[PATCH V3 1/2] thermal: generic-adc: Add DT binding for ADC based thermal sensor

[PATCH V3 1/2] thermal: generic-adc: Add DT binding for ADC based thermal sensor

[Laxman Dewangan]

Sometimes, thermal sensors like NCT thermistors are connected to
the ADC channel. The temperature is read by reading the voltage
across the sensor resistance via ADC and referring the lookup
table for ADC value to temperature.

Add DT binding doc for the ADC based thermal sensor driver to
detail the DT property and provide the example for how to use it.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>

---
Changes from V1:
- Make the lookup table to two dimensional instead of single array of linear
  step of temperature.
- Remove detailing of IIO frameowrk and drivers.
- Added proper braces, indenting and labels.

Changes from V2:
- Handle comment from Rob for detailing the first and second value of the array
  and remove @ in the node name.

 .../bindings/thermal/thermal-generic-adc.txt       | 89 ++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt

diff --git a/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt b/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt
new file mode 100644
index 0000000..d7235550
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt
@@ -0,0 +1,89 @@
+General Purpose Analog To Digital Converter (ADC) based thermal sensor.
+
+On some of platforms, thermal sensor like thermistors are connected to
+one of ADC channel and sensor resistance is read via voltage across the
+sensor resistor. The voltage read across the sensor is mapped to
+temperature using voltage-temperature lookup table.
+
+Required properties:
+===================
+- compatible:		     Must be "generic-adc-thermal".
+- temperature-lookup-table:  Two dimensional array of Integer; lookup table
+			     to map the relation between ADC value and
+			     temperature. When ADC is read, the value is
+			     looked up on the table to get the equivalent
+			     temperature.
+			     The first value of the each row of array is the
+			     temperature in milliCelsius and second value of
+			     the each row of array is the ADC read value.
+- #thermal-sensor-cells:     Should be 1. See ./thermal.txt for a description
+			     of this property.
+
+Example :
+#include <dt-bindings/thermal/thermal.h>
+
+i2c@7000c400 {
+	ads1015: ads1015@4a {
+		reg = <0x4a>;
+		compatible = "ads1015";
+		sampling-frequency = <3300>;
+		#io-channel-cells = <1>;
+	};
+};
+
+tboard_thermistor: thermal-sensor {
+	compatible = "generic-adc-thermal";
+	#thermal-sensor-cells = <0>;
+	io-channels = <&ads1015 1>;
+	io-channel-names = "sensor-channel";
+	temperature-lookup-table = <    (-40000) 2578
+					(-39000) 2577
+					(-38000) 2576
+					(-37000) 2575
+					(-36000) 2574
+					(-35000) 2573
+					(-34000) 2572
+					(-33000) 2571
+					(-32000) 2569
+					(-31000) 2568
+					(-30000) 2567
+					::::::::::
+					118000 254
+					119000 247
+					120000 240
+					121000 233
+					122000 226
+					123000 220
+					124000 214
+					125000 208>;
+};
+
+dummy_cool_dev: dummy-cool-dev {
+	compatible = "dummy-cooling-dev";
+	#cooling-cells = <2>; /* min followed by max */
+};
+
+thermal-zones {
+	Tboard {
+		polling-delay = <15000>; /* milliseconds */
+		polling-delay-passive = <0>; /* milliseconds */
+		thermal-sensors = <&tboard_thermistor>;
+
+		trips {
+			therm_est_trip: therm_est_trip {
+				temperature = <40000>;
+				type = "active";
+				hysteresis = <1000>;
+			};
+		};
+
+		cooling-maps {
+			map0 {
+				trip = <&therm_est_trip>;
+				cooling-device = <&dummy_cool_dev THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
+				contribution = <100>;
+			};
+
+		};
+	};
+};
-- 
2.1.4

[PATCH V3 2/2] thermal: generic-adc: Add ADC based thermal sensor driver

[Laxman Dewangan]

In some of platform, thermal sensors like NCT thermistors are
connected to the one of ADC channel. The temperature is read by
reading the voltage across the sensor resistance via ADC. Lookup
table for ADC read value to temperature is referred to get
temperature. ADC is read via IIO framework.

