers/hwmon/ads7828.c @@ -120,6 +120,7 @@ static int ads7828_probe(struct i2c_clie unsigned int vref_mv = ADS7828_INT_VREF_MV; bool diff_input = false; bool ext_vref = false; + unsigned int regval; data = devm_kzalloc(dev, sizeof(struct ads7828_data), GFP_KERNEL); if (!data) @@ -154,6 +155,15 @@ static int ads7828_probe(struct i2c_clie if (!diff_input) data->cmd_byte |= ADS7828_CMD_SD_SE; + /* + * Datasheet specifies internal reference voltage is disabled by + * default. The internal reference voltage needs to be enabled and + * voltage needs to settle before getting valid ADC data. So perform a + * dummy read to enable the internal reference voltage. + */ + if (!ext_vref) + regmap_read(data->regmap, data->cmd_byte, ®val); + hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, data, ads7828_groups); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html