hwmon: Driver for disk and solid state drives with temperature sensors

Reading the temperature of ATA drives has been supported for years
by userspace tools such as smarttools or hddtemp. The downside of
such tools is that they need to run with super-user privilege, that
the temperatures are not reported by standard tools such as 'sensors'
or 'libsensors', and that drive temperatures are not available for use
in the kernel's thermal subsystem.

This driver solves this problem by adding support for reading the
temperature of ATA drives from the kernel using the hwmon API and
by adding a temperature zone for each drive.

With this driver, the hard disk temperature can be read using the
unprivileged 'sensors' application:

$ sensors drivetemp-scsi-1-0
drivetemp-scsi-1-0
Adapter: SCSI adapter
temp1:        +23.0°C

or directly from sysfs:

$ grep . /sys/class/hwmon/hwmon9/{name,temp1_input}
/sys/class/hwmon/hwmon9/name:drivetemp
/sys/class/hwmon/hwmon9/temp1_input:23000

If the drive supports SCT transport and reports temperature limits,
those are reported as well.

drivetemp-scsi-0-0
Adapter: SCSI adapter
temp1:        +27.0°C  (low  =  +0.0°C, high = +60.0°C)
                       (crit low = -41.0°C, crit = +85.0°C)
                       (lowest = +23.0°C, highest = +34.0°C)

The driver attempts to use SCT Command Transport to read the drive
temperature. If the SCT Command Transport feature set is not available,
or if it does not report the drive temperature, drive temperatures may
be readable through SMART attributes. Since SMART attributes are not well
defined, this method is only used as fallback mechanism.

Cc: Chris Healy <cphealy@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

5 files changed, 638 insertions, 0 deletions

diff --git a/Documentation/hwmon/drivetemp.rst b/Documentation/hwmon/drivetemp.rst
new file mode 100644
index 000000000000..2d37d049247f
--- /dev/null
+++ b/Documentation/hwmon/drivetemp.rst
@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver drivetemp
+=======================
+
+
+References
+----------
+
+ANS T13/1699-D
+Information technology - AT Attachment 8 - ATA/ATAPI Command Set (ATA8-ACS)
+
+ANS Project T10/BSR INCITS 513
+Information technology - SCSI Primary Commands - 4 (SPC-4)
+
+ANS Project INCITS 557
+Information technology - SCSI / ATA Translation - 5 (SAT-5)
+
+
+Description
+-----------
+
+This driver supports reporting the temperature of disk and solid state
+drives with temperature sensors.
+
+If supported, it uses the ATA SCT Command Transport feature to read
+the current drive temperature and, if available, temperature limits
+as well as historic minimum and maximum temperatures. If SCT Command
+Transport is not supported, the driver uses SMART attributes to read
+the drive temperature.
+
+
+Sysfs entries
+-------------
+
+Only the temp1_input attribute is always available. Other attributes are
+available only if reported by the drive. All temperatures are reported in
+milli-degrees Celsius.
+
+=======================	=====================================================
+temp1_input		Current drive temperature
+temp1_lcrit		Minimum temperature limit. Operating the device below
+			this temperature may cause physical damage to the
+			device.
+temp1_min		Minimum recommended continuous operating limit
+temp1_max		Maximum recommended continuous operating temperature
+temp1_crit		Maximum temperature limit. Operating the device above
+			this temperature may cause physical damage to the
+			device.
+temp1_lowest		Minimum temperature seen this power cycle
+temp1_highest		Maximum temperature seen this power cycle
+=======================	=====================================================
diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 6f88af43eed6..682ef4dda89c 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -47,6 +47,7 @@ Hardware Monitoring Kernel Drivers
    da9055
    dell-smm-hwmon
    dme1737
+   drivetemp
    ds1621
    ds620
    emc1403
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index e6e1b1008cdd..7ea61648ad16 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -385,6 +385,16 @@ config SENSORS_ATXP1
 	  This driver can also be built as a module. If so, the module
 	  will be called atxp1.
 