Add support for thermal sensor driver which read the voltage across
sensor resistance from ADC through IIO framework.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>

---
Changes from V1:
- Use the two dimensional lookup table for temperature vs ADC value.
- Use non devm_ for thermal zone sensor registration as there may be
  race between IIO channel release and temperature read.

Changes from V2:
- None.

 drivers/thermal/Kconfig               |  10 ++
 drivers/thermal/Makefile              |   1 +
 drivers/thermal/thermal-generic-adc.c | 195 ++++++++++++++++++++++++++++++++++
 3 files changed, 206 insertions(+)
 create mode 100644 drivers/thermal/thermal-generic-adc.c

diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 594748e..d7d0136 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -400,4 +400,14 @@ config QCOM_SPMI_TEMP_ALARM
 	  real time die temperature if an ADC is present or an estimate of the
 	  temperature based upon the over temperature stage value.
 
+config GENERIC_ADC_THERMAL
+	tristate "Generic ADC based thermal sensor"
+	depends on IIO
+	help
+	  This enabled a thermal sysfs driver for the temperature sensor
+	  which is connected to the General Purpose ADC. The ADC channel
+	  is read via IIO framework and the channel information is provided
+	  to this driver. This driver reports the temperature by reading ADC
+	  channel and converts it to temperature based on lookup table.
+
 endif
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index d64f7f7..904593a 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -49,3 +49,4 @@ obj-$(CONFIG_ST_THERMAL)	+= st/
 obj-$(CONFIG_TEGRA_SOCTHERM)	+= tegra/
 obj-$(CONFIG_HISI_THERMAL)     += hisi_thermal.o
 obj-$(CONFIG_MTK_THERMAL)	+= mtk_thermal.o
+obj-$(CONFIG_GENERIC_ADC_THERMAL)	+= thermal-generic-adc.o
diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
new file mode 100644
index 0000000..902cf12
--- /dev/null
+++ b/drivers/thermal/thermal-generic-adc.c
@@ -0,0 +1,195 @@
+/*
+ * Generic ADC thermal driver
+ *
+ * Copyright (C) 2016 NVIDIA CORPORATION. All rights reserved.
+ *
+ * Author: Laxman Dewangan <ldewangan@nvidia.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/iio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/thermal.h>
+
+struct gadc_thermal_info {
+	struct device *dev;
+	struct thermal_zone_device *tz_dev;
+	struct iio_channel *channel;
+	s32 *lookup_table;
+	int nlookup_table;
+};
+
+static int gadc_thermal_read_channel(struct gadc_thermal_info *gti, int *val)
+{
+	int ret;
+
+	ret = iio_read_channel_processed(gti->channel, val);
+	if (ret < 0)
+		ret = iio_read_channel_raw(gti->channel, val);
+	if (ret < 0)
+		return ret;
+
+	return ret;
+}
+
+static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
+{
+	int temp, adc_hi, adc_lo;
+	int i;
+
+	for (i = 0; i < gti->nlookup_table; i++) {
+		if (val >= gti->lookup_table[2 * i + 1])
+			break;
+	}
+
+	if (i == 0) {
+		temp = gti->lookup_table[0];
+	} else if (i >= (gti->nlookup_table - 1)) {
+		temp = gti->lookup_table[2 * (gti->nlookup_table - 1)];
+	} else {
+		adc_hi = gti->lookup_table[2 * i - 1];
+		adc_lo = gti->lookup_table[2 * i + 1];
+		temp = gti->lookup_table[2 * i];
+		temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
+	}
+
