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Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Fri, 21 Jul 2023 07:00:12 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     werneazc@gmail.com
Cc:     jdelvare@suse.com, krzysztof.kozlowski+dt@linaro.org,
        conor+dt@kernel.org, robh+dt@kernel.org,
        linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Andre Werner <andre.werner@systec-electronic.com>
Subject: Re: [PATCH v4 2/2] hwmon: (hs3001) Add driver for Renesas HS3001
Message-ID: <48baf05b-8a6c-487f-853f-2e774765f645@roeck-us.net>
References: <20230721100519.597-2-andre.werner@systec-electronic.com>
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In-Reply-To: <20230721100519.597-2-andre.werner@systec-electronic.com>
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On Fri, Jul 21, 2023 at 12:05:19PM +0200, werneazc@gmail.com wrote:
> From: Andre Werner <andre.werner@systec-electronic.com>
> 
> Add base support for Renesas HS3001 temperature
> and humidity sensors and its compatibles HS3002,
> HS3003 and HS3004.
> 
> The sensor has a fix I2C address 0x44. The resolution
> is fixed to 14bit (ref. Missing feature).
> 
> Missing feature:
> - Accessing non-volatile memory: Custom board has no
>   possibility to control voltage supply of sensor. Thus,
>   we cannot send the necessary control commands within
>   the first 10ms after power-on.
> 
> Signed-off-by: Andre Werner <andre.werner@systec-electronic.com>
> 
> ---
> Changelog:
> v1: Initial version
> v2: Extensive refactoring following recommendations of reviewers:
>  - Delete unused defines and device properties. These are added in
>    the initial version because the device supports a programming mode,
>    but I was not able to implement it, because the custom board was
>    not able to control the power supply of the device and so I cannot
>    enter the programming mode of the device.
>  - Correct misunderstanding comments for defines.
>  - Delete mutexes for data and I2C bus accesses.
>  - Replace attributes with recommended chip-info structure. In the
>    initial version I followed the sth3x.c implementation that uses
>    files and attributes in sysfs. The show functions are replaced by
>    is_visible and read callbacks from the HWMON ABI. I also  delete pointless
>    function argument checks.
>  - Correct Yoda programming.
>  - Refactor probe function and delete sleep and measurement of humidity
>    and temperature in probe function. I kept an initial I2C
>    communication to ensure that the device is accessible during probe.
>  - Reduce the number of attributes to humidity and temperature input.
>  v3: Delete chip data because it is unused.
>  v4: Refactor driver as follows:
>  - Delete further unused defines
>  - Replace masks and operations with GENMASK and FIELD_GET macros
>  - Add mutex to protect chip wakeup and data transfer operations on bus
>  - Reformat driver as requested
>  - Make hs3001_is_visible and hs3001_read function static
> ---
>  Documentation/hwmon/hs3001.rst |  37 +++++
>  MAINTAINERS                    |   6 +
>  drivers/hwmon/Kconfig          |  10 ++
>  drivers/hwmon/Makefile         |   1 +
>  drivers/hwmon/hs3001.c         | 250 +++++++++++++++++++++++++++++++++
>  5 files changed, 304 insertions(+)
>  create mode 100644 Documentation/hwmon/hs3001.rst
>  create mode 100644 drivers/hwmon/hs3001.c
> 
> diff --git a/Documentation/hwmon/hs3001.rst b/Documentation/hwmon/hs3001.rst
> new file mode 100644
> index 000000000000..703fb9c45313
> --- /dev/null
> +++ b/Documentation/hwmon/hs3001.rst
> @@ -0,0 +1,37 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +Kernel driver HS3001
> +===================
> +
> +Supported chips:
> +
> +  * Renesas HS3001, HS3002, HS3003, HS3004
> +
> +    Prefix: 'hs3001'
> +
> +    Addresses scanned: -
> +
> +    Datasheet: https://www.renesas.com/us/en/document/dst/hs300x-datasheet?r=417401
> +
> +Author:
> +
> +  - Andre Werner <andre.werner@systec-electronic.com>
> +
> +Description
> +-----------
> +
> +This driver implements support for the Renesas HS3001 chips, a humidity
> +and temperature family. Temperature is measured in degrees celsius, relative
