2020-11-03 18:30:49 +08:00
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.. SPDX-License-Identifier: GPL-2.0
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AMD Sensor Fusion Hub
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=====================
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2020-12-29 04:53:21 +08:00
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AMD Sensor Fusion Hub (SFH) is part of an SOC starting from Ryzen-based platforms.
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2020-11-03 18:30:49 +08:00
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The solution is working well on several OEM products. AMD SFH uses HID over PCIe bus.
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In terms of architecture it resembles ISH, however the major difference is all
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the HID reports are generated as part of the kernel driver.
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2020-12-29 04:53:21 +08:00
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Block Diagram
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2020-11-03 18:30:49 +08:00
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::
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---------------------------------
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| HID User Space Applications |
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- -------------------------------
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---------------------------------------------
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---------------------------------
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| HID Core |
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---------------------------------
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---------------------------------
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| AMD HID Transport |
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---------------------------------
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--------------------------------
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| AMD HID Client |
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| with HID Report Generator|
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--------------------------------
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--------------------------------
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| AMD MP2 PCIe Driver |
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--------------------------------
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OS
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---------------------------------------------
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Hardware + Firmware
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--------------------------------
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| SFH MP2 Processor |
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--------------------------------
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AMD HID Transport Layer
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-----------------------
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AMD SFH transport is also implemented as a bus. Each client application executing in the AMD MP2 is
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2020-12-29 04:53:21 +08:00
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registered as a device on this bus. Here, MP2 is an ARM core connected to x86 for processing
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2020-11-03 18:30:49 +08:00
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sensor data. The layer, which binds each device (AMD SFH HID driver) identifies the device type and
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registers with the HID core. Transport layer attaches a constant "struct hid_ll_driver" object with
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each device. Once a device is registered with HID core, the callbacks provided via this struct are
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used by HID core to communicate with the device. AMD HID Transport layer implements the synchronous calls.
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AMD HID Client Layer
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--------------------
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2020-12-29 04:53:21 +08:00
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This layer is responsible to implement HID requests and descriptors. As firmware is OS agnostic, HID
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client layer fills the HID request structure and descriptors. HID client layer is complex as it is
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2020-12-29 04:53:21 +08:00
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interface between MP2 PCIe layer and HID. HID client layer initializes the MP2 PCIe layer and holds
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the instance of MP2 layer. It identifies the number of sensors connected using MP2-PCIe layer. Based
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on that allocates the DRAM address for each and every sensor and passes it to MP2-PCIe driver. On
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enumeration of each sensor, client layer fills the HID Descriptor structure and HID input report
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2020-11-03 18:30:49 +08:00
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structure. HID Feature report structure is optional. The report descriptor structure varies from
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sensor to sensor.
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AMD MP2 PCIe layer
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------------------
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MP2 PCIe Layer is responsible for making all transactions with the firmware over PCIe.
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The connection establishment between firmware and PCIe happens here.
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The communication between X86 and MP2 is split into three parts.
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1. Command transfer via the C2P mailbox registers.
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2. Data transfer via DRAM.
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3. Supported sensor info via P2C registers.
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2020-12-29 04:53:21 +08:00
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Commands are sent to MP2 using C2P Mailbox registers. Writing into C2P Message registers generates
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interrupt to MP2. The client layer allocates the physical memory and the same is sent to MP2 via
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the PCI layer. MP2 firmware writes the command output to the access DRAM memory which the client
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layer has allocated. Firmware always writes minimum of 32 bytes into DRAM. So as a protocol driver
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shall allocate minimum of 32 bytes DRAM space.
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Enumeration and Probing flow
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----------------------------
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::
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HID AMD AMD AMD -PCIe MP2
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Core Transport Client layer layer FW
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| | | on Boot Driver Loaded |
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| | | MP2-PCIe Int |
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| | |---Get Number of sensors-> | |
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| | | Read P2C |
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| | | Register |
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| | | Loop(for No of Sensors) | |
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| | |----------------------| | |
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| | | Create HID Descriptor| | |
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| | | Create Input report | | |
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| | | Descriptor Map | | |
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| | | the MP2 FW Index to | | |
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| | | HID Index | | |
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| | | Allocate the DRAM | Enable |
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| | | address | Sensors |
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| | |----------------------| | |
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| | HID transport| | Enable |
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| |<--Probe------| |---Sensor CMD--> |
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| | Create the | | |
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| | HID device | | |
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| | (MFD) | | |
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| | by Populating| | |
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| | the HID | | |
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| | ll_driver | | |
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| HID | | | |
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| add | | | |
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|Device | | | |
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|<------------- | | | |
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Data Flow from Application to the AMD SFH Driver
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------------------------------------------------
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|HID_req | | | |
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|get_report | | | |
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|------------->| | | |
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| | HID_get_input| | |
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| | report | | |
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| |------------->|------------------------| | |
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| | | Read the DRAM data for| | |
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| | | requested sensor and | | |
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| | | create the HID input | | |
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| | | report | | |
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| | |------------------------| | |
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| |Data received | | |
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| | in HID report| | |
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To |<-------------|<-------------| | |
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Applications| | | | |
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<-------| | | | |
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