hwmon: add HP WMI Sensors driver

Hewlett-Packard (and some HP Compaq) business-class computers report
hardware monitoring information via WMI. This driver exposes that
information to hwmon.

Initial support is provided for temperature, fan speed, and intrusion
sensor types. Provisional support is provided for voltage and current
sensor types.

HP's WMI implementation permits many other types of numeric sensors.
Therefore, a debugfs interface is also provided to enumerate and
inspect all numeric sensors visible on the WMI side. This should
facilitate adding support for other sensor types in the future.

Tested on a HP Z420, a HP EliteOne 800 G1, and a HP Compaq Elite 8300
SFF.

Note that provisionally supported sensor types are untested and seem
to be rare-to-nonexistent in the wild, having been encountered
neither on test systems nor in ACPI dumps from the Linux Hardware
Database. They are included because their popularity in general makes
their presence on past or future HP systems plausible and because no
doubt exists as to how the sensors themselves would be represented in
WMI (alarm attributes will need to wait for hardware to be located).
A 2005 HP whitepaper gives the relevant sensor object MOF definition
and sensor value scaling calculation, and both this driver and the
official HP Performance Advisor utility comply with them (confirmed
in the latter case by reverse engineering).

Link: https://h20331.www2.hp.com/hpsub/downloads/cmi_whitepaper.pdf
Signed-off-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20230522115645.509701-1-james@equiv.tech
[groeck: Set error return value for intrusion writes to -EINVAL.
	 Always accept writes of 0 even if there was no intrusion. ]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 12 insertions, 0 deletions

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index c52e44a393e9..307477b8a371 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -2421,6 +2421,18 @@ config SENSORS_ASUS_EC
 	  This driver can also be built as a module. If so, the module
 	  will be called asus_ec_sensors.
 
+config SENSORS_HP_WMI
+	tristate "HP WMI Sensors"
+	depends on ACPI_WMI
+	help
+	  If you say yes here you get support for the ACPI hardware monitoring
+	  interface found in HP (and some HP Compaq) business-class computers.
+	  Available sensors vary between systems. Temperature and fan speed
+	  sensors are the most common.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called hp_wmi_sensors.
+
 endif # ACPI
 
 endif # HWMON