pds_fwctl: add Documentation entries

Add pds_fwctl to the driver and fwctl documentation pages.

Link: https://patch.msgid.link/r/[email protected]
Reviewed-by: Leon Romanovsky <[email protected]>
Signed-off-by: Shannon Nelson <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: emusln

Documentation/userspace-api/fwctl/fwctl.rst

@@ -150,6 +150,7 @@ fwctl User API
 
 .. kernel-doc:: include/uapi/fwctl/fwctl.h
 .. kernel-doc:: include/uapi/fwctl/mlx5.h
+.. kernel-doc:: include/uapi/fwctl/pds.h
 
 sysfs Class
 -----------

Documentation/userspace-api/fwctl/index.rst

@@ -11,3 +11,4 @@ to securely construct and execute RPCs inside device firmware.
 
    fwctl
    fwctl-cxl
+   pds_fwctl

Documentation/userspace-api/fwctl/pds_fwctl.rst

@@ -0,0 +1,46 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================
+fwctl pds driver
+================
+
+:Author: Shannon Nelson
+
+Overview
+========
+
+The PDS Core device makes a fwctl service available through an
+auxiliary_device named pds_core.fwctl.N.  The pds_fwctl driver binds to
+this device and registers itself with the fwctl subsystem.  The resulting
+userspace interface is used by an application that is a part of the
+AMD Pensando software package for the Distributed Service Card (DSC).
+
+The pds_fwctl driver has little knowledge of the firmware's internals.
+It only knows how to send commands through pds_core's message queue to the
+firmware for fwctl requests.  The set of fwctl operations available
+depends on the firmware in the DSC, and the userspace application
+version must match the firmware so that they can talk to each other.
+
+When a connection is created the pds_fwctl driver requests from the
+firmware a list of firmware object endpoints, and for each endpoint the
+driver requests a list of operations for that endpoint.
+
+Each operation description includes a firmware defined command attribute
+that maps to the FWCTL scope levels.  The driver translates those firmware
+values into the FWCTL scope values which can then be used for filtering the
+scoped user requests.
+
+pds_fwctl User API
+==================
+
+Each RPC request includes the target endpoint and the operation id, and in
+and out buffer lengths and pointers.  The driver verifies the existence
+of the requested endpoint and operations, then checks the request scope
+against the required scope of the operation.  The request is then put
+together with the request data and sent through pds_core's message queue
+to the firmware, and the results are returned to the caller.
+
+The RPC endpoints, operations, and buffer contents are defined by the
+particular firmware package in the device, which varies across the
+available product configurations.  The details are available in the
+specific product SDK documentation.