> +humidity is expressed as a percentage. In the sysfs interface, all values are
> +scaled by 1000, i.e. the value for 31.5 degrees celsius is 31500.
> +
> +The device communicates with the I2C protocol. Sensors have the I2C
> +address 0x44 by default.
> +
> +sysfs-Interface
> +---------------
> +
> +===============================================================================
> +temp1_input:        temperature input
> +humidity1_input:    humidity input
> +===============================================================================
> diff --git a/MAINTAINERS b/MAINTAINERS
> index aee340630eca..25d5282b43aa 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9494,6 +9494,12 @@ S:	Maintained
>  W:	http://artax.karlin.mff.cuni.cz/~mikulas/vyplody/hpfs/index-e.cgi
>  F:	fs/hpfs/
>  
> +HS3001 Hardware Temperature and Humidity Sensor
> +M:	Andre Werner <andre.werner@systec-electronic.com>
> +L:	linux-hwmon@vger.kernel.org
> +S:	Maintained
> +F:	drivers/hwmon/hs3001.c
> +
>  HSI SUBSYSTEM
>  M:	Sebastian Reichel <sre@kernel.org>
>  S:	Maintained
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 307477b8a371..ca6be5a23271 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -734,6 +734,16 @@ config SENSORS_HIH6130
>  	  This driver can also be built as a module. If so, the module
>  	  will be called hih6130.
>  
> +config SENSORS_HS3001
> +	tristate "Renesas HS3001 humidity and temperature sensors"
> +	depends on I2C
> +	help
> +	  If you say yes here you get support for the Renesas HS3001,
> +	  to HS3004 humidity and temperature sensors.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called hs3001.
> +
>  config SENSORS_IBMAEM
>  	tristate "IBM Active Energy Manager temperature/power sensors and control"
>  	select IPMI_SI
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 3f4b0fda0998..cdae4e1fc919 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -86,6 +86,7 @@ obj-$(CONFIG_SENSORS_GSC)	+= gsc-hwmon.o
>  obj-$(CONFIG_SENSORS_GPIO_FAN)	+= gpio-fan.o
>  obj-$(CONFIG_SENSORS_GXP_FAN_CTRL) += gxp-fan-ctrl.o
>  obj-$(CONFIG_SENSORS_HIH6130)	+= hih6130.o
> +obj-$(CONFIG_SENSORS_HS3001)	+= hs3001.o
>  obj-$(CONFIG_SENSORS_ULTRA45)	+= ultra45_env.o
>  obj-$(CONFIG_SENSORS_I5500)	+= i5500_temp.o
>  obj-$(CONFIG_SENSORS_I5K_AMB)	+= i5k_amb.o
> diff --git a/drivers/hwmon/hs3001.c b/drivers/hwmon/hs3001.c
> new file mode 100644
> index 000000000000..483b47c81b83
> --- /dev/null
> +++ b/drivers/hwmon/hs3001.c
> @@ -0,0 +1,250 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * This is a non-complete driver implementation for the
> + * HS3001 humidity and temperature sensor and compatibles. It does not include
> + * the configuration possibilities, where it needs to be set to 'programming mode'
> + * during power-up.
> + *
> + *
> + * Copyright (C) 2023 SYS TEC electronic AG
> + * Author: Andre Werner <andre.werner@systec-electronic.com>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/hwmon.h>
> +#include <linux/i2c.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +
> +/* Measurement times */
> +#define HS3001_WAKEUP_TIME	100	/* us */
> +#define HS3001_8BIT_RESOLUTION	550	/* us */
> +#define HS3001_10BIT_RESOLUTION	1310	/* us */
> +#define HS3001_12BIT_RESOLUTION	4500	/* us */
> +#define HS3001_14BIT_RESOLUTION	16900	/* us */
> +
> +#define HS3001_RESPONSE_LENGTH	4
> +
> +#define HS3001_FIXPOINT_ARITH	1000U
> +
> +#define HS3001_MASK_HUMIDITY_0X3FFF	GENMASK(13, 0)
> +#define HS3001_MASK_STATUS_0XC0	GENMASK(7, 6)
> +
> +/* Definitions for Status Bits of A/D Data */
> +#define HS3001_DATA_VALID	0x00	/* Valid Data */
> +#define HS3001_DATA_STALE	0x01	/* Stale Data */
> +
> +struct hs3001_data {
> +	struct i2c_client *client;
> +	struct mutex i2c_lock; /* lock for sending i2c commands */
> +	u32 wait_time;		/* in us */
> +	int temperature;	/* in milli degree */
> +	u32 humidity;		/* in milli % */
> +};
> +
> +static int hs3001_extract_temperature(u16 raw)
> +{
> +	/* fixpoint arithmetic 1 digit */
> +	int temp = (raw >> 2) * HS3001_FIXPOINT_ARITH;
> +
> +	temp /= (1 << 14) - 1;
> +
> +	return temp * 165 - 40 * HS3001_FIXPOINT_ARITH;

