Re: [PATCH v3] hwmon: add support for Sensirion SHTC1 sensor

[Guenter Roeck]

On Mon, Jun 02, 2014 at 03:13:40PM -0700, Tomas Pop wrote:
> Hi Guenter,
> 
Hi Tomas,

comments inline. Mostly nitpicks plus one real bug.

> here is a third version of the driver for Sensirion SHTC1 humidity and
> temperature sensor. We included suggested corrections, the most important
> changes to the previous version are:
> 
> * default mode of I2C communication is changed to non-blocking
> * default values of configuration added to documentation
> * driver uses new ABI to obtain shtc1_data* and i2c_client*
> 
> The patch was generated against kernel v3.14.4 (the version used for testing),
> but the patch can be applied smoothly also to v3.15-rc8.
> 
> Signed-off-by: Tomas Pop <tomas.pop@xxxxxxxxxxxxx>
> 
> ---

In general, you'll want a description of the patch prior to the --- line (this
is what is added to the commit log), and everything that should not be part of
the commit log below the --- line.

>  Documentation/hwmon/shtc1           |  44 +++++++
>  drivers/hwmon/Kconfig               |  10 ++
>  drivers/hwmon/shtc1.c               | 252 ++++++++++++++++++++++++++++++++++++
>  include/linux/platform_data/shtc1.h |  23 ++++
>  4 files changed, 329 insertions(+)
>  create mode 100644 Documentation/hwmon/shtc1
>  create mode 100644 drivers/hwmon/shtc1.c
>  create mode 100644 include/linux/platform_data/shtc1.h
> 
> diff --git a/Documentation/hwmon/shtc1 b/Documentation/hwmon/shtc1
> new file mode 100644
> index 0000000..6bf00a4
> --- /dev/null
> +++ b/Documentation/hwmon/shtc1
> @@ -0,0 +1,44 @@
> +Kernel driver shtc1
> +===================
> +
> +Supported chips:
> +  * Sensirion SHTC1
> +    Prefix: 'shtc1'
> +    Addresses scanned: none
> +    Datasheet: Publicly available at the Sensirion website

Since you have a pointer to the datasheet you don't need the "Publicly available".

> +    http://www.sensirion.com/file/datasheet_shtc1
> +
> +  * Sensirion SHTW1
> +    Prefix: 'shtc1'

I ould suggest to use shtw1 here. This lets users instantiate this chip with the
correct ID. That is especially useful if instantiated through devicetree.
Also see below.

> +    Addresses scanned: none
> +    Datasheet: Not publicly available
> +
> +Author:
> +  Johannes Winkelmann <johannes.winkelmann@xxxxxxxxxxxxx>
> +
> +Description
> +-----------
> +
> +This driver implements support for the Sensirion SHTC1 chip, a humidity and
> +temperature sensor. Temperature is measured in degrees celsius, relative
> +humidity is expressed as a percentage. Driver can be used as well for SHTW1
> +chip, which has the same electrical interface.
> +
> +The device communicates with the I2C protocol. All sensors are set to I2C
> +address 0x70. See Documentation/i2c/instantiating-devices for methods to
> +instantiate the device.
> +
> +There are two options configurable by means of shtc1_platform_data:
> +1. blocking (pull the I2C clock line down while performing the measurement) or
> +   non-blocking mode. Blocking mode will guarantee the fastest result but
> +   the I2C bus will be busy during that time. By default, non-blocking mode
> +   is used. Make sure clock-stretching works properly on your device if you
> +   want to use blocking mode.
> +2. high or low accuracy. High accuracy is used by default and using it is
> +   strongly recommended.
> +
> +sysfs-Interface
> +---------------
> +
> +temp1_input - temperature input
> +humidity1_input - humidity input
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 193c496..bf06213 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1047,6 +1047,16 @@ config SENSORS_SHT21
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called sht21.
>  
> +config SENSORS_SHTC1
> +	tristate "Sensiron humidity and temperature sensors. SHTC1 and compat."

How about "Sensirion SHTC1 and compatible humidity and temperature sensors" ?

> +	depends on I2C
> +	help
> +	  If you say yes here you get support for the Sensiron SHTC1 and SHTW1
> +	  humidity and temperature sensor.
> +
				sensors

