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[PATCH 4.9 13/32] iio: adc: ti-ads1015: add adequate wait time to get correct conversion

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

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

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

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.

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 |   31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

--- a/drivers/iio/adc/ti-ads1015.c
+++ b/drivers/iio/adc/ti-ads1015.c
@@ -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;
 	}

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[PATCH 4.9 00/32] 4.9.49-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 12/32] iio: adc: ti-ads1015: dont return invalid value from buffer setup callbacks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 28/32] cs5536: add support for IDE controller variant Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 03/32] usb: Add device quirk for Logitech HD Pro Webcam C920-C Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 25/32] s390/mm: avoid empty zero pages for KVM guests to avoid postcopy hangs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 04/32] usb:xhci:Fix regression when ATI chipsets detected Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 18/32] Input: trackpoint - assume 3 buttons when buttons detection fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 09/32] iio: adc: ti-ads1015: fix scale information for ADS1115 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 30/32] scsi: sg: recheck MMAP_IO request length with lock held Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 16/32] intel_th: pci: Add Cannon Lake PCH-LP support Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 26/32] drm/nouveau/pci/msi: disable MSI on big-endian platforms by default Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 07/32] staging/rts5208: fix incorrect shift to extract upper nybble Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 27/32] workqueue: Fix flag collision Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 29/32] scsi: sg: protect against races between mmap() and SG_SET_RESERVED_SIZE Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:30 +0200
  [PATCH 4.9 20/32] Bluetooth: Add support of 13d3:3494 RTL8723BE device Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 17/32] ath10k: fix memory leak in rx ring buffer allocation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 14/32] driver core: bus: Fix a potential double free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 11/32] iio: adc: ti-ads1015: avoid getting stale result after runtime resume Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 15/32] intel_th: pci: Add Cannon Lake PCH-H support Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 13/32] iio: adc: ti-ads1015: add adequate wait time to get correct conversion Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 21/32] iwlwifi: pci: add new PCI ID for 7265D Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 10/32] iio: adc: ti-ads1015: enable conversion when CONFIG_PM is not set Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 19/32] rtlwifi: rtl_pci_probe: Fix fail path of _rtl_pci_find_adapter Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  [PATCH 4.9 01/32] usb: quirks: add delay init quirk for Corsair Strafe RGB keyboard Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-08 15:40 +0200
  Re: [PATCH 4.9 00/32] 4.9.49-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-09-08 20:40 +0200
  Re: [PATCH 4.9 00/32] 4.9.49-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-09 15:50 +0200

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