[PATCH 3/4] hwmon: Add a simple driver to read the MXS SoC temperature

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

The low resolution ADC of the mxs is able to read an internal temperature
sensor, expose that using hwmon.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 .../devicetree/bindings/hwmon/mxs-cputemp.txt      |  18 +++
 Documentation/hwmon/mxs-cputemp                    |  29 +++++
 drivers/hwmon/Kconfig                              |  10 ++
 drivers/hwmon/Makefile                             |   1 +
 drivers/hwmon/mxs-cputemp.c                        | 132 +++++++++++++++++++++
 5 files changed, 190 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/mxs-cputemp.txt
 create mode 100644 Documentation/hwmon/mxs-cputemp
 create mode 100644 drivers/hwmon/mxs-cputemp.c

diff --git a/Documentation/devicetree/bindings/hwmon/mxs-cputemp.txt b/Documentation/devicetree/bindings/hwmon/mxs-cputemp.txt
new file mode 100644
index 0000000..7d3ae47
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/mxs-cputemp.txt
@@ -0,0 +1,18 @@
+mxs cputemp hwmon sensors
+-------------------------
+
+See: Documentation/hwmon/mxs-cputemp
+
+Required properties:
+- compatible: should be "fsl,mxs-internal-temp"
+- io-channels: should list the two adc channels needed to calculate the
+	       temperature
+- io-channel-names: should map the previously listed adc channels to the "min"
+		    and "max" value
+
+Example:
+	temp {
+		compatible = "fsl,mxs-internal-temp";
+		io-channels = <&lradc 8>, <&lradc 9>;
+		io-channel-names = "min", "max";
+	};
diff --git a/Documentation/hwmon/mxs-cputemp b/Documentation/hwmon/mxs-cputemp
new file mode 100644
index 0000000..6c6201f
--- /dev/null
+++ b/Documentation/hwmon/mxs-cputemp
@@ -0,0 +1,29 @@
+Kernel driver mxs-cputemp
+=========================
+
+Supported chips:
+  * Freescale i.mx28
+    Datasheet: i.MX28 Applications Processor Reference Manual, Rev. 1, 2010
+    	       http://cache.freescale.com/files/dsp/doc/ref_manual/MCIMX28RM.pdf
+
+Author: Alexandre Belloni
+
+Description
+-----------
+This driver permits reading the internal die temperature sensor embedded inside
+Freescale i.mx28 SoCs. This sensor is read through two channels of the on chip
+Low-Resolution ADC. After calculation, the three-sigma error of the temperature
+sensor should be within ± 1.5% in degrees Kelvin. Additionally, the temperature
+sampling has a three-sigma sample-to-sample variation of 2 degrees Kelvin. If
+desired, this error can be removed by oversampling and averaging the temperature
+result.
+
+The formula is:
+	(Channel9 – Channel8) * Gain_correction/4
+
+As recommended by the datasheet, Gain_correction is equal to 1.012.
+
+sysfs entries
+-------------
+temp1_input	Measured and corrected temperature in millidegrees Celsius
+
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 0428e8a..2daf794 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -929,6 +929,16 @@ config SENSORS_MCP3021
 	  This driver can also be built as a module.  If so, the module
 	  will be called mcp3021.
 
