.. SPDX-License-Identifier: GPL-2.0
AMD Sensor Fusion Hub:-
======================
AMD sensor fushion Hub is part of a SOC starting from ryzon based platforms.
The solution is working well on windows OS in several
OEM products. AMD SFH uses HID over PCIe bus. In terms of architecture
it is much more resmebles like ISH .However the major diffrence is all
The hid reports are generated as part of kernel driver.
Block Diagram:-
=============
-------------------------------
| HID User Space Applications |
-------------------------------
---------------------------------------------
---------------------------------
| HID Core |
---------------------------------
---------------------------------
| AMD HID Transport Driver |
---------------------------------
--------------------------------
| AMD HID Client Driver |
| with HID Report Generator|
--------------------------------
--------------------------------
| AMD MP2 PCIe Driver |
--------------------------------
---------------------------------------------
-------------------------------
| SFH MP2 Processor |
--------------------------------
AMD HID Transport Layer :-
***************************
AMD SFH transport is also implemented as a bus. Each client application
executing in the AMD MP2 is registered as a device on this bus.
The driver, which binds each device (AMD SFH HID driver) identifies
the device type and registers with the hid core. Transport drivers
attach a constant "struct hid_ll_driver" object with each device.
Once a device is registered with HID core, the callbacks provided via
this struct are used by HID core to communicate with the device.
AMD HID Transport driver implements the synchronous calls.
AMD HID Client Driver:-
**********************
This driver is responsible to implement HID request and descriptors.
As firmware is OS agnostic, HID client driver fills the HID request
structure and descriptors. HID client driver is in complex in nature
as it is interface between MP2 PCIe driver and HID. HID client driver
initialized the MP2 PCIe driver and holds the instance of MP2 driver.
It identified the number of sensors connected using MP2- PCIe driver and
based on that allocate the DRAM address for each and every sensor and
pass it to MP2-PCIe driver.
On enumeration of each sensor, client driver fills out the HID Descriptor
structure and HID input report structure. HID Feature report structure can
be optional. The report descriptor structure varies sensor to sensor.
Now on enumeration client driver does two major things
1. Register the HID sensor client to virtual bus (Platform driver) and bind it.
2. Probes the AMD HID transport driver. Which in turns register device to the core.
AMD MP2 PCIe Driver:-
********************
MP2 PCIe driver is responsible for making all transaction with the firmware over
PCIe.The connection establishment between firmware and MP2 PCIe driver happens here.
The communication between X86 and MP2 is spilt into three parts.
1. Command Transfer => C2P Mailbox Register are used
2. Data Transfer => DRAM
Commands are sent to MP2 using C2P Mail Box registers. These C2P registers
are mapped in PCIe address space.Writing into C2P Message register generate
interrupt to MP2. The client driver allocates the physical memory and send
the same to MP2 for data transfer. MP2 firmware uses DRAM interface registers
to indirectly access DRAM memory. For Firmware always write minimum 32 bytes
into DRAM.So it is expected that driver shall allocate minimum 32 bytes DRAM space.
Enumeration and Probing flow:-
*****************************
HID AMD AMD AMD -PCIe MP2
Core Transport Client Driver Driver FW
| | | | |
| | on Boot Driver Loaded | |
| | | | |
| | |----MP2-PCIe Int---------> | |
| | | | |
| | |---Get Number of sensors-> | |
| | | Read P2C |
| | | Register |
| | | | |
| | | Loop(for No of Sensors) | |
| | |----------------------| | |
| | | Create HID Descriptor| | |
| | | Create Input report | | |
| | | Descriptor Map | | |
| | | the MP2 FW Index to | | |
| | | HID Index | | |
| | | Allocate the DRAM | Enable |
| | | address | Sensors |
| | |----------------------| | |
| | HID transport| | Enable |
| |<--Probe------| |---Sensor CMD--> |
| | Create the | | |
| | HID device | | |
| | (MFD) | | |
| | by Populating| | |
| | the HID | | |
| | ll_driver | | |
| HID | | | |
| add | | | |
|Device | | | |
|<------------- | | | |
Data Flow from Application to the AMD SFH Driver:-
*************************************************
| | | | |
Get | | | | |
Input | | | | |
Report | | | | |
---> | | | | |
|HID_req | | | |
|get_report | | | |
|------------->| | | |
| | HID_get_input| | |
| | report | | |
| |------------->|------------------------| | |
| | | Read the DRAM data for| | |
| | | requsted sensor and | | |
| | | create the HID input | | |
| | | report | | |
| | |------------------------| | |
| |Data received | | |
| | in HID report| | |
To |<-------------|<-------------| | |
Applications | | | |
<-------| | | | |
Data Flow from AMD SFH Driver to Application:-
**********************************************
| | | | |
| | |------------------------| | |
| | |Periodically Read | | |
| | |the data for all | | |
| | |enumerated sensors | | |
| | |from the dram and create| | |
| | | HID Input reports | | |
| | |------------------------| | |
| |HID Input | | |
| |Input report | | |
<----submit to Application-----| | |
| | | | |
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