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SubjectRe: [PATCH] hwmon: (ads7828) Enable internal reference
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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, &regval);
> +
> hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
> data,
> ads7828_groups);
>

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