[PATCH 4.12 13/43] iio: adc: ti-ads1015: avoid getting stale result after runtime resume - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Daniel Baluta <daniel.baluta@gmail.com>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>
Subject: [PATCH 4.12 13/43] iio: adc: ti-ads1015: avoid getting stale result after runtime resume
Date: Fri,  8 Sep 2017 15:19:01 +0200	[thread overview]
Message-ID: <20170908131827.057083487@linuxfoundation.org> (raw)
In-Reply-To: <20170908131826.555428826@linuxfoundation.org>

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Akinobu Mita <akinobu.mita@gmail.com>

commit 73e3e3fc50de50cfd68e945d85679c983ed31bd9 upstream.

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>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/iio/adc/ti-ads1015.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

--- 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 ads101
 	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_clie
 	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
 {
 	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
 