+	return temp;
+}
+
+static int gadc_thermal_get_temp(void *data, int *temp)
+{
+	struct gadc_thermal_info *gti = data;
+	int val;
+	int ret;
+
+	ret = gadc_thermal_read_channel(gti, &val);
+	if (ret < 0) {
+		dev_err(gti->dev, "IIO channel read failed %d\n", ret);
+		return ret;
+	}
+	*temp = gadc_thermal_adc_to_temp(gti, val);
+
+	return 0;
+}
+
+static const struct thermal_zone_of_device_ops gadc_thermal_ops = {
+	.get_temp = gadc_thermal_get_temp,
+};
+
+static int gadc_thermal_read_linear_lookup_table(struct device *dev,
+						 struct gadc_thermal_info *gti)
+{
+	struct device_node *np = dev->of_node;
+	int ntable;
+	int ret;
+
+	ntable = of_property_count_elems_of_size(np, "temperature-lookup-table",
+						 sizeof(u32));
+	if (ntable < 0) {
+		dev_err(dev, "Lookup table is not provided\n");
+		return ntable;
+	}
+
+	if (ntable % 2) {
+		dev_err(dev, "Pair of temperature vs ADC read value missing\n");
+		return -EINVAL;
+	}
+
+	gti->lookup_table = devm_kzalloc(dev, sizeof(*gti->lookup_table) *
+					 ntable, GFP_KERNEL);
+	if (!gti->lookup_table)
+		return -ENOMEM;
+
+	ret = of_property_read_u32_array(np, "temperature-lookup-table",
+					 (u32 *)gti->lookup_table, ntable);
+	if (ret < 0) {
+		dev_err(dev, "Failed to read temperature lookup table: %d\n",
+			ret);
+		return ret;
+	}
+
+	gti->nlookup_table = ntable / 2;
+
+	return 0;
+}
+
+static int gadc_thermal_probe(struct platform_device *pdev)
+{
+	struct gadc_thermal_info *gti;
+	int ret;
+
+	if (!pdev->dev.of_node) {
+		dev_err(&pdev->dev, "Only DT based supported\n");
+		return -ENODEV;
+	}
+
+	gti = devm_kzalloc(&pdev->dev, sizeof(*gti), GFP_KERNEL);
+	if (!gti)
+		return -ENOMEM;
+
+	ret = gadc_thermal_read_linear_lookup_table(&pdev->dev, gti);
+	if (ret < 0)
+		return ret;
+
+	gti->dev = &pdev->dev;
+	platform_set_drvdata(pdev, gti);
+
+	gti->channel = iio_channel_get(&pdev->dev, "sensor-channel");
+	if (IS_ERR(gti->channel)) {
+		ret = PTR_ERR(gti->channel);
+		dev_err(&pdev->dev, "IIO channel not found: %d\n", ret);
+		return ret;
+	}
+
+	gti->tz_dev = thermal_zone_of_sensor_register(&pdev->dev, 0,
+						      gti, &gadc_thermal_ops);
+	if (IS_ERR(gti->tz_dev)) {
+		ret = PTR_ERR(gti->tz_dev);
+		dev_err(&pdev->dev, "Thermal zone sensor register failed: %d\n",
+			ret);
+		goto sensor_fail;
+	}
+
+	return 0;
+
+sensor_fail:
+	iio_channel_release(gti->channel);
+
+	return ret;
+}
+
+static int gadc_thermal_remove(struct platform_device *pdev)
+{
+	struct gadc_thermal_info *gti = platform_get_drvdata(pdev);
+
+	thermal_zone_of_sensor_unregister(&pdev->dev, gti->tz_dev);
+	iio_channel_release(gti->channel);
+
+	return 0;
+}
+
+static const struct of_device_id of_adc_thermal_match[] = {
+	{ .compatible = "generic-adc-thermal", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, of_adc_thermal_match);
+
+static struct platform_driver gadc_thermal_driver = {
+	.driver = {
+		.name = "generic-adc-thermal",
+		.of_match_table = of_adc_thermal_match,
+	},
+	.probe = gadc_thermal_probe,
+	.remove = gadc_thermal_remove,
+};
+
+module_platform_driver(gadc_thermal_driver);
+
+MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
+MODULE_DESCRIPTION("Generic ADC thermal driver using IIO framework with DT");
+MODULE_LICENSE("GPL v2");
-- 
2.1.4

