[4.2.y-ckt stable] Patch "hwmon: (ads7828) Enable internal reference" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    hwmon: (ads7828) Enable internal reference

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From cee60c5f36c92cc06177ffff186f2695d595896b Mon Sep 17 00:00:00 2001
From: Akshay Bhat <akshay.bhat at timesys.com>
Date: Mon, 18 Apr 2016 15:47:53 -0400
Subject: hwmon: (ads7828) Enable internal reference

commit 7a18afe8097731b8ffb6cb5b2b3b418ded77c105 upstream.

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 at timesys.com>
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/hwmon/ads7828.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hwmon/ads7828.c b/drivers/hwmon/ads7828.c
index 6c99ee7..ee396ff 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 voltage 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);
--
2.7.4