+config SENSORS_DRIVETEMP
+	tristate "Hard disk drives with temperature sensors"
+	depends on SCSI && ATA
+	help
+	  If you say yes you get support for the temperature sensor on
+	  hard disk drives.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called satatemp.
+
 config SENSORS_DS620
 	tristate "Dallas Semiconductor DS620"
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 226a1182967a..f0f514f9cf24 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -56,6 +56,7 @@ obj-$(CONFIG_SENSORS_DA9052_ADC)+= da9052-hwmon.o
 obj-$(CONFIG_SENSORS_DA9055)+= da9055-hwmon.o
 obj-$(CONFIG_SENSORS_DELL_SMM)	+= dell-smm-hwmon.o
 obj-$(CONFIG_SENSORS_DME1737)	+= dme1737.o
+obj-$(CONFIG_SENSORS_DRIVETEMP)	+= drivetemp.o
 obj-$(CONFIG_SENSORS_DS620)	+= ds620.o
 obj-$(CONFIG_SENSORS_DS1621)	+= ds1621.o
 obj-$(CONFIG_SENSORS_EMC1403)	+= emc1403.o
diff --git a/drivers/hwmon/drivetemp.c b/drivers/hwmon/drivetemp.c
new file mode 100644
index 000000000000..370d0c74eb01
--- /dev/null
+++ b/drivers/hwmon/drivetemp.c
@@ -0,0 +1,574 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Hwmon client for disk and solid state drives with temperature sensors
+ * Copyright (C) 2019 Zodiac Inflight Innovations
+ *
+ * With input from:
+ *    Hwmon client for S.M.A.R.T. hard disk drives with temperature sensors.
+ *    (C) 2018 Linus Walleij
+ *
+ *    hwmon: Driver for SCSI/ATA temperature sensors
+ *    by Constantin Baranov <const@mimas.ru>, submitted September 2009
+ *
+ * This drive supports reporting the temperatire of SATA drives. It can be
+ * easily extended to report the temperature of SCSI drives.
+ *
+ * The primary means to read drive temperatures and temperature limits
+ * for ATA drives is the SCT Command Transport feature set as specified in
+ * ATA8-ACS.
+ * It can be used to read the current drive temperature, temperature limits,
+ * and historic minimum and maximum temperatures. The SCT Command Transport
+ * feature set is documented in "AT Attachment 8 - ATA/ATAPI Command Set
+ * (ATA8-ACS)".
+ *
+ * If the SCT Command Transport feature set is not available, drive temperatures
+ * may be readable through SMART attributes. Since SMART attributes are not well
+ * defined, this method is only used as fallback mechanism.
+ *
+ * There are three SMART attributes which may report drive temperatures.
+ * Those are defined as follows (from
+ * http://www.cropel.com/library/smart-attribute-list.aspx).
+ *
+ * 190	Temperature	Temperature, monitored by a sensor somewhere inside
+ *			the drive. Raw value typicaly holds the actual
+ *			temperature (hexadecimal) in its rightmost two digits.
+ *
+ * 194	Temperature	Temperature, monitored by a sensor somewhere inside
+ *			the drive. Raw value typicaly holds the actual
+ *			temperature (hexadecimal) in its rightmost two digits.
+ *
+ * 231	Temperature	Temperature, monitored by a sensor somewhere inside
+ *			the drive. Raw value typicaly holds the actual
+ *			temperature (hexadecimal) in its rightmost two digits.
+ *
+ * Wikipedia defines attributes a bit differently.
+ *
+ * 190	Temperature	Value is equal to (100-temp. °C), allowing manufacturer
+ *	Difference or	to set a minimum threshold which corresponds to a
+ *	Airflow		maximum temperature. This also follows the convention of
+ *	Temperature	100 being a best-case value and lower values being
+ *			undesirable. However, some older drives may instead
+ *			report raw Temperature (identical to 0xC2) or
+ *			Temperature minus 50 here.