This code results in unnecessary precision loss.
Code such as

	unsigned int temp = (raw >> 2) * HS3001_FIXPOINT_ARITH * 165;

	temp /= (1 << 14) - 1;

	return (int)temp - 40 * HS3001_FIXPOINT_ARITH;

would be functionally identical and avoid the precision loss. 


> +}
> +
> +static u32 hs3001_extract_humidity(u16 raw)
> +{
> +	u32 hum = (raw & HS3001_MASK_HUMIDITY_0X3FFF) * HS3001_FIXPOINT_ARITH;
> +
> +	hum /= (1 << 14) - 1;
> +
> +	return hum * 100;

This code results in unnecessary precision loss.
Code such as

	u32 hum = (raw & HS3001_MASK_HUMIDITY_0X3FFF) * HS3001_FIXPOINT_ARITH * 100;

	return hum / (1 << 14) - 1;

would be functionally identical and avoid the precision loss.

If you explicitly _want_ the precision loss in those functions,
please add comments explaining the reason.

> +}
> +
> +static int hs3001_data_fetch_command(struct i2c_client *client,
> +				     struct hs3001_data *data)
> +{
> +	int ret;
> +	u8 buf[HS3001_RESPONSE_LENGTH];
> +	u8 hs3001_status;
> +
> +	ret = i2c_master_recv(client, buf, HS3001_RESPONSE_LENGTH);
> +	if (ret != HS3001_RESPONSE_LENGTH) {
> +		ret = ret < 0 ? ret : -EIO;
> +		dev_dbg(&client->dev,
> +			"Error in i2c communication. Error code: %d.\n", ret);
> +		return ret;
> +	}
> +
> +	hs3001_status = FIELD_GET(HS3001_MASK_STATUS_0XC0, buf[0]);
> +	if (hs3001_status == HS3001_DATA_STALE) {
> +		dev_dbg(&client->dev, "Sensor busy.\n");
> +		return -EBUSY;
> +	}
> +	if (hs3001_status != HS3001_DATA_VALID) {
> +		dev_dbg(&client->dev, "Data invalid.\n");
> +		return -EIO;
> +	}
> +
> +	data->humidity =
> +		hs3001_extract_humidity(be16_to_cpup((__be16 *)&buf[0]));
> +	data->temperature =
> +		hs3001_extract_temperature(be16_to_cpup((__be16 *)&buf[2]));
> +
> +	return 0;
> +}
> +
> +static umode_t hs3001_is_visible(const void *data, enum hwmon_sensor_types type,
> +				 u32 attr, int channel)
> +{
> +	/* Both, humidity and temperature can only be read. */
> +	return 0444;
> +}
> +
> +static int hs3001_read(struct device *dev, enum hwmon_sensor_types type,
> +		       u32 attr, int channel, long *val)
> +{
> +	struct hs3001_data *data = dev_get_drvdata(dev);
> +	struct i2c_client *client = data->client;
> +	int ret;
> +
> +	/* Protected section beginn */
> +	mutex_lock(&data->i2c_lock);
> +	ret = i2c_master_send(client, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * Sensor needs some time to process measurement depending on
> +	 * resolution (ref. datasheet)
> +	 */
> +	fsleep(data->wait_time);
> +
> +	ret = hs3001_data_fetch_command(client, data);
> +	mutex_unlock(&data->i2c_lock);
> +	/* Protected section end */
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	switch (type) {
> +	case hwmon_temp:
> +		switch (attr) {
> +		case hwmon_temp_input:
