HID: SFH: Add documentation

Add Documentation/hid/amd-sfh-hid.rst file which was by mistake dropped by
me when applying the series.

Fixes: 302f0dad8c97a11ab ("SFH: Add maintainers and documentation for AMD SFH based on HID framework")
Reported-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Originally-by: Sandeep Singh <Sandeep.Singh@amd.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 145 insertions, 0 deletions

diff --git a/Documentation/hid/amd-sfh-hid.rst b/Documentation/hid/amd-sfh-hid.rst
new file mode 100644
index 000000000000..1f2fe29ccd4f
--- /dev/null
+++ b/Documentation/hid/amd-sfh-hid.rst
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+.. 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
+--------------------
+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|              |              |                           |                 |
+        <-------|              |              |                           |                 |