+ * 194	Temperature or	Indicates the device temperature, if the appropriate
+ *	Temperature	sensor is fitted. Lowest byte of the raw value contains
+ *	Celsius		the exact temperature value (Celsius degrees).
+ * 231	Life Left	Indicates the approximate SSD life left, in terms of
+ *	(SSDs) or	program/erase cycles or available reserved blocks.
+ *	Temperature	A normalized value of 100 represents a new drive, with
+ *			a threshold value at 10 indicating a need for
+ *			replacement. A value of 0 may mean that the drive is
+ *			operating in read-only mode to allow data recovery.
+ *			Previously (pre-2010) occasionally used for Drive
+ *			Temperature (more typically reported at 0xC2).
+ *
+ * Common denominator is that the first raw byte reports the temperature
+ * in degrees C on almost all drives. Some drives may report a fractional
+ * temperature in the second raw byte.
+ *
+ * Known exceptions (from libatasmart):
+ * - SAMSUNG SV0412H and SAMSUNG SV1204H) report the temperature in 10th
+ *   degrees C in the first two raw bytes.
+ * - A few Maxtor drives report an unknown or bad value in attribute 194.
+ * - Certain Apple SSD drives report an unknown value in attribute 190.
+ *   Only certain firmware versions are affected.
+ *
+ * Those exceptions affect older ATA drives and are currently ignored.
+ * Also, the second raw byte (possibly reporting the fractional temperature)
+ * is currently ignored.
+ *
+ * Many drives also report temperature limits in additional SMART data raw
+ * bytes. The format of those is not well defined and varies widely.
+ * The driver does not currently attempt to report those limits.
+ *
+ * According to data in smartmontools, attribute 231 is rarely used to report
+ * drive temperatures. At the same time, several drives report SSD life left
+ * in attribute 231, but do not support temperature sensors. For this reason,
+ * attribute 231 is currently ignored.
+ *
+ * Following above definitions, temperatures are reported as follows.
+ *   If SCT Command Transport is supported, it is used to read the
+ *   temperature and, if available, temperature limits.
+ * - Otherwise, if SMART attribute 194 is supported, it is used to read
+ *   the temperature.
+ * - Otherwise, if SMART attribute 190 is supported, it is used to read
+ *   the temperature.
+ */
+
+#include <linux/ata.h>
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/hwmon.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_device.h>
+#include <scsi/scsi_driver.h>
+#include <scsi/scsi_proto.h>
+
+struct drivetemp_data {
+	struct list_head list;		/* list of instantiated devices */
+	struct mutex lock;		/* protect data buffer accesses */
+	struct scsi_device *sdev;	/* SCSI device */
+	struct device *dev;		/* instantiating device */
+	struct device *hwdev;		/* hardware monitoring device */
+	u8 smartdata[ATA_SECT_SIZE];	/* local buffer */
+	int (*get_temp)(struct drivetemp_data *st, u32 attr, long *val);
+	bool have_temp_lowest;		/* lowest temp in SCT status */
+	bool have_temp_highest;		/* highest temp in SCT status */
+	bool have_temp_min;		/* have min temp */
+	bool have_temp_max;		/* have max temp */
+	bool have_temp_lcrit;		/* have lower critical limit */
+	bool have_temp_crit;		/* have critical limit */
+	int temp_min;			/* min temp */
+	int temp_max;			/* max temp */
+	int temp_lcrit;			/* lower critical limit */
+	int temp_crit;			/* critical limit */
+};
+
+static LIST_HEAD(drivetemp_devlist);
+
+#define ATA_MAX_SMART_ATTRS	30