> +	  This driver can also be built as a module.  If so, the module
> +	  will be called shtc1.
> +
>  config SENSORS_S3C
>  	tristate "Samsung built-in ADC"
>  	depends on S3C_ADC
> diff --git a/drivers/hwmon/shtc1.c b/drivers/hwmon/shtc1.c
> new file mode 100644
> index 0000000..b3278ab
> --- /dev/null
> +++ b/drivers/hwmon/shtc1.c
> @@ -0,0 +1,252 @@
> +/* Sensirion SHTC1 humidity and temperature sensor driver
> + *
> + * Copyright (C) 2014 Sensirion AG, Switzerland
> + * Author: Johannes Winkelmann <johannes.winkelmann@xxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/i2c.h>
> +#include <linux/hwmon.h>
> +#include <linux/hwmon-sysfs.h>
> +#include <linux/err.h>
> +#include <linux/delay.h>
> +#include <linux/platform_data/shtc1.h>
> +
> +/* commands (high precision mode) */
> +static const unsigned char shtc1_cmd_measure_blocking_hpm[]    = { 0x7C, 0xA2 };
> +static const unsigned char shtc1_cmd_measure_nonblocking_hpm[] = { 0x78, 0x66 };
> +
> +/* commands (low precision mode) */
> +static const unsigned char shtc1_cmd_measure_blocking_lpm[]    = { 0x64, 0x58 };
> +static const unsigned char shtc1_cmd_measure_nonblocking_lpm[] = { 0x60, 0x9c };
> +
> +/* command for reading the ID register */
> +static const unsigned char shtc1_cmd_read_id_reg[]	       = { 0xef, 0xc8 };
> +
> +/* constants for reading the ID register */
> +#define SHTC1_ID_REG_CONTENT 0x07

How about just SHTC1_ID ? The REG_CONTENT confused me a bit until I got it.

> +#define SHTC1_ID_REG_MASK    0x1f
> +
> +/* delays for non-blocking i2c commands, both in us */
> +#define SHTC1_NONBLOCKING_WAIT_TIME_HPM  14400
> +#define SHTC1_NONBLOCKING_WAIT_TIME_LPM   1000
> +
> +#define SHTC1_CMD_LENGTH      2
> +#define SHTC1_RESPONSE_LENGTH 6
> +
> +struct shtc1_data {
> +	struct device *hwmon_dev;

No longer needed. Also see below.

> +	struct i2c_client *client;
> +	struct mutex update_lock;
> +	bool valid;
> +	unsigned long last_updated; /* in jiffies */
> +
> +	const unsigned char *command;
> +	unsigned int nonblocking_wait_time; /* in us */
> +
> +	struct shtc1_platform_data setup;
> +
> +	int temperature; /* 1000 * temperature in dgr C */
> +	int humidity; /* 1000 * relative humidity in %RH */
> +};
> +
> +static int shtc1_update_values(struct i2c_client *client,
> +			       struct shtc1_data *data,
> +			       char *buf, int bufsize)
> +{
> +	int ret = i2c_master_send(client, data->command, SHTC1_CMD_LENGTH);
> +	if (ret != SHTC1_CMD_LENGTH) {
> +		dev_err(&client->dev, "failed to send command: %d\n", ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	/*
> +	* In blocking mode (clock stretching mode) the I2C bus
> +	* is blocked for other traffic, thus the call to i2c_master_recv()
> +	* will wait until the data is ready. For non blocking mode, we
> +	* have to wait ourselves.
> +	*/

	/*
	 * Multi-line comments should look like this.
	 * Watch the alignment of '*'.
	 */

> +	if (!data->setup.blocking_io)
> +		usleep_range(data->nonblocking_wait_time,
> +			     data->nonblocking_wait_time + 1000);
> +
> +	ret = i2c_master_recv(client, buf, bufsize);
> +	if (ret != bufsize) {
> +		dev_err(&client->dev, "failed to read values: %d\n", ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +/* sysfs attributes */
> +static struct shtc1_data *shtc1_update_client(struct device *dev)
> +{
> +	struct shtc1_data *data = dev_get_drvdata(dev);
> +	struct i2c_client *client = data->client;
> +
Unnecessary empty line.

> +	unsigned char buf[SHTC1_RESPONSE_LENGTH];
> +	int val;
> +	int ret = 0;
> +
> +	mutex_lock(&data->update_lock);
> +
> +	if (time_after(jiffies, data->last_updated + HZ / 10) || !data->valid) {
> +		ret = shtc1_update_values(client, data, buf, sizeof(buf));
> +		if (ret)
> +			goto out;
> +
> +		/*
> +		* From datasheet:
> +		* T = -45 + 175 * ST / 2^16
> +		* RH = 100 * SRH / 2^16
> +		*
> +		* Adapted for integer fixed point (3 digit) arithmetic.
> +		*/
> +		val = be16_to_cpup((__be16 *)buf);
> +		data->temperature = ((21875 * val) >> 13) - 45000;
> +		val = be16_to_cpup((__be16 *)(buf + 3));
> +		data->humidity = ((12500 * val) >> 13);
> +
> +		data->last_updated = jiffies;
> +		data->valid = 1;
> +	}
> +
> +out:
> +	mutex_unlock(&data->update_lock);
> +
> +	return ret == 0 ? data : ERR_PTR(ret);
> +}
> +
> +static ssize_t shtc1_show_temperature(struct device *dev,
> +				      struct device_attribute *attr,
> +				      char *buf)
> +{
> +	struct shtc1_data *data = shtc1_update_client(dev);
> +	if (IS_ERR(data))
> +		return PTR_ERR(data);
> +
> +	return sprintf(buf, "%d\n", data->temperature);
> +}
> +
> +static ssize_t shtc1_show_humidity(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	struct shtc1_data *data = shtc1_update_client(dev);
> +	if (IS_ERR(data))
> +		return PTR_ERR(data);
> +
> +	return sprintf(buf, "%d\n", data->humidity);
> +}
> +
> +static DEVICE_ATTR(temp1_input, S_IRUGO, shtc1_show_temperature, NULL);
> +static DEVICE_ATTR(humidity1_input, S_IRUGO, shtc1_show_humidity, NULL);

Consider using DEVICE_ATTR_RO. You'll have to rename the functions, but it is a
bit less boilerplate.

