hwmon: (hp-wmi-sensors) Fix failure to load on EliteDesk 800 G6

The EliteDesk 800 G6 stores a raw WMI string within the ACPI object in its
BIOS corresponding to one instance of HPBIOS_PlatformEvents.Name. This is
evidently a valid way of representing a WMI data item as far as the
Microsoft ACPI-WMI mapper is concerned, but is preventing the driver from
loading.

This seems quite rare, but add support for such strings. Treating this as a
quirk pretty much means adding that support anyway.

Also clean up an oversight in update_numeric_sensor_from_wobj() in which
the result of hp_wmi_strdup() was being used without error checking.

Reported-by: Lukasz Stelmach <l.stelmach@samsung.com>
Closes: https://lore.kernel.org/linux-hwmon/7850a0bd-60e7-88f8-1d6c-0bb0e3234fdc@roeck-us.net/
Tested-by: Lukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20231123054918.157098-1-james@equiv.tech
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

hwmon: (hp-wmi-sensors) Initialize pevents in hp_wmi_sensors_init()

The following warning is given by the Smatch static checker:

drivers/hwmon/hp-wmi-sensors.c:1937 hp_wmi_sensors_init()
error: uninitialized symbol 'pevents'.

If there are no instances of the HPBIOS_PlatformEvents WMI object
available, init_platform_events() never initializes this pointer,
which may then be passed to hp_wmi_debugfs_init() uninitialized.

The impact should be limited because hp_wmi_debugfs_init() uses this
pointer only if the count of HPBIOS_PlatformEvents instances is _not_
zero, while conversely, it will be uninitialized only if the count of
such instances _is_ zero. However, passing it uninitialized still
constitutes a bug.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/linux-hwmon/f72c129b-8c57-406a-bf41-bd889b65ea0f@moroto.mountain/
Signed-off-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20230725094817.588640-1-james@equiv.tech
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

hwmon: (hp-wmi-sensors) Get WMI instance count from WMI driver core

Commit 2a2b13ae50cf ("platform/x86: wmi: Allow retrieving the number of
WMI object instances") means we no longer need to find this ourselves.

Signed-off-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20230722172513.9324-2-james@equiv.tech
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

hwmon: (hp-wmi-sensors) fix debugfs check

Checking for Kconfig symbols with #if is wrong:

drivers/hwmon/hp-wmi-sensors.c:1141:5: error: "CONFIG_DEBUG_FS" is not defined, evaluates to 0 [-Werror=undef]

This could be an #ifdef, but an IS_ENABLED() check is even better to
give the best compile coverage.

Fixes: 23902f98f8d4 ("hwmon: add HP WMI Sensors driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20230601213216.3220550-1-arnd@kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

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>