new file mode 100644
@@ -0,0 +1,153 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+AMD Sensor Fusion Hub:-
+======================
+AMD Sensor Fusion Hub is part of a SOC starting from Ryzen based platforms.
+The solution is working well on several OEM products. AMD SFH uses HID over PCIe bus.
+In terms of architecture it resembles ISH .However the major difference is all
+The hid reports are generated as part of kernel driver.
+
+Block Diagram:-
+=============
+ -------------------------------
+ | HID User Space Applications |
+ -------------------------------
+---------------------------------------------
+ ---------------------------------
+ | HID Core |
+ ---------------------------------
+
+ ---------------------------------
+ | AMD HID Transport |
+ ---------------------------------
+
+ --------------------------------
+ | AMD HID Client |
+ | 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. MP2 which is an ARM® Cortex-M4 core based co-processor to
+x86. 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 synchronouscalls.
+
+AMD HID Client Layer:-
+**********************
+This layer is responsible to implement HID request and descriptors. As firmware is OS agnostic,
+HID client layer fills the HID request structure and descriptors. HID client layer is in complex
+in nature as it is interface between MP2 PCIe driver and HID. HID client layer 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 layer 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 layer 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 layer:-
+********************
+MP2 PCIe Layer is responsible for making all transaction with the firmware over PCIe.
+The connection establishment between firmware and PCIe 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
+3. Supported sensor info => P2C Register
+
+Commands are sent to MP2 using C2P Mail Box registers. These C2P registers are common between x86
+and MP2. Writing into C2P Message register generate interrupt to MP2. The client layer allocates
+the physical memory and send the same to MP2 for data transfer. MP2 firmware uses HUBIF interface
+to 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 layer layer 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| | |
+ | | | requested 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-----| | |
+ | | | | |
@@ -934,6 +934,14 @@ S: Supported
F: arch/arm64/boot/dts/amd/amd-seattle-xgbe*.dtsi
F: drivers/net/ethernet/amd/xgbe/
+AMD SENSOR FUSION HUB DRIVER
+M: Nehal Shah <nehal-bakulchandra.shah@amd.com>
+M: Sandeep Singh <sandeep.singh@amd.com>
+L: linux-input@vger.kernel.org
+S: Maintained
+F: Documentation/hid/amd-sfh*
+F: drivers/hid/amd-sfh-hid/
+
ANALOG DEVICES INC AD5686 DRIVER
M: Michael Hennerich <Michael.Hennerich@analog.com>
L: linux-pm@vger.kernel.org