+#define SMART_TEMP_PROP_190	190
+#define SMART_TEMP_PROP_194	194
+
+#define SCT_STATUS_REQ_ADDR	0xe0
+#define  SCT_STATUS_VERSION_LOW		0	/* log byte offsets */
+#define  SCT_STATUS_VERSION_HIGH	1
+#define  SCT_STATUS_TEMP		200
+#define  SCT_STATUS_TEMP_LOWEST		201
+#define  SCT_STATUS_TEMP_HIGHEST	202
+#define SCT_READ_LOG_ADDR	0xe1
+#define  SMART_READ_LOG			0xd5
+#define  SMART_WRITE_LOG		0xd6
+
+#define INVALID_TEMP		0x80
+
+#define temp_is_valid(temp)	((temp) != INVALID_TEMP)
+#define temp_from_sct(temp)	(((s8)(temp)) * 1000)
+
+static inline bool ata_id_smart_supported(u16 *id)
+{
+	return id[ATA_ID_COMMAND_SET_1] & BIT(0);
+}
+
+static inline bool ata_id_smart_enabled(u16 *id)
+{
+	return id[ATA_ID_CFS_ENABLE_1] & BIT(0);
+}
+
+static int drivetemp_scsi_command(struct drivetemp_data *st,
+				 u8 ata_command, u8 feature,
+				 u8 lba_low, u8 lba_mid, u8 lba_high)
+{
+	u8 scsi_cmd[MAX_COMMAND_SIZE];
+	int data_dir;
+
+	memset(scsi_cmd, 0, sizeof(scsi_cmd));
+	scsi_cmd[0] = ATA_16;
+	if (ata_command == ATA_CMD_SMART && feature == SMART_WRITE_LOG) {
+		scsi_cmd[1] = (5 << 1);	/* PIO Data-out */
+		/*
+		 * No off.line or cc, write to dev, block count in sector count
+		 * field.
+		 */
+		scsi_cmd[2] = 0x06;
+		data_dir = DMA_TO_DEVICE;
+	} else {
+		scsi_cmd[1] = (4 << 1);	/* PIO Data-in */
+		/*
+		 * No off.line or cc, read from dev, block count in sector count
+		 * field.
+		 */
+		scsi_cmd[2] = 0x0e;
+		data_dir = DMA_FROM_DEVICE;
+	}
+	scsi_cmd[4] = feature;
+	scsi_cmd[6] = 1;	/* 1 sector */
+	scsi_cmd[8] = lba_low;
+	scsi_cmd[10] = lba_mid;
+	scsi_cmd[12] = lba_high;
+	scsi_cmd[14] = ata_command;
+
+	return scsi_execute_req(st->sdev, scsi_cmd, data_dir,
+				st->smartdata, ATA_SECT_SIZE, NULL, HZ, 5,
+				NULL);
+}
+
+static int drivetemp_ata_command(struct drivetemp_data *st, u8 feature,
+				 u8 select)
+{
+	return drivetemp_scsi_command(st, ATA_CMD_SMART, feature, select,
+				     ATA_SMART_LBAM_PASS, ATA_SMART_LBAH_PASS);
+}
+
+static int drivetemp_get_smarttemp(struct drivetemp_data *st, u32 attr,
+				  long *temp)
+{
+	u8 *buf = st->smartdata;
+	bool have_temp = false;
+	u8 temp_raw;
+	u8 csum;
+	int err;
+	int i;
+
+	err = drivetemp_ata_command(st, ATA_SMART_READ_VALUES, 0);
+	if (err)
+		return err;
+
+	/* Checksum the read value table */
+	csum = 0;
+	for (i = 0; i < ATA_SECT_SIZE; i++)
+		csum += buf[i];
+	if (csum) {
+		dev_dbg(&st->sdev->sdev_gendev,
+			"checksum error reading SMART values\n");
+		return -EIO;
+	}
+
+	for (i = 0; i < ATA_MAX_SMART_ATTRS; i++) {
+		u8 *attr = buf + i * 12;
+		int id = attr[2];
+
+		if (!id)
+			continue;
+
+		if (id == SMART_TEMP_PROP_190) {
+			temp_raw = attr[7];
+			have_temp = true;
+		}
+		if (id == SMART_TEMP_PROP_194) {
+			temp_raw = attr[7];
+			have_temp = true;
+			break;
+		}
+	}
+
+	if (have_temp) {
+		*temp = temp_raw * 1000;
+		return 0;
+	}
+
+	return -ENXIO;
+}
+
+static int drivetemp_get_scttemp(struct drivetemp_data *st, u32 attr, long *val)
+{
+	u8 *buf = st->smartdata;
+	int err;
+
+	err = drivetemp_ata_command(st, SMART_READ_LOG, SCT_STATUS_REQ_ADDR);
+	if (err)
+		return err;
+	switch (attr) {
+	case hwmon_temp_input:
+		*val = temp_from_sct(buf[SCT_STATUS_TEMP]);
+		break;
+	case hwmon_temp_lowest:
+		*val = temp_from_sct(buf[SCT_STATUS_TEMP_LOWEST]);
+		break;
+	case hwmon_temp_highest:
+		*val = temp_from_sct(buf[SCT_STATUS_TEMP_HIGHEST]);
+		break;
+	default:
+		err = -EINVAL;
+		break;
+	}
+	return err;
+}
+
