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Date: Thu, 01 May 2014 19:06:33 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Tomas Pop <tomas.pop.mff@...il.com>,
"jdelvare@...e.de" <jdelvare@...e.de>
CC: lm-sensors@...sensors.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH v2] hwmon: add support for Sensirion SHTC1 sensor
On 05/01/2014 04:05 PM, Tomas Pop wrote:
> One more time this patch sent with correct settings of my email client
> - I'm sorry for this.
>
> This is a second version of the driver for Sensirion SHTC1 humidity and
> temperature sensor. Initial version was submitted in July 2012.
> http://www.gossamer-threads.com/lists/linux/kernel/1569130#1569130
>
> We included suggested corrections formerly discussed in this list after
> initial submission, but since it is quite a while, we are re-submitting
> it again as a request for comments. Here is a list of important changes
> to the initial version:
>
> * returning real error codes instead of -1 or -ENODEV
> * using boolean variables instead of bitmaps where possible
> * macros be16_to_cpup used for conversion of indianneess
> * corrected formula for decoding of humidity and temperature values
> * documentation update
>
> Patch was generated against kernel v3.15-rc3
>
> Signed-off-by: Tomas Pop <tomas.pop@...sirion.com>
> ---
> Documentation/hwmon/shtc1 | 38 +++++
> drivers/hwmon/Kconfig | 10 ++
> drivers/hwmon/Makefile | 1 +
> drivers/hwmon/shtc1.c | 323 ++++++++++++++++++++++++++++++++++++
> include/linux/platform_data/shtc1.h | 24 +++
> 5 files changed, 396 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..6a72ae2d
> --- /dev/null
> +++ b/Documentation/hwmon/shtc1
> @@ -0,0 +1,38 @@
> +Kernel driver shtc1
> +===================
> +
> +Supported chips:
> + * Sensirion SHTC1
> + Prefix: 'shtc1'
> + Addresses scanned: none
> + Datasheet: Publicly available at the Sensirion website
> + http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_SHTC1_Datasheet.pdf
Ok to add SHTW1 here if it is known to work.
Just say:
Datasheet: Not publicly available
> +
> +Author:
> + Johannes Winkelmann <johannes.winkelmann@...sirion.com>
> +
> +Description
> +-----------
> +
> +This driver implements support for the Sensirion SHTC1 chip, a humidity and
Two spaces
> +temperature sensor. Temperature is measured in degrees celsius, relative
> +humidity is expressed as a percentage. Driver can be used as well for SHTW1
> +chip, that has the same electrical interface, but datasheet has not been
... for SHTW1, which has the same electrical interface.
> +yet published.
> +
Either add support for the second now, or don't mention it at all
(especially if the chip has a different ID and you don't want to add
that ID at this point for some reason).
> +The device communicates with the I2C protocol. All sensors are set to the same
... are set to I2C address 0x70.
> +I2C address 0x70, so an entry with I2C_BOARD_INFO("shtc1", 0x70) can be used
> +in the board setup code. See Documentation/i2c/instantiating-devices for
> +other methods to instantiate the device.
> +
I would suggest to just refer to the instantiating-devices document and drop
the I2C_BOARD_INFO example.
> +Furthermore, there are two configuration options by means of platform_data:
options configurable by means ...
> +1. blocking (pull the I2C clock line down while performing the measurement) or
> + non-blocking, mode. Blocking mode will guarantee the fastest result, but
non-blocking mode (no comma)
> + the I2C bus will be busy during that time
that time.
> +2. high or low accuracy. Using high accuracy is always recommended.
> +
> +sysfs-Interface
> +---------------
> +
> +temp1_input - temperature input
> +humidity1_input - humidity input
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index bc196f4..4d58149 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1114,6 +1114,16 @@ 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."
> + depends on I2C
> + help
> + If you say yes here you get support for the Sensiron SHTC1 humidity
and SHTW1 ?