> +			*val = data->temperature;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +		break;
> +	case hwmon_humidity:
> +		switch (attr) {
> +		case hwmon_humidity_input:
> +			*val = data->humidity;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct hwmon_channel_info *hs3001_info[] = {
> +	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
> +	HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
> +	NULL
> +};
> +
> +static const struct hwmon_ops hs3001_hwmon_ops = {
> +	.is_visible = hs3001_is_visible,
> +	.read = hs3001_read,
> +};
> +
> +static const struct hwmon_chip_info hs3001_chip_info = {
> +	.ops = &hs3001_hwmon_ops,
> +	.info = hs3001_info,
> +};
> +
> +/* device ID table */
> +static const struct i2c_device_id hs3001_ids[] = {
> +	{ "hs3001", 0 },
> +	{ },
> +};
> +
> +MODULE_DEVICE_TABLE(i2c, hs3001_ids);
> +
> +static const struct of_device_id hs3001_of_match[] = {
> +	{.compatible = "renesas,hs3001"},
> +	{ },
> +};
> +
> +MODULE_DEVICE_TABLE(of, hs3001_of_match);
> +
> +static int hs3001_probe(struct i2c_client *client)
> +{
> +	struct hs3001_data *data;
> +	struct device *hwmon_dev;
> +	struct device *dev = &client->dev;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> +		return -EOPNOTSUPP;
> +
> +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->client = client;
> +
> +	/*
> +	 * Measurement time = wake-up time + measurement time temperature
> +	 * + measurment time humidity. This is currently static, because
> +	 * enabling programming mode is not supported, yet.
> +	 */
> +	data->wait_time = (HS3001_WAKEUP_TIME + HS3001_14BIT_RESOLUTION +
> +			   HS3001_14BIT_RESOLUTION);
> +
> +	mutex_init(&data->i2c_lock);
> +
> +	/* Test access to device */
> +	ret = i2c_master_send(client, NULL, 0);
> +	if (ret)
> +		return ret;

Again, this code only checks if a device is there, not that a HS300{1,2,3,4}
is there. It does not add any value, we don't do this for other chips,
and I won't accept this kind of code. Please drop.

Guenter

> +
> +	hwmon_dev = devm_hwmon_device_register_with_info(dev,
> +							 client->name,
> +							 data,
> +							 &hs3001_chip_info,
> +							 NULL);
> +
> +	if (IS_ERR(hwmon_dev))
> +		return dev_err_probe(dev, PTR_ERR(hwmon_dev),
> +				     "Unable to register hwmon device.\n");
> +
> +	return 0;
> +}
> +
> +static struct i2c_driver hs3001_i2c_driver = {
> +	.driver = {
> +		   .name = "hs3001",
> +		   .of_match_table = hs3001_of_match,
> +	},
> +	.probe_new = hs3001_probe,
> +	.id_table = hs3001_ids,
> +};
> +
> +module_i2c_driver(hs3001_i2c_driver);
> +
> +MODULE_AUTHOR("Andre Werner <andre.werner@systec-electronic.com>");
> +MODULE_DESCRIPTION("HS3001 humidity and temperature sensor base driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.41.0
>