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Subject[PATCH v9 2/8] Updated documentation
Date
From: Richard Neumann <mail@richard-neumann.de>

Updated documentation of the AMD Sensor Fusion Hub.

Signed-off-by: Richard Neumann <mail@richard-neumann.de>
---
Documentation/hid/amd-sfh-hid.rst | 275 ++++++++++++++----------------
1 file changed, 131 insertions(+), 144 deletions(-)

diff --git a/Documentation/hid/amd-sfh-hid.rst b/Documentation/hid/amd-sfh-hid.rst
index 1f2fe29ccd4f..d68ba2b85d1e 100644
--- a/Documentation/hid/amd-sfh-hid.rst
+++ b/Documentation/hid/amd-sfh-hid.rst
@@ -1,145 +1,132 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-
-AMD Sensor Fusion Hub
-=====================
-AMD Sensor Fusion Hub (SFH) is part of an 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 the kernel driver.
-
-1. Block Diagram
-================
-
-::
-
- ---------------------------------
- | HID User Space Applications |
- - -------------------------------
-
- ---------------------------------------------
- ---------------------------------
- | HID Core |
- ---------------------------------
-
- ---------------------------------
- | AMD HID Transport |
- ---------------------------------
-
- --------------------------------
- | AMD HID Client |
- | with HID Report Generator|
- --------------------------------
-
- --------------------------------
- | AMD MP2 PCIe Driver |
- --------------------------------
- OS
- ---------------------------------------------
- Hardware + Firmware
- --------------------------------
- | 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. Here: MP2 which is an ARM core connected to x86 for processing
-sensor data. The layer, which binds each device (AMD SFH HID driver) identifies the device type and
-registers with the hid core. Transport layer 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 layer implements the synchronous calls.
-
-AMD HID Client Layer
+========================================
+Kernel drivers: amd-sfh-pci, amd-sfh-hid
+========================================
+
+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>
+
+Description
+===========
+The AMD Sensor Fushion Hub (SFH) is part of a SOC on Ryzen-based platforms.
+The SFH uses HID over PCIe bus. In terms of architecture it is much more
+resmebles like ISH. However the major difference is, that currently HID reports
+are being generated within the kernel driver.
+
+Block Diagram
+-------------
+.. code-block:: none
+
+ +-------------------------------+
+ | HID User Space Applications |
+ +-------------------------------+
+ =================================
+ +-------------------------------+
+ | HID low-level driver |
+ | with HID report generator |
+ +-------------------------------+
+
+ +-------------------------------+
+ | HID platform driver |
+ +-------------------------------+
+
+ +-------------------------------+
+ | AMD SFH PCIe driver |
+ +-------------------------------+
+ =================================
+ +-------------------------------+
+ | SFH MP2 Processor |
+ +-------------------------------+
+
+HID low-level driver
--------------------
-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 complex as it is
-interface between MP2 PCIe layer and HID. HID client layer initialized the MP2 PCIe layer and holds
-the instance of MP2 layer. It identifies the number of sensors connected using MP2-PCIe layer. Base
-on that allocates the DRAM address for each and every sensor and pass it to MP2-PCIe driver.On
-enumeration of each the sensor, client layer fills the HID Descriptor structure and HID input repor
-structure. HID Feature report structure is optional. The report descriptor structure varies from
-sensor to sensor.
-
-AMD MP2 PCIe layer
-------------------
-MP2 PCIe Layer is responsible for making all transactions with the firmware over PCIe.
-The connection establishment between firmware and PCIe happens here.
-
-The communication between X86 and MP2 is split into three parts.
-1. Command transfer via the C2P mailbox registers.
-2. Data transfer via DRAM.
-3. Supported sensor info via P2C registers.
-
-Commands are sent to MP2 using C2P Mailbox registers. Writing into C2P Message registers generate
-interrupt to MP2. The client layer allocates the physical memory and the same is sent to MP2 via
-the PCI layer. MP2 firmware writes the command output to the access DRAM memory which the client
-layer has allocated. Firmware always writes minimum of 32 bytes into DRAM. So as a protocol driver
-shall allocate minimum of 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
-------------------------------------------------
-
-::
-
- | | | | |
- | | | | |
- | | | | |
- | | | | |
- | | | | |
- |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| | | | |
- <-------| | | | |
+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.
+
+HID platform driver (`amd-sfh-hid`)
+-----------------------------------
+The aforementioned HID devices are being managed, i.e. created on probing and
+destroyed on removing, by the platform driver. It is being loaded through ACPI
+table matching if the PCI driver was loaded successfully.
+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.
+On some systems the firmware does not provide the information about sensors
+connected to the SFH device. In this case, the detected sensors can be manually
+overridden by setting the driver's module parameter `sensor_mask=<int>`.
+
+PCI device driver (`amd-sfh-pci`)
+---------------------------------
+The PCI driver is responsible for making all transaction with the chip's
+firmware over PCI-e.
+The sensors are being 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 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.
+
+Driver loading
+--------------
+
++------------+-----------------+----------------------+
+| PCI driver | Platform driver | HID low-level driver |
++============+=================+======================+
+| Loaded at boot time if | Used by spawned HIDs |
+| device is present. | |
++------------------------------+----------------------+
+
+Data flow table
+---------------
+.. code-block:: none
+
+ +===============================================+
+ +============+ Get sensor mask | Platform driver |
+ | PCI driver | <---------------------------- +===============================================+
+ +============+ of available HID devices | * Probe HID devices according to sensor mask. |
+ ^ | * Start periodical polling from DRAM. |
+ | +-----------------------------------------------+
+ Start / stop sensor on |
+ respective HID requsts. |
+ | +==============================+ |
+ | | HID ll-driver | |
+ +--------------- +==============================+ <-----------+
+ | Provide reports as requested |
+ | by hid-code. |
+ +------------------------------+
+
+Quirks
+------
+On some systems, the sensor hub has not been programmed with information about
+the sensors active on the device. This results in no sensors bein activated and
+no HID devices being spawned by the driver. To manually active the respective
+sensors, you can load the module `amd-sfh-hid` with the kernel parameter
+`sensor_mask=<int>`. The available sensors are currently:
+
++----------------------+----------+
+| sensor | mask |
++======================+==========+
+| accelerometer | BIT(0) |
+| gyroscope | BIT(1) |
+| magnetometer | BIT(2) |
+| ambient light sensor | BIT(19) |
++----------------------+----------+
+
+To enable e.g. only the accelerometer:
+
+ $ cat /etc/modprobe.d/amd_sfh.conf
+ options amd_sfh_hid sensor_mask=1
--
2.30.0
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