> + and temperature sensor.
> +
> + 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/Makefile b/drivers/hwmon/Makefile
> index c48f987..1cc5273 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -125,6 +125,7 @@ obj-$(CONFIG_SENSORS_SCH5627) += sch5627.o
> obj-$(CONFIG_SENSORS_SCH5636) += sch5636.o
> obj-$(CONFIG_SENSORS_SHT15) += sht15.o
> obj-$(CONFIG_SENSORS_SHT21) += sht21.o
> +obj-$(CONFIG_SENSORS_SHTC1) += shtc1.o
> obj-$(CONFIG_SENSORS_SIS5595) += sis5595.o
> obj-$(CONFIG_SENSORS_SMM665) += smm665.o
> obj-$(CONFIG_SENSORS_SMSC47B397)+= smsc47b397.o
> diff --git a/drivers/hwmon/shtc1.c b/drivers/hwmon/shtc1.c
> new file mode 100644
> index 0000000..96d398b
> --- /dev/null
> +++ b/drivers/hwmon/shtc1.c
> @@ -0,0 +1,323 @@
> +/* Sensirion SHTC1 humidity and temperature sensor driver
> + *
> + * Copyright (C) 2012 Sensirion AG, Switzerland
2014 ?
> + * Author: Johannes Winkelmann <johannes.winkelmann@...sirion.com>
> + *
Is Johannes still involved ?
> + * 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.
> + *
> + * Data sheet available soon
> + * TODO: add link
Datasheet is referenced in documentation, so you don't need the link here.
Better to keep it in one please, then there is only one place to change
if it needs to be updated.
> + */
> +
> +#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 and constants for reading the ID register */
> +static const unsigned char shtc1_cmd_read_id_reg[] = { 0xef, 0xc8 };
> +static const unsigned char shtc1_id_reg_content = 0x07;
> +static const unsigned char shtc1_id_reg_mask = 0x1f;
> +
Please use defines here. There is no benefit to have one-byte constants.
If the W1 chip has a different ID, you might as well add it in now and detect it.
> +/* delays for non-blocking i2c commands */
> +/* TODO: use max timings */
> +#define SHTC1_NONBLOCKING_WAIT_TIME_HPM 10
> +#define SHTC1_NONBLOCKING_WAIT_TIME_LPM 1
delay in what ? ms ? us ? seconds ?
Please specify.
> +
> +#define SHTC1_CMD_LENGTH 2
> +#define SHTC1_RESPONSE_LENGTH 6
> +
> +struct shtc1_data {
> + struct device *hwmon_dev;
> + struct mutex update_lock;
> + bool valid;
> + unsigned long last_updated; /* In jiffies */
> +
> + const unsigned char *command;
> + unsigned int nonblocking_wait_time;
> +
> + struct shtc1_platform_data setup;
> +
> + int temperature;
> + int humidity;
> +};
> +
> +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;
> + }
> +}
> +
Please move this function down, just before the probe function.
> +static int shtc1_update_values(struct i2c_client *client,
> + struct shtc1_data *data,
> + char *buf,
> + int bufsize)
Please align continuation lines with (, and limit the number of continuation lines
where possible (eg, buf and bufsize fit into one line).
> +{
> + int ret = i2c_master_send(client, data->command, SHTC1_CMD_LENGTH);
> + if (ret < 0) {
> + dev_err(&client->dev, "failed to send command: %d", ret);
Newline missing.
> + return ret;
> + }
There is another error condition: the function returns the number of bytes written,
which can be smaller than SHTC1_CMD_LENGTH.
> +
> + /*
> + * 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, thus the msleep().
> + *
> + * TODO: consider usleep_range
Please do ... and fix all the other TODOs in case I missed any.
> + */
> + if (!data->setup.blocking_io)
> + msleep(data->nonblocking_wait_time);
> +
> + ret = i2c_master_recv(client, buf, bufsize);
> + if (ret != bufsize) {
> + dev_err(&client->dev, "failed to read values: %d", ret);
Newline.
