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authorAkshay Bhat <akshay.bhat@timesys.com>2016-04-18 15:47:53 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-06-07 18:14:34 -0700
commitb8562066d4819ee23d3f8da2fa5e9160bf854835 (patch)
tree9f1ffdb09fe6b14017da00a7a815d99ec5aae258
parent9a11bd2d14ad54e92170cdc9c2e2f278305929c1 (diff)
hwmon: (ads7828) Enable internal reference
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@timesys.com> Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/hwmon/ads7828.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/hwmon/ads7828.c b/drivers/hwmon/ads7828.c
index 6c99ee7bafa3..ee396ff167d9 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 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, &regval);
+
hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
data,
ads7828_groups);