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>

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
+=======================	=====================================================

Documentation/hwmon/index.rst

@@ -47,6 +47,7 @@ Hardware Monitoring Kernel Drivers
    da9055
    dell-smm-hwmon
    dme1737
+   drivetemp
    ds1621
    ds620
    emc1403

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

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