Re: [PATCH V3 1/2] thermal: generic-adc: Add DT binding for ADC based thermal sensor

[Rob Herring]

On Thu, Apr 14, 2016 at 08:11:17PM +0530, Laxman Dewangan wrote:
> Sometimes, thermal sensors like NCT thermistors are connected to
> the ADC channel. The temperature is read by reading the voltage
> across the sensor resistance via ADC and referring the lookup
> table for ADC value to temperature.
> 
> Add DT binding doc for the ADC based thermal sensor driver to
> detail the DT property and provide the example for how to use it.
> 
> Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
> 
> ---
> Changes from V1:
> - Make the lookup table to two dimensional instead of single array of linear
>   step of temperature.
> - Remove detailing of IIO frameowrk and drivers.
> - Added proper braces, indenting and labels.
> 
> Changes from V2:
> - Handle comment from Rob for detailing the first and second value of the array
>   and remove @ in the node name.
> 
>  .../bindings/thermal/thermal-generic-adc.txt       | 89 ++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt

Acked-by: Rob Herring <rob@kernel.org>

Re: [PATCH V3 2/2] thermal: generic-adc: Add ADC based thermal sensor driver

[Jonathan Cameron]

On 14/04/16 15:41, Laxman Dewangan wrote:
> In some of platform, thermal sensors like NCT thermistors are
> connected to the one of ADC channel. The temperature is read by
> reading the voltage across the sensor resistance via ADC. Lookup
> table for ADC read value to temperature is referred to get
> temperature. ADC is read via IIO framework.
> 
> Add support for thermal sensor driver which read the voltage across
> sensor resistance from ADC through IIO framework.
> 
> Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
One question inline on whether it makes sense to fall back to a
raw IIO value read if the processed one isn't available.  Looks to me
like a solution that will fail if anyone 'fixes' the underlying ADC driver
as then the tables will suddenly be wrong.

Jonathan
> 
> ---
> Changes from V1:
> - Use the two dimensional lookup table for temperature vs ADC value.
> - Use non devm_ for thermal zone sensor registration as there may be
>   race between IIO channel release and temperature read.
> 
> Changes from V2:
> - None.
> 
>  drivers/thermal/Kconfig               |  10 ++
>  drivers/thermal/Makefile              |   1 +
>  drivers/thermal/thermal-generic-adc.c | 195 ++++++++++++++++++++++++++++++++++
>  3 files changed, 206 insertions(+)
>  create mode 100644 drivers/thermal/thermal-generic-adc.c
> 
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 594748e..d7d0136 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -400,4 +400,14 @@ config QCOM_SPMI_TEMP_ALARM
>  	  real time die temperature if an ADC is present or an estimate of the
>  	  temperature based upon the over temperature stage value.
>  
> +config GENERIC_ADC_THERMAL
> +	tristate "Generic ADC based thermal sensor"
> +	depends on IIO
> +	help
> +	  This enabled a thermal sysfs driver for the temperature sensor
> +	  which is connected to the General Purpose ADC. The ADC channel
> +	  is read via IIO framework and the channel information is provided
> +	  to this driver. This driver reports the temperature by reading ADC
> +	  channel and converts it to temperature based on lookup table.
> +
>  endif
> diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> index d64f7f7..904593a 100644
> --- a/drivers/thermal/Makefile
> +++ b/drivers/thermal/Makefile
> @@ -49,3 +49,4 @@ obj-$(CONFIG_ST_THERMAL)	+= st/
>  obj-$(CONFIG_TEGRA_SOCTHERM)	+= tegra/
>  obj-$(CONFIG_HISI_THERMAL)     += hisi_thermal.o
>  obj-$(CONFIG_MTK_THERMAL)	+= mtk_thermal.o
> +obj-$(CONFIG_GENERIC_ADC_THERMAL)	+= thermal-generic-adc.o
> diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
> new file mode 100644
> index 0000000..902cf12
> --- /dev/null
> +++ b/drivers/thermal/thermal-generic-adc.c
> @@ -0,0 +1,195 @@
> +/*
> + * Generic ADC thermal driver
> + *
> + * Copyright (C) 2016 NVIDIA CORPORATION. All rights reserved.
> + *
> + * Author: Laxman Dewangan <ldewangan@nvidia.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#include <linux/iio/consumer.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/thermal.h>
> +
> +struct gadc_thermal_info {
> +	struct device *dev;
> +	struct thermal_zone_device *tz_dev;
> +	struct iio_channel *channel;
> +	s32 *lookup_table;
> +	int nlookup_table;
> +};
> +
> +static int gadc_thermal_read_channel(struct gadc_thermal_info *gti, int *val)
> +{
> +	int ret;
> +
> +	ret = iio_read_channel_processed(gti->channel, val);
> +	if (ret < 0)
> +		ret = iio_read_channel_raw(gti->channel, val);
Is this case actually useful given it means the scaling of the adc
isn't known?

