Date:	Tue, 19 Apr 2016 20:02:52 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Laxman Dewangan <ldewangan@...dia.com>, robh@...nel.org,
	edubezval@...il.com, rui.zhang@...el.com, mark.rutland@....com,
	pawel.moll@....com, ijc+devicetree@...lion.org.uk
Cc:	linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH V4 2/2] thermal: generic-adc: Add ADC based thermal sensor
 driver

On 19/04/16 08:22, 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@...dia.com>
Acked-by: Jonathan Cameron <jic23@...nel.org> primarily for the IIO
side of things.
> 
> ---
> 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.
> 
> Changes from V3:
> - Jonathan suggested to use the iio_channel_read_processed only. Making
>   changes accordingly.
> ---
>  drivers/thermal/Kconfig               |  10 ++
>  drivers/thermal/Makefile              |   1 +
>  drivers/thermal/thermal-generic-adc.c | 182 ++++++++++++++++++++++++++++++++++
>  3 files changed, 193 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..73f55d6
> --- /dev/null
> +++ b/drivers/thermal/thermal-generic-adc.c
> @@ -0,0 +1,182 @@
> +/*
> + * Generic ADC thermal driver
> + *
> + * Copyright (C) 2016 NVIDIA CORPORATION. All rights reserved.
> + *
> + * Author: Laxman Dewangan <ldewangan@...dia.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_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 = iio_read_channel_processed(gti->channel, &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@...dia.com>");
> +MODULE_DESCRIPTION("Generic ADC thermal driver using IIO framework with DT");
> +MODULE_LICENSE("GPL v2");
> 

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