Patch "iio: adc: ti-ads1015: add adequate wait time to get correct conversion" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

iio: adc: ti-ads1015: add adequate wait time to get correct conversion

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iio-adc-ti-ads1015-add-adequate-wait-time-to-get-correct-conversion.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Akinobu Mita <[email protected]>
Date: Fri, 21 Jul 2017 00:24:22 +0900
Subject: iio: adc: ti-ads1015: add adequate wait time to get correct conversion

From: Akinobu Mita <[email protected]>

commit 4744d4e2afebf9644a439da9ca73d822fdd67bd9 upstream.

This driver assumes that the device is operating in the continuous conversion mode which performs the conversion continuously. So this driver inserts a wait time before reading the conversion register if the configuration is changed from a previous request.

Currently, the wait time is only the period required for a single conversion that is calculated as the reciprocal of the sampling frequency. However we also need to wait for the the previous conversion to complete. Otherwise we probably get the conversion result for the previous configuration when the sampling frequency is lower.

---
 drivers/iio/adc/ti-ads1015.c |   31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

@@ -241,27 +241,34 @@ static
 int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val)
 {
 	int ret, pga, dr, conv_time;
-	bool change;
+	unsigned int old, mask, cfg;
 
 	if (chan < 0 || chan >= ADS1015_CHANNELS)
 		return -EINVAL;
 
+	ret = regmap_read(data->regmap, ADS1015_CFG_REG, &old);
+	if (ret)
+		return ret;
+
 	pga = data->channel_data[chan].pga;
 	dr = data->channel_data[chan].data_rate;
+	mask = ADS1015_CFG_MUX_MASK | ADS1015_CFG_PGA_MASK |
+		ADS1015_CFG_DR_MASK;
+	cfg = chan << ADS1015_CFG_MUX_SHIFT | pga << ADS1015_CFG_PGA_SHIFT |
+		dr << ADS1015_CFG_DR_SHIFT;
 
-	ret = regmap_update_bits_check(data->regmap, ADS1015_CFG_REG,
-				       ADS1015_CFG_MUX_MASK |
-				       ADS1015_CFG_PGA_MASK |
-				       ADS1015_CFG_DR_MASK,
-				       chan << ADS1015_CFG_MUX_SHIFT |
-				       pga << ADS1015_CFG_PGA_SHIFT |
-				       dr << ADS1015_CFG_DR_SHIFT,
-				       &change);
-	if (ret < 0)
+	cfg = (old & ~mask) | (cfg & mask);
+
+	ret = regmap_write(data->regmap, ADS1015_CFG_REG, cfg);
+	if (ret)
 		return ret;
 
-	if (change || data->conv_invalid) {
-		conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
+	if (old != cfg || data->conv_invalid) {
+		int dr_old = (old & ADS1015_CFG_DR_MASK) >>
+				ADS1015_CFG_DR_SHIFT;
+
+		conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr_old]);
+		conv_time += DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
 		usleep_range(conv_time, conv_time + 1);
 		data->conv_invalid = false;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/iio-adc-ti-ads1015-enable-conversion-when-config_pm-is-not-set.patch queue-4.9/iio-adc-ti-ads1015-add-adequate-wait-time-to-get-correct-conversion.patch queue-4.9/iio-adc-ti-ads1015-don-t-return-invalid-value-from-buffer-setup-callbacks.patch queue-4.9/iio-adc-ti-ads1015-fix-incorrect-data-rate-setting-update.patch queue-4.9/iio-adc-ti-ads1015-fix-scale-information-for-ads1115.patch queue-4.9/iio-adc-ti-ads1015-avoid-getting-stale-result-after-runtime-resume.patch