I suppose you might have defined the table in terms of raw readings,
but then when someone comes along and 'fixes' the ADC driver to output
it's scale your table will be wrong.


> +	if (ret < 0)
> +		return ret;
> +
> +	return ret;
> +}
> +
> +static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
> +{
> +	int temp, adc_hi, adc_lo;
> +	int i;
> +
> +	for (i = 0; i < gti->nlookup_table; i++) {
> +		if (val >= gti->lookup_table[2 * i + 1])
> +			break;
> +	}
> +
> +	if (i == 0) {
> +		temp = gti->lookup_table[0];
> +	} else if (i >= (gti->nlookup_table - 1)) {
> +		temp = gti->lookup_table[2 * (gti->nlookup_table - 1)];
> +	} else {
> +		adc_hi = gti->lookup_table[2 * i - 1];
> +		adc_lo = gti->lookup_table[2 * i + 1];
> +		temp = gti->lookup_table[2 * i];
> +		temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
> +	}
> +
> +	return temp;
> +}
> +
> +static int gadc_thermal_get_temp(void *data, int *temp)
> +{
> +	struct gadc_thermal_info *gti = data;
> +	int val;
> +	int ret;
> +
> +	ret = gadc_thermal_read_channel(gti, &val);
> +	if (ret < 0) {
> +		dev_err(gti->dev, "IIO channel read failed %d\n", ret);
> +		return ret;
> +	}
> +	*temp = gadc_thermal_adc_to_temp(gti, val);
> +
> +	return 0;
> +}
> +
> +static const struct thermal_zone_of_device_ops gadc_thermal_ops = {
> +	.get_temp = gadc_thermal_get_temp,
> +};
> +
> +static int gadc_thermal_read_linear_lookup_table(struct device *dev,
> +						 struct gadc_thermal_info *gti)
> +{
> +	struct device_node *np = dev->of_node;
> +	int ntable;
> +	int ret;
> +
> +	ntable = of_property_count_elems_of_size(np, "temperature-lookup-table",
> +						 sizeof(u32));
> +	if (ntable < 0) {
> +		dev_err(dev, "Lookup table is not provided\n");
> +		return ntable;
> +	}
> +
> +	if (ntable % 2) {
> +		dev_err(dev, "Pair of temperature vs ADC read value missing\n");
> +		return -EINVAL;
> +	}
> +
> +	gti->lookup_table = devm_kzalloc(dev, sizeof(*gti->lookup_table) *
> +					 ntable, GFP_KERNEL);
> +	if (!gti->lookup_table)
> +		return -ENOMEM;
> +
> +	ret = of_property_read_u32_array(np, "temperature-lookup-table",
> +					 (u32 *)gti->lookup_table, ntable);
> +	if (ret < 0) {