+static int drivetemp_identify_sata(struct drivetemp_data *st)
+{
+	struct scsi_device *sdev = st->sdev;
+	u8 *buf = st->smartdata;
+	struct scsi_vpd *vpd;
+	bool is_ata, is_sata;
+	bool have_sct_data_table;
+	bool have_sct_temp;
+	bool have_smart;
+	bool have_sct;
+	u16 *ata_id;
+	u16 version;
+	long temp;
+	int err;
+
+	/* SCSI-ATA Translation present? */
+	rcu_read_lock();
+	vpd = rcu_dereference(sdev->vpd_pg89);
+
+	/*
+	 * Verify that ATA IDENTIFY DEVICE data is included in ATA Information
+	 * VPD and that the drive implements the SATA protocol.
+	 */
+	if (!vpd || vpd->len < 572 || vpd->data[56] != ATA_CMD_ID_ATA ||
+	    vpd->data[36] != 0x34) {
+		rcu_read_unlock();
+		return -ENODEV;
+	}
+	ata_id = (u16 *)&vpd->data[60];
+	is_ata = ata_id_is_ata(ata_id);
+	is_sata = ata_id_is_sata(ata_id);
+	have_sct = ata_id_sct_supported(ata_id);
+	have_sct_data_table = ata_id_sct_data_tables(ata_id);
+	have_smart = ata_id_smart_supported(ata_id) &&
+				ata_id_smart_enabled(ata_id);
+
+	rcu_read_unlock();
+
+	/* bail out if this is not a SATA device */
+	if (!is_ata || !is_sata)
+		return -ENODEV;
+	if (!have_sct)
+		goto skip_sct;
+
+	err = drivetemp_ata_command(st, SMART_READ_LOG, SCT_STATUS_REQ_ADDR);
+	if (err)
+		goto skip_sct;
+
+	version = (buf[SCT_STATUS_VERSION_HIGH] << 8) |
+		  buf[SCT_STATUS_VERSION_LOW];
+	if (version != 2 && version != 3)
+		goto skip_sct;
+
+	have_sct_temp = temp_is_valid(buf[SCT_STATUS_TEMP]);
+	if (!have_sct_temp)
+		goto skip_sct;
+
+	st->have_temp_lowest = temp_is_valid(buf[SCT_STATUS_TEMP_LOWEST]);
+	st->have_temp_highest = temp_is_valid(buf[SCT_STATUS_TEMP_HIGHEST]);
+
+	if (!have_sct_data_table)
+		goto skip_sct;
+
+	/* Request and read temperature history table */
+	memset(buf, '\0', sizeof(st->smartdata));
+	buf[0] = 5;	/* data table command */
+	buf[2] = 1;	/* read table */
+	buf[4] = 2;	/* temperature history table */
+
+	err = drivetemp_ata_command(st, SMART_WRITE_LOG, SCT_STATUS_REQ_ADDR);
+	if (err)
+		goto skip_sct_data;
+
+	err = drivetemp_ata_command(st, SMART_READ_LOG, SCT_READ_LOG_ADDR);
+	if (err)
+		goto skip_sct_data;
+
+	/*
+	 * Temperature limits per AT Attachment 8 -
+	 * ATA/ATAPI Command Set (ATA8-ACS)
+	 */
+	st->have_temp_max = temp_is_valid(buf[6]);
+	st->have_temp_crit = temp_is_valid(buf[7]);
+	st->have_temp_min = temp_is_valid(buf[8]);
+	st->have_temp_lcrit = temp_is_valid(buf[9]);
+
+	st->temp_max = temp_from_sct(buf[6]);
+	st->temp_crit = temp_from_sct(buf[7]);
+	st->temp_min = temp_from_sct(buf[8]);
+	st->temp_lcrit = temp_from_sct(buf[9]);
+
+skip_sct_data:
+	if (have_sct_temp) {
+		st->get_temp = drivetemp_get_scttemp;
+		return 0;
+	}
+skip_sct:
+	if (!have_smart)
+		return -ENODEV;
+	st->get_temp = drivetemp_get_smarttemp;
+	return drivetemp_get_smarttemp(st, hwmon_temp_input, &temp);
+}
+
+static int drivetemp_identify(struct drivetemp_data *st)
+{
+	struct scsi_device *sdev = st->sdev;
+
+	/* Bail out immediately if there is no inquiry data */
+	if (!sdev->inquiry || sdev->inquiry_len < 16)
+		return -ENODEV;
+
+	/* Disk device? */
+	if (sdev->type != TYPE_DISK && sdev->type != TYPE_ZBC)
+		return -ENODEV;
+
+	return drivetemp_identify_sata(st);
+}
+
+static int drivetemp_read(struct device *dev, enum hwmon_sensor_types type,
+			 u32 attr, int channel, long *val)
+{
+	struct drivetemp_data *st = dev_get_drvdata(dev);
+	int err = 0;
+
+	if (type != hwmon_temp)
+		return -EINVAL;
+
+	switch (attr) {
+	case hwmon_temp_input:
+	case hwmon_temp_lowest:
+	case hwmon_temp_highest:
+		mutex_lock(&st->lock);
+		err = st->get_temp(st, attr, val);
+		mutex_unlock(&st->lock);
+		break;
+	case hwmon_temp_lcrit:
+		*val = st->temp_lcrit;
+		break;
+	case hwmon_temp_min:
+		*val = st->temp_min;
+		break;
+	case hwmon_temp_max:
+		*val = st->temp_max;
+		break;
+	case hwmon_temp_crit:
+		*val = st->temp_crit;
+		break;
+	default:
+		err = -EINVAL;
+		break;
+	}
+	return err;
+}
+
+static umode_t drivetemp_is_visible(const void *data,
+				   enum hwmon_sensor_types type,
+				   u32 attr, int channel)
+{
+	const struct drivetemp_data *st = data;
+
+	switch (type) {
+	case hwmon_temp:
+		switch (attr) {
+		case hwmon_temp_input:
+			return 0444;
+		case hwmon_temp_lowest:
+			if (st->have_temp_lowest)
+				return 0444;
+			break;
+		case hwmon_temp_highest:
+			if (st->have_temp_highest)
+				return 0444;
+			break;
+		case hwmon_temp_min:
+			if (st->have_temp_min)
+				return 0444;
+			break;
+		case hwmon_temp_max:
+			if (st->have_temp_max)
+				return 0444;
+			break;
+		case hwmon_temp_lcrit:
+			if (st->have_temp_lcrit)
+				return 0444;
+			break;
+		case hwmon_temp_crit:
+			if (st->have_temp_crit)
+				return 0444;
+			break;
+		default:
+			break;
+		}
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+static const struct hwmon_channel_info *drivetemp_info[] = {
+	HWMON_CHANNEL_INFO(chip,
+			   HWMON_C_REGISTER_TZ),
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT |
+			   HWMON_T_LOWEST | HWMON_T_HIGHEST |
+			   HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_LCRIT | HWMON_T_CRIT),
+	NULL
+};
+
+static const struct hwmon_ops drivetemp_ops = {
+	.is_visible = drivetemp_is_visible,
+	.read = drivetemp_read,
+};
+
+static const struct hwmon_chip_info drivetemp_chip_info = {
+	.ops = &drivetemp_ops,
+	.info = drivetemp_info,
+};
+
+/*
+ * The device argument points to sdev->sdev_dev. Its parent is
+ * sdev->sdev_gendev, which we can use to get the scsi_device pointer.
+ */
+static int drivetemp_add(struct device *dev, struct class_interface *intf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev->parent);
+	struct drivetemp_data *st;
+	int err;
+
+	st = kzalloc(sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return -ENOMEM;
+
+	st->sdev = sdev;
+	st->dev = dev;
+	mutex_init(&st->lock);
+
+	if (drivetemp_identify(st)) {
+		err = -ENODEV;
+		goto abort;
+	}
+
+	st->hwdev = hwmon_device_register_with_info(dev->parent, "drivetemp",
+						    st, &drivetemp_chip_info,
+						    NULL);
+	if (IS_ERR(st->hwdev)) {
+		err = PTR_ERR(st->hwdev);
+		goto abort;
+	}
+
+	list_add(&st->list, &drivetemp_devlist);
+	return 0;
+
+abort:
+	kfree(st);
+	return err;
+}
+
+static void drivetemp_remove(struct device *dev, struct class_interface *intf)
+{
+	struct drivetemp_data *st, *tmp;
+
+	list_for_each_entry_safe(st, tmp, &drivetemp_devlist, list) {
+		if (st->dev == dev) {
+			list_del(&st->list);
+			hwmon_device_unregister(st->hwdev);
+			kfree(st);
+			break;
+		}
+	}
+}
+
+static struct class_interface drivetemp_interface = {
+	.add_dev = drivetemp_add,
+	.remove_dev = drivetemp_remove,
+};
+
+static int __init drivetemp_init(void)
+{
+	return scsi_register_interface(&drivetemp_interface);
+}
+
+static void __exit drivetemp_exit(void)
+{
+	scsi_unregister_interface(&drivetemp_interface);
+}
+
+module_init(drivetemp_init);
+module_exit(drivetemp_exit);
+
+MODULE_AUTHOR("Guenter Roeck <linus@roeck-us.net>");
+MODULE_DESCRIPTION("Hard drive temperature monitor");
+MODULE_LICENSE("GPL");