iio: adc: ti-ads1015: avoid getting stale result after runtime resume

This driver assumes that the device is operating in the continuous
conversion mode which performs the conversion continuously.  So this driver
doesn't insert a wait time before reading the conversion register if the
configuration is not changed from a previous request.

This assumption is broken if the device is runtime suspended and entered
a power-down state.  The forthcoming request causes reading a stale result
from the conversion register as the device is runtime resumed just before.

Fix it by adding a flag to detect that condition and insert a necessary
wait time.

Cc: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/ti-ads1015.c b/drivers/iio/adc/ti-ads1015.c
index 9d77e837c09b5c2cd5e563d27261b8afa8ea4aa7..2f52b149f49a92b541a2a58f1672beb16a1f8a7f 100644 (file)
--- a/drivers/iio/adc/ti-ads1015.c
+++ b/drivers/iio/adc/ti-ads1015.c
@@ -177,6 +177,12 @@ struct ads1015_data {
        struct ads1015_channel_data channel_data[ADS1015_CHANNELS];
 
        unsigned int *data_rate;
+       /*
+        * Set to true when the ADC is switched to the continuous-conversion
+        * mode and exits from a power-down state.  This flag is used to avoid
+        * getting the stale result from the conversion register.
+        */
+       bool conv_invalid;
 };
 
 static bool ads1015_is_writeable_reg(struct device *dev, unsigned int reg)
@@ -255,9 +261,10 @@ int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val)
        if (ret < 0)
                return ret;
 
-       if (change) {
+       if (change || data->conv_invalid) {
                conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
                usleep_range(conv_time, conv_time + 1);
+               data->conv_invalid = false;
        }
 
        return regmap_read(data->regmap, ADS1015_CONV_REG, val);
@@ -630,6 +637,8 @@ static int ads1015_probe(struct i2c_client *client,
        if (ret)
                return ret;
 
+       data->conv_invalid = true;
+
        ret = pm_runtime_set_active(&client->dev);
        if (ret)
                goto err_buffer_cleanup;
@@ -685,10 +694,15 @@ static int ads1015_runtime_resume(struct device *dev)
 {
        struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
        struct ads1015_data *data = iio_priv(indio_dev);
+       int ret;
 
-       return regmap_update_bits(data->regmap, ADS1015_CFG_REG,
+       ret = regmap_update_bits(data->regmap, ADS1015_CFG_REG,
                                  ADS1015_CFG_MOD_MASK,
                                  ADS1015_CONTINUOUS << ADS1015_CFG_MOD_SHIFT);
+       if (!ret)
+               data->conv_invalid = true;
+
+       return ret;
 }
 #endif