Linux HWMON sensors driver for ASUS motherboards to read sensors from the embedded controller

Thanks to @0lvin efforts this driver was mainlined. Please use the in-kernel version or the enhanced one here.

Many ASUS motherboards do not publish all the available sensors via the Super I/O chip but some of them are available through the embedded controller (EC) registers.

This driver implements reading those sensor data via the WMI method BREC, which is known to be present in all ASUS motherboards based on the AMD 500 series chipsets (and probably is available in other models too). The driver needs to know exact register addresses for the sensors and thus support for each motherboard has to be added explicitly.

The EC registers do not provide critical values for the sensors and as such they are not published to the HWMON.

1. ROG CROSSHAIR VIII HERO
2. ROG CROSSHAIR VIII DARK HERO
3. ROG CROSSHAIR VIII FORMULA
4. ROG STRIX X570-E GAMING
5. ROG STRIX B550-E GAMING
6. Pro WS X570-ACE

First, you need to find out which EC registers to read (although) they are pretty typical. If you have no idea is there any, you can try the hwinfo software under Windows that will show the EC node and known sensors for it. When you have the data (or decided to probe the default set), the following changes to the source code need to be made:

1. Add your board name to the asus_wmi_ec_dmi_table array and a new enum value to the board enum. You can find the board name in /sys/class/dmi/id/board_name or using dmidecode.

2. Add new entry to the known_board_sensors array where list sensors for the board. If the board sensors span more than ASUS_WMI_BLOCK_READ_REGISTERS_MAX, a rewrite of the update_ec_sensors() will be required.

3. If you discover new sensors, modify the known_ec_sensor enum and add it to the known_ec_sensors array. For each sensor you need to provide its size in bytes (for example, RPM counters span two single-byte registers), its bank index and register index within the bank. If the sensor spans two or more registers, provide the first one (the smaller number).

Compile and it should work.