+config SENSORS_MXS_CPU
+	tristate "MXS internal CPU temperature sensor"
+	depends on MXS_LRADC
+	help
+	  If you say yes here you get support for the i.mx28 internal
+	  temperature sensor.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called mxs-cputemp
+
 config SENSORS_NCT6775
 	tristate "Nuvoton NCT6775F and compatibles"
 	depends on !PPC
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index d17d3e6..366c92d 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -108,6 +108,7 @@ obj-$(CONFIG_SENSORS_MAX6650)	+= max6650.o
 obj-$(CONFIG_SENSORS_MAX6697)	+= max6697.o
 obj-$(CONFIG_SENSORS_MC13783_ADC)+= mc13783-adc.o
 obj-$(CONFIG_SENSORS_MCP3021)	+= mcp3021.o
+obj-$(CONFIG_SENSORS_MXS_CPU)	+= mxs-cputemp.o
 obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
 obj-$(CONFIG_SENSORS_NTC_THERMISTOR)	+= ntc_thermistor.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
diff --git a/drivers/hwmon/mxs-cputemp.c b/drivers/hwmon/mxs-cputemp.c
new file mode 100644
index 0000000..a312fb5
--- /dev/null
+++ b/drivers/hwmon/mxs-cputemp.c
@@ -0,0 +1,132 @@
+/*
+ * Driver for the mxs internal temperature sensor
+ *
+ * Copyright 2013 Free Electrons
+ *
+ * Licensed under the GPLv2 or later.
+ */
+
+#define DRVNAME "mxs-hwmon"
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/iio/consumer.h>
+
+#define GAIN_CORRECTION 1012
+
+/* The value we calculate from the ADCs is in Kelvins, don't forget to convert
+ * it to Celsius */
+#define VALUES_TO_MILLIC(min, max) ((max - min) * GAIN_CORRECTION / 4 - 272150)
+
+struct mxs_hwmon_data {
+	struct device *hwmon_dev;
+	struct iio_channel *chan_min;
+	struct iio_channel *chan_max;
+};
+
+static int mxs_hwmon_show_temp(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	int err, val_min, val_max;
+
+	struct mxs_hwmon_data *data = dev_get_drvdata(dev);
+
+	err = iio_read_channel_raw(data->chan_min, &val_min);
+	if (err < 0)
+		return err;
+
+	err = iio_read_channel_raw(data->chan_max, &val_max);
+	if (err < 0)
+		return err;
+
+	return sprintf(buf, "%u\n", VALUES_TO_MILLIC(val_min, val_max));
+}
+
+static DEVICE_ATTR(temp1_input, S_IRUGO, mxs_hwmon_show_temp, NULL);
+
+static int mxs_hwmon_probe(struct platform_device *pdev)
+{
+	int err;
+	struct mxs_hwmon_data *data;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, data);
+
+	err = device_create_file(&pdev->dev, &dev_attr_temp1_input);
+	if (err)
+		return err;
+
+	data->chan_min = iio_channel_get(&pdev->dev, "min");
+	if (IS_ERR(data->chan_min)) {
+		err = PTR_ERR(data->chan_min);
+		goto error_chan_min;
+	}
+
+	data->chan_max = iio_channel_get(&pdev->dev, "max");
+	if (IS_ERR(data->chan_max)) {
+		err = PTR_ERR(data->chan_max);
+		goto error_chan_max;
+	}
+
+	data->hwmon_dev = hwmon_device_register(&pdev->dev);
+	if (IS_ERR(data->hwmon_dev)) {
+		err = PTR_ERR(data->hwmon_dev);
+		goto error_hwmon;
+	}
+
+	return 0;
+
+error_hwmon:
+	iio_channel_release(data->chan_max);
+error_chan_max:
+	iio_channel_release(data->chan_min);
+error_chan_min:
+	device_remove_file(&pdev->dev, &dev_attr_temp1_input);
+
+	return err;
+}
+
+static int mxs_hwmon_remove(struct platform_device *pdev)
+{
+	struct mxs_hwmon_data *data = platform_get_drvdata(pdev);
+
+	iio_channel_release(data->chan_min);
+	iio_channel_release(data->chan_max);
+	hwmon_device_unregister(data->hwmon_dev);
+
+	device_remove_file(&pdev->dev, &dev_attr_temp1_input);
+
+	return 0;
+}
+
+static struct of_device_id mxs_hwmon_of_match[] = {
+	{ .compatible = "fsl,mxs-internal-temp", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, mxs_hwmon_of_match);
+
+static struct platform_driver mxs_hwmon_driver = {
+	.probe = mxs_hwmon_probe,
+	.remove = mxs_hwmon_remove,
+	.driver	= {
+		.name = DRVNAME,
+		.owner = THIS_MODULE,
+		.of_match_table = mxs_hwmon_of_match,
+	},
+};
+
+module_platform_driver(mxs_hwmon_driver);
+
+MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@free-electrons.com>");
+MODULE_DESCRIPTION("Freescale i.MX28 hwmon sensor driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:mxs-hwmon");
-- 
1.8.1.2