| Message ID | 1461008873-17694-1-git-send-email-akshay.bhat@timesys.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On 04/18/2016 12:47 PM, Akshay Bhat wrote: > 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@timesys.com> Applied (after fixing 'volatage' in the comment below). Thanks, Guenter > --- > drivers/hwmon/ads7828.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/hwmon/ads7828.c b/drivers/hwmon/ads7828.c > index 6c99ee7..b15c9bd 100644 > --- a/drivers/hwmon/ads7828.c > +++ b/drivers/hwmon/ads7828.c > @@ -120,6 +120,7 @@ static int ads7828_probe(struct i2c_client *client, > 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_client *client, > if (!diff_input) > data->cmd_byte |= ADS7828_CMD_SD_SE; > > + /* > + * Datasheet specifies internal reference volatage 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 linux-hwmon" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/hwmon/ads7828.c b/drivers/hwmon/ads7828.c index 6c99ee7..b15c9bd 100644 --- a/drivers/hwmon/ads7828.c +++ b/drivers/hwmon/ads7828.c @@ -120,6 +120,7 @@ static int ads7828_probe(struct i2c_client *client, 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_client *client, if (!diff_input) data->cmd_byte |= ADS7828_CMD_SD_SE; + /* + * Datasheet specifies internal reference volatage 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);
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@timesys.com> --- drivers/hwmon/ads7828.c | 10 ++++++++++ 1 file changed, 10 insertions(+)