The return value can be >= 0, meaning the calling code can get confused.
Please make sure that the function always returns a valid error code.
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +/* sysfs attributes */
> +static struct shtc1_data *shtc1_update_client(struct device *dev)
> +{
> + struct i2c_client *client = to_i2c_client(dev);
> + struct shtc1_data *data = i2c_get_clientdata(client);
> +
> + unsigned char buf[SHTC1_RESPONSE_LENGTH];
> + int val;
> + int ret;
> +
> + mutex_lock(&data->update_lock);
> +
> + /*
> + * Initialize 'ret' in case we had a valid result before, but
> + * read too quickly in which case we return the last values.
> + */
> + ret = !data->valid;
So ret gets pre-initialized with 1 if valid == 0. Doesn't really make sense.
Just initialize it with 0 above.
int ret = 0;
> +
> + if (time_after(jiffies, data->last_updated + HZ / 10) || !data->valid) {
> + ret = shtc1_update_values(client, data, buf, sizeof(buf));
> +
Unnecessary empty line.
> + 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));
Spaces before and after '+'
Just wondering .. what is in buf[2] and buf[5] ?
> + data->humidity = ((12500 * val) >> 13);
> +
> + data->last_updated = jiffies;
> + data->valid = 1;
= true;
> + }
> +
> +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 SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
> + shtc1_show_temperature, NULL, 0);
> +static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
> + shtc1_show_humidity, NULL, 0);
You don't need SENSOR_DEVICE_ATTR here. DEVICE_ATTR is sufficient.
Another option would be to store temperature and humidity in an array
and use the last parameter of SENSOR_DEVICE_ATTR to index the array.
This way you would only need a single show function. I'll leave
that up to you.
> +
> +static struct attribute *shtc1_attributes[] = {
> + &sensor_dev_attr_temp1_input.dev_attr.attr,
> + &sensor_dev_attr_humidity1_input.dev_attr.attr,
> + NULL
> +};
> +
> +static const struct attribute_group shtc1_attr_group = {
> + .attrs = shtc1_attributes,
> +};
Please use ATTRIBUTE_GROUPS().
> +
> +static int shtc1_probe(struct i2c_client *client,
> + const struct i2c_device_id *id)
> +{
> + struct shtc1_data *data;
A local variable
struct device *dev = &client->dev;
would save you a number of dereference operations.
> + int err;
> + struct i2c_adapter *adap = client->adapter;
> + char id_reg[2];
> +
> + if (!i2c_check_functionality(adap, I2C_FUNC_I2C)) {
> + dev_err(&client->dev,
> + "adapter does not support plain i2c transactions\n");
> + return -ENODEV;
> + }
> +
> + err = i2c_master_send(client, shtc1_cmd_read_id_reg, SHTC1_CMD_LENGTH);
> +
Please no empty lines before error checks.
> + if (err < 0) {
Also err != SHTC1_CMD_LENGTH.
> + dev_err(&client->dev, "could not send read command: %d\n", err);
> + return -ENODEV;
> + }
> + err = i2c_master_recv(client, id_reg, sizeof(id_reg));
> + if (err != sizeof(id_reg)) {
> + dev_err(&client->dev, "could not read ID register: %d\n", err);
> + return -ENODEV;
> + }
> + if ((id_reg[1] & shtc1_id_reg_mask) != shtc1_id_reg_content) {
> + dev_err(&client->dev, "ID register doesn't match\n");
> + return -ENODEV;
> + }
> +
> + data = devm_kzalloc(&client->dev, sizeof(struct shtc1_data),
sizeof(*data) is preferred.
> + GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + /* defaults: blocking, high precision mode */
> + data->setup.blocking_io = 1;
> + data->setup.high_precision = 1;
> +
= true;
for both.
