- Supported adapters:
- AMD Sensor Fusion Hub PCIe interface
Datasheet: not publicly available.
- Authors:
- Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
- Nehal Bakulchandra Shah <Nehal-bakulchandra.Shah@amd.com>
- Sandeep Singh <sandeep.singh@amd.com>
- Richard Neumann <mail@richard-neumann.de>
The AMD Sensor Fusion Hub (SFH) is part of a SOC on Ryzen-based platforms. The SFH uses HID over PCIe bus. In terms of architecture it resembles the ISH. However, the major difference is that currently HID reports are being generated within the kernel driver.
+-------------------------------+
| HID User Space Applications |
+-------------------------------+
=================================
+-------------------------------+
| HID low-level driver |
| with HID report generator |
+-------------------------------+
+-------------------------------+
| HID client interface |
+-------------------------------+
+-------------------------------+
| AMD SFH PCIe driver |
+-------------------------------+
=================================
+-------------------------------+
| SFH MP2 Processor |
+-------------------------------+
The driver is conceived in a multi-layer architecture. The level closest to the applications is the HID low-level (LL) driver, which implements the functions defined by the hid-core API to manage the respective HID devices and process reports. Therefor, the HID-LL-driver starts and stops the sensors as needed by invoking the exposed functions from the PCI driver (see below) and creates DMA mappings to access the DRAM of the PCI device to retrieve feature and input reports from it.
The aforementioned HID devices are being managed, i.e. created on probing and destroyed on removing, by the client interface used by the PCI driver. It determines the HID devices to be created on startup using the connected sensors bitmask retrieved by invoking the respective function of the PCI driver.
The PCI driver is responsible for making all transactions with the chip's firmware over PCI-e. The sensors are started and stopped respectively by writing commands and, where applicable, DRAM addresses to certain device registers. The sensor's input report data can then be accessed by accessing the DRAM through DMA-mapped virtual addresses. Commands are sent to the device using CPU to PCI (C2P) mail box registers. These C2P registers are mapped in PCIe address space. Writing into the device message registers generates interrupts. The device's firmware uses DRAM interface registers to indirectly access DRAM memory. It is recommended to always write a minimum of 32 bytes into the DRAM.
| PCI driver | HID low-level driver |
|---|---|
| Loaded at boot time if device is present. | Used by spawned HIDs |
+===============================================+
+============+ Get sensor mask | HID client |
| PCI driver | <---------------------------- +===============================================+
+============+ of available HID devices | * Probe HID devices according to sensor mask. |
^ | * Start periodic polling from DRAM. |
| +-----------------------------------------------+
Start / stop sensor on |
respective HID requests. |
| +==============================+ |
| | HID ll-driver | |
+--------------- +==============================+ <-----------+
| Provide reports as requested |
| by hid-code. |
+------------------------------+
On some systems, the sensor hub has not been programmed with information about the sensors available on the device. This would result in no sensors being activated and no HID devices being spawned by the driver. The driver already has quirks for some devices, that automatically compensate for this by DMI matching an appropriate sensor mask for the respective system. You can also activate the respective sensors manually, by loading the module amd-sfh with the kernel parameter sensor_mask=<int>. Available sensors are:
| sensor | index | mask |
|---|---|---|
| accelerometer | 0 | BIT(0) = 1 |
| gyroscope | 1 | BIT(1) = 2 |
| magnetometer | 2 | BIT(2) = 4 |
| ambient light sensor | 19 | BIT(19) = 524288 |
The values are additive, so to enable the gyroscope and the ambient light sensor, use a value of 524290.
$ cat /etc/modprobe.d/amd_sfh.conf
options amd_sfh sensor_mask=524290