> +		dev_err(dev, "Failed to read temperature lookup table: %d\n",
> +			ret);
> +		return ret;
> +	}
> +
> +	gti->nlookup_table = ntable / 2;
> +
> +	return 0;
> +}
> +
> +static int gadc_thermal_probe(struct platform_device *pdev)
> +{
> +	struct gadc_thermal_info *gti;
> +	int ret;
> +
> +	if (!pdev->dev.of_node) {
> +		dev_err(&pdev->dev, "Only DT based supported\n");
> +		return -ENODEV;
> +	}
> +
> +	gti = devm_kzalloc(&pdev->dev, sizeof(*gti), GFP_KERNEL);
> +	if (!gti)
> +		return -ENOMEM;
> +
> +	ret = gadc_thermal_read_linear_lookup_table(&pdev->dev, gti);
> +	if (ret < 0)
> +		return ret;
> +
> +	gti->dev = &pdev->dev;
> +	platform_set_drvdata(pdev, gti);
> +
> +	gti->channel = iio_channel_get(&pdev->dev, "sensor-channel");
> +	if (IS_ERR(gti->channel)) {
> +		ret = PTR_ERR(gti->channel);
> +		dev_err(&pdev->dev, "IIO channel not found: %d\n", ret);
> +		return ret;
> +	}
> +
> +	gti->tz_dev = thermal_zone_of_sensor_register(&pdev->dev, 0,
> +						      gti, &gadc_thermal_ops);
> +	if (IS_ERR(gti->tz_dev)) {
> +		ret = PTR_ERR(gti->tz_dev);
> +		dev_err(&pdev->dev, "Thermal zone sensor register failed: %d\n",
> +			ret);
> +		goto sensor_fail;
> +	}
> +
> +	return 0;
> +
> +sensor_fail:
> +	iio_channel_release(gti->channel);
> +
> +	return ret;
> +}
> +
> +static int gadc_thermal_remove(struct platform_device *pdev)
> +{
> +	struct gadc_thermal_info *gti = platform_get_drvdata(pdev);
> +
> +	thermal_zone_of_sensor_unregister(&pdev->dev, gti->tz_dev);
> +	iio_channel_release(gti->channel);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id of_adc_thermal_match[] = {
> +	{ .compatible = "generic-adc-thermal", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, of_adc_thermal_match);
> +
> +static struct platform_driver gadc_thermal_driver = {
> +	.driver = {
> +		.name = "generic-adc-thermal",
> +		.of_match_table = of_adc_thermal_match,
> +	},
> +	.probe = gadc_thermal_probe,
> +	.remove = gadc_thermal_remove,
> +};
> +
> +module_platform_driver(gadc_thermal_driver);
> +
> +MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
> +MODULE_DESCRIPTION("Generic ADC thermal driver using IIO framework with DT");
> +MODULE_LICENSE("GPL v2");
> 

