platform/x86: dell: Add new dell-wmi-ddv driver

The dell-wmi-ddv driver adds support for reading
the current temperature and ePPID of ACPI batteries
on supported Dell machines.

Since the WMI interface used by this driver does not
do any input validation and thus cannot be used for probing,
the driver depends on the ACPI battery extension machanism
to discover batteries.

The driver also supports a debugfs interface for retrieving
buffers containing fan and thermal sensor information.
Since the meaing of the content of those buffers is currently
unknown, the interface is meant for reverse-engineering and
will likely be replaced with an hwmon interface once the
meaning has been understood.

The driver was tested on a Dell Inspiron 3505.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220927204521.601887-3-W_Armin@gmx.de
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Documentation/ABI/testing/debugfs-dell-wmi-ddv

@@ -0,0 +1,21 @@
+What:		/sys/kernel/debug/dell-wmi-ddv-<wmi_device_name>/fan_sensor_information
+Date:		September 2022
+KernelVersion:	6.1
+Contact:	Armin Wolf <W_Armin@gmx.de>
+Description:
+		This file contains the contents of the fan sensor information buffer,
+		which contains fan sensor entries and a terminating character (0xFF).
+
+		Each fan sensor entry consists of three bytes with an unknown meaning,
+		interested people may use this file for reverse-engineering.
+
+What:		/sys/kernel/debug/dell-wmi-ddv-<wmi_device_name>/thermal_sensor_information
+Date:		September 2022
+KernelVersion:	6.1
+Contact:	Armin Wolf <W_Armin@gmx.de>
+Description:
+		This file contains the contents of the thermal sensor information buffer,
+		which contains thermal sensor entries and a terminating character (0xFF).
+
+		Each thermal sensor entry consists of five bytes with an unknown meaning,
+		interested people may use this file for reverse-engineering.

Documentation/ABI/testing/sysfs-platform-dell-wmi-ddv

@@ -0,0 +1,7 @@
+What:		/sys/class/power_supply/<battery_name>/eppid
+Date:		September 2022
+KernelVersion:	6.1
+Contact:	Armin Wolf <W_Armin@gmx.de>
+Description:
+		Reports the Dell ePPID (electronic Dell Piece Part Identification)
+		of the ACPI battery.

MAINTAINERS

@@ -5851,6 +5851,13 @@ L:	Dell.Client.Kernel@dell.com
 S:	Maintained
 F:	drivers/platform/x86/dell/dell-wmi-descriptor.c
 
+DELL WMI DDV DRIVER
+M:	Armin Wolf <W_Armin@gmx.de>
+S:	Maintained
+F:	Documentation/ABI/testing/debugfs-dell-wmi-ddv
+F:	Documentation/ABI/testing/sysfs-platform-dell-wmi-ddv
+F:	drivers/platform/x86/dell/dell-wmi-ddv.c
+
 DELL WMI SYSMAN DRIVER
 M:	Divya Bharathi <divya.bharathi@dell.com>
 M:	Prasanth Ksr <prasanth.ksr@dell.com>

drivers/platform/x86/dell/Kconfig

@@ -189,6 +189,19 @@ config DELL_WMI_DESCRIPTOR
 	default n
 	depends on ACPI_WMI
 
+config DELL_WMI_DDV
+	tristate "Dell WMI sensors Support"
+	default m
+	depends on ACPI_BATTERY
+	depends on ACPI_WMI
+	help
+	  This option adds support for WMI-based sensors like
+	  battery temperature sensors found on some Dell notebooks.
+	  It also supports reading of the battery ePPID.
+
+	  To compile this drivers as a module, choose M here: the module will
+	  be called dell-wmi-ddv.
+
 config DELL_WMI_LED
 	tristate "External LED on Dell Business Netbooks"
 	default m

drivers/platform/x86/dell/Makefile

@@ -19,5 +19,6 @@ dell-wmi-objs				:= dell-wmi-base.o
 dell-wmi-$(CONFIG_DELL_WMI_PRIVACY)	+= dell-wmi-privacy.o
 obj-$(CONFIG_DELL_WMI_AIO)		+= dell-wmi-aio.o
 obj-$(CONFIG_DELL_WMI_DESCRIPTOR)	+= dell-wmi-descriptor.o
+obj-$(CONFIG_DELL_WMI_DDV)		+= dell-wmi-ddv.o
 obj-$(CONFIG_DELL_WMI_LED)		+= dell-wmi-led.o
 obj-$(CONFIG_DELL_WMI_SYSMAN)		+= dell-wmi-sysman/