> + if (client->dev.platform_data)
> + data->setup = *(struct shtc1_platform_data *)client->dev.platform_data;
> + shtc1_select_command(data);
> +
> + i2c_set_clientdata(client, data);
> + mutex_init(&data->update_lock);
> +
> + err = sysfs_create_group(&client->dev.kobj, &shtc1_attr_group);
> + if (err) {
> + dev_dbg(&client->dev, "could not create sysfs files\n");
> + goto fail_free;
> + return err;
goto or return, but not both (doesn't this create a warning about unreachable code ?).
goto is unnecessary, actually. return err is just fine.
> + }
> + data->hwmon_dev = hwmon_device_register(&client->dev);
Please use devm_hwmon_device_register_with_groups().
struct device *hwmon_dev;
...
hwmon_dev = devm_hwmon_device_register_with_groups(&client->dev, client->name,
data, sht1c_groups);
return PTR_ERR_OR_ZERO(hwmon_dev);
> + if (IS_ERR(data->hwmon_dev)) {
> + dev_dbg(&client->dev, "unable to register hwmon device\n");
> + err = PTR_ERR(data->hwmon_dev);
> + goto fail_remove_sysfs;
> + }
> +
> +
No more than one empty line, please.
> + dev_info(&client->dev, "initialized\n");
Unnecessary noise.
> +
> + return 0;
> +
> +fail_remove_sysfs:
> + sysfs_remove_group(&client->dev.kobj, &shtc1_attr_group);
> +fail_free:
> + kfree(data);
Unnecessary kfree.
> +
> + return err;
> +}
> +
> +/**
> + * shtc1_remove() - remove device
> + * @client: I2C client device
> + */
> +static int shtc1_remove(struct i2c_client *client)
> +{
> + struct shtc1_data *data = i2c_get_clientdata(client);
> +
> + hwmon_device_unregister(data->hwmon_dev);
> + sysfs_remove_group(&client->dev.kobj, &shtc1_attr_group);
> +
> + return 0;
> +}
You can drop this entire function with the new hwmon API.
> +
> +/* device ID table */
> +static const struct i2c_device_id shtc1_id[] = {
> + { "shtc1", 0 },
> + { }
> +};
> +MODULE_DEVICE_TABLE(i2c, shtc1_id);
> +
> +static struct i2c_driver shtc1_i2c_driver = {
> + .driver.name = "shtc1",
> + .probe = shtc1_probe,
> + .remove = shtc1_remove,
> + .id_table = shtc1_id,
> +};
> +
> +/**
> + * shtc1_init() - initialize driver
> + *
> + * Called when kernel is booted or module is inserted.
> + * Returns 0 on success.
> + */
> +static int __init shtc1_init(void)
> +{
> + return i2c_add_driver(&shtc1_i2c_driver);
> +}
> +module_init(shtc1_init);
> +
> +/*
> + * shtc1_exit() - clean up driver
> + *
> + * Called when module is removed.
> + */
> +static void __exit shtc1_exit(void)
> +{
> + i2c_del_driver(&shtc1_i2c_driver);
> +}
> +
> +module_exit(shtc1_exit);
Please use module_i2c_driver().
> +
> +
> +MODULE_AUTHOR("Johannes Winkelmann <johannes.winkelmann@...sirion.com>");
> +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..4629364
> --- /dev/null
> +++ b/include/linux/platform_data/shtc1.h
> @@ -0,0 +1,24 @@
> +/*
> + * Copyright (C) 2012 Sensirion AG, Switzerland
2014 ?
> + * Author: Johannes Winkelmann <johannes.winkelmann@...sirion.com>
> + *
> + * 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;
> +};
> +
Please no empty line at the end.
Wondering ... do you plan to implement devicetree support (or have customers who need it) ?
I could imagine that a chip like this will be used, for example, on beagleboard, which would
require devicetree support.
Thanks,
Guenter
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