Re: [PATCH V3 2/2] thermal: generic-adc: Add ADC based thermal sensor driver

[Laxman Dewangan]

On Sunday 17 April 2016 04:24 PM, Jonathan Cameron wrote:
> On 14/04/16 15:41, Laxman Dewangan wrote:
> +static int gadc_thermal_read_channel(struct gadc_thermal_info *gti, int *val)
> +{
> +	int ret;
> +
> +	ret = iio_read_channel_processed(gti->channel, val);
> +	if (ret < 0)
> +		ret = iio_read_channel_raw(gti->channel, val);
> Is this case actually useful given it means the scaling of the adc
> isn't known?
>
> I suppose you might have defined the table in terms of raw readings,
> but then when someone comes along and 'fixes' the ADC driver to output
> it's scale your table will be wrong.
>

Yes, that may be possible if someone just move the implementation of 
processed read to raw read.
I assumed that some of adc driver implemented as raw and some of 
implemented as processed and so fallback.

However, if adc driver has processed implementation then it should not 
move to raw and deprecate the processed.

It seems raw as default should be better option. We can have two option now:

- Support raw only, not to processed.

- Or support the raw as default and processed as the optional from DT.
if (!processed)
     read_raw()
else
   read_processed()


Your opinion?

Re: [PATCH V3 2/2] thermal: generic-adc: Add ADC based thermal sensor driver

[Jonathan Cameron]

On 18 April 2016 17:49:39 BST, Laxman Dewangan <ldewangan@nvidia.com> wrote:
>
>On Sunday 17 April 2016 04:24 PM, Jonathan Cameron wrote:
>> On 14/04/16 15:41, Laxman Dewangan wrote:
>> +static int gadc_thermal_read_channel(struct gadc_thermal_info *gti,
>int *val)
>> +{
>> +	int ret;
>> +
>> +	ret = iio_read_channel_processed(gti->channel, val);
>> +	if (ret < 0)
>> +		ret = iio_read_channel_raw(gti->channel, val);
>> Is this case actually useful given it means the scaling of the adc
>> isn't known?
>>
>> I suppose you might have defined the table in terms of raw readings,
>> but then when someone comes along and 'fixes' the ADC driver to
>output
>> it's scale your table will be wrong.
>>
>
>Yes, that may be possible if someone just move the implementation of 
>processed read to raw read.
>I assumed that some of adc driver implemented as raw and some of 
>implemented as processed and so fallback.
>
>However, if adc driver has processed implementation then it should not 
>move to raw and deprecate the processed.
>
>It seems raw as default should be better option. We can have two option
>now:
>
>- Support raw only, not to processed.
>
>- Or support the raw as default and processed as the optional from DT.
>if (!processed)
>     read_raw()
>else
>   read_processed()
>
>
>Your opinion?
Processed only. It will compute the right value if raw and scale are provided by the
 device (which they should be for an ADC). The read_processed function does
 the maths if needed.

 The only time devices should
 supply raw without scale is if their is no direct transform ( e.g. an infrared
 intensity measure where only known transform involves combining it with
 another signal) or their is an external unknown (e.g. proximity sensors where
 you have to know what they were close to in order to know the scaling!)

If there is a conventional ADC driver not providing either processed directly or
 both raw and scale let us know and we will fix it!

Jonathan
>
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-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH V3 2/2] thermal: generic-adc: Add ADC based thermal sensor driver

[Laxman Dewangan]

On Monday 18 April 2016 11:01 PM, Jonathan Cameron wrote:
>
> On 18 April 2016 17:49:39 BST, Laxman Dewangan <ldewangan@nvidia.com> wrote:
>> On Sunday 17 April 2016 04:24 PM, Jonathan Cameron wrote:
>>> On 14/04/16 15:41, Laxman Dewangan wrote:
>>> +static int gadc_thermal_read_channel(struct gadc_thermal_info *gti,
>> int *val)
>>> +{
>>> +	int ret;
>>> +
>>> +	ret = iio_read_channel_processed(gti->channel, val);
>>> +	if (ret < 0)
>>> +		ret = iio_read_channel_raw(gti->channel, val);
>>> Is this case actually useful given it means the scaling of the adc
>>> isn't known?
>>>
>>> I suppose you might have defined the table in terms of raw readings,
>>> but then when someone comes along and 'fixes' the ADC driver to
>> output
>>> it's scale your table will be wrong.
>>>
>> Yes, that may be possible if someone just move the implementation of
>> processed read to raw read.
>> I assumed that some of adc driver implemented as raw and some of
>> implemented as processed and so fallback.
>>
>> However, if adc driver has processed implementation then it should not
>> move to raw and deprecate the processed.
>>
>> It seems raw as default should be better option. We can have two option
>> now:
>>
>> - Support raw only, not to processed.
>>
>> - Or support the raw as default and processed as the optional from DT.
>> if (!processed)
>>      read_raw()
>> else
>>    read_processed()
>>
>>
>> Your opinion?
> Processed only. It will compute the right value if raw and scale are provided by the
>   device (which they should be for an ADC). The read_processed function does
>   the maths if needed.
>
>   The only time devices should
>   supply raw without scale is if their is no direct transform ( e.g. an infrared
>   intensity measure where only known transform involves combining it with
>   another signal) or their is an external unknown (e.g. proximity sensors where
>   you have to know what they were close to in order to know the scaling!)
>
> If there is a conventional ADC driver not providing either processed directly or
>   both raw and scale let us know and we will fix it!
>

Thanks, I will recycle this patch to use processed only.