> +
> +static struct attribute *shtc1_attrs[] = {
> +	&dev_attr_temp1_input.attr,
> +	&dev_attr_humidity1_input.attr,
> +	NULL
> +};
> +
> +ATTRIBUTE_GROUPS(shtc1);
> +
> +static void shtc1_select_command(struct shtc1_data *data)
> +{
> +	if (data->setup.high_precision) {
> +		data->command = data->setup.blocking_io ?
> +				shtc1_cmd_measure_blocking_hpm :
> +				shtc1_cmd_measure_nonblocking_hpm;
> +		data->nonblocking_wait_time = SHTC1_NONBLOCKING_WAIT_TIME_HPM;
> +
> +	} else {
> +		data->command = data->setup.blocking_io ?
> +				shtc1_cmd_measure_blocking_lpm :
> +				shtc1_cmd_measure_nonblocking_lpm;
> +		data->nonblocking_wait_time = SHTC1_NONBLOCKING_WAIT_TIME_LPM;
> +	}
> +}
> +
> +static int shtc1_probe(struct i2c_client *client,
> +		       const struct i2c_device_id *id)
> +{
> +	int ret;
> +	char id_reg[2];
> +	struct shtc1_data *data;
> +	struct device *hwmon_dev;
> +	struct i2c_adapter *adap = client->adapter;
> +	struct device *dev = &client->dev;
> +
> +	if (!i2c_check_functionality(adap, I2C_FUNC_I2C)) {
> +		dev_err(dev, "plain i2c transactions not supported\n");
> +		return -ENODEV;
> +	}
> +
> +	ret = i2c_master_send(client, shtc1_cmd_read_id_reg, SHTC1_CMD_LENGTH);
> +	if (ret != SHTC1_CMD_LENGTH) {
> +		dev_err(dev, "could not send read_id_reg command: %d\n", ret);
> +		return ret < 0 ? ret : -ENODEV;
> +	}
> +	ret = i2c_master_recv(client, id_reg, sizeof(id_reg));
> +	if (ret != sizeof(id_reg)) {
> +		dev_err(dev, "could not read ID register: %d\n", ret);
> +		return -ENODEV;
> +	}
> +	if ((id_reg[1] & SHTC1_ID_REG_MASK) != SHTC1_ID_REG_CONTENT) {
> +		dev_err(dev, "ID register doesn't match\n");
> +		return -ENODEV;
> +	}
> +
> +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->setup.blocking_io = false;
> +	data->setup.high_precision = true;
> +	data->client = client;
> +
> +	if (client->dev.platform_data)
> +		data->setup = *(struct shtc1_platform_data *)dev->platform_data;
> +	shtc1_select_command(data);
> +	mutex_init(&data->update_lock);
> +
> +	hwmon_dev = devm_hwmon_device_register_with_groups(dev,
> +							   client->name,
> +							   data,
> +							   shtc1_groups);
> +	if (IS_ERR(hwmon_dev))
> +		dev_dbg(dev, "unable to register hwmon device\n");
> +
> +	return PTR_ERR_OR_ZERO(data->hwmon_dev);

Got you :-). data->hwmon_dev is always NULL. 's/data->//' would be a good idea
here, and you don't need to keep hwmon_dev in private data anymore.

> +}
> +
> +/* device ID table */
> +static const struct i2c_device_id shtc1_id[] = {
> +	{ "shtc1", 0 },

I would suggest to add
	{ "shtw1", 0 },

to enable instantiation for the second chip (and from devicetree with the
correct chip ID).

> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, shtc1_id);
> +
> +static struct i2c_driver shtc1_i2c_driver = {
> +	.driver.name  = "shtc1",
> +	.probe        = shtc1_probe,
> +	.id_table     = shtc1_id,
> +};
> +
> +module_i2c_driver(shtc1_i2c_driver);
> +
> +MODULE_AUTHOR("Johannes Winkelmann <johannes.winkelmann@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Sensirion SHTC1 humidity and temperature sensor driver");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/platform_data/shtc1.h b/include/linux/platform_data/shtc1.h
> new file mode 100644
> index 0000000..7b8c353
> --- /dev/null
> +++ b/include/linux/platform_data/shtc1.h
> @@ -0,0 +1,23 @@
> +/*
> + * Copyright (C) 2014 Sensirion AG, Switzerland
> + * Author: Johannes Winkelmann <johannes.winkelmann@xxxxxxxxxxxxx>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#ifndef __SHTC1_H_
> +#define __SHTC1_H_
> +
> +struct shtc1_platform_data {
> +	bool blocking_io;
> +	bool high_precision;
> +};
> +#endif /* __SHTC1_H_ */
> -- 
> 1.8.3.2
> 
> 
> 
> 
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