[RFC,v2,20/20] fwctl/cxl: Add documentation to FWCTL CXL

Commit Message

Dave Jiang Nov. 15, 2024, 9:25 p.m. UTC

Add policy and operational documentation for FWCTL CXL.

Signed-off-by: Dave Jiang <[e-mail]>
---
 .../userspace-api/fwctl/fwctl-cxl.rst         | 91 +++++++++++++++++++
 Documentation/userspace-api/fwctl/index.rst   |  1 +
 2 files changed, 92 insertions(+)
 create mode 100644 Documentation/userspace-api/fwctl/fwctl-cxl.rst

Patch

diff --git a/Documentation/userspace-api/fwctl/fwctl-cxl.rst b/Documentation/userspace-api/fwctl/fwctl-cxl.rst
new file mode 100644
index 000000000000..158e9aa45609
--- /dev/null
+++ b/Documentation/userspace-api/fwctl/fwctl-cxl.rst
@@ -0,0 +1,91 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+================
+fwctl cxl driver
+================
+
+:Author: Dave Jiang
+
+Overview
+========
+
+The CXL spec defines a set of commands that can be issued to the mailbox of a
+CXL device or switch. It also left room for vendor specific commands to be
+issued to the mailbox as well. fwctl provides a path to issue a set of allowed
+mailbox commands from user space to the device moderated by the kernel driver.
+
+While there are a large set of mailbox commands, only the feature related
+commands will be allowed to be issued through fwctl initially. No background
+commands will be supported at this time.
+
+CXL spec r3.1 8.2.9.6.1 Get Supported Features (Opcode 0500h)
+CXL spec r3.1 8.2.9.6.2 Get Feature (Opcode 0501h)
+CXL spec r3.1 8.2.9.6.3 Set Feature (Opcode 0502h)
+
+The "Get Supported Features" return data may be filtered by the kernel driver to
+drop any features that are forbidden by the kernel or being exclusively used by
+the kernel. The "Get Supported Featuers" command falls under the fwctl policy
+of FWCTL_RPC_CONFIGURATION.
+
+The "Get Features" commands falls under the policy FWCTL_RPC_DEBUG_READ_ONLY.
+
+For "Set Feature" command, the access policy currently is broken down into two
+categories depending on the set feature effects reported by the device. If the
+set feature will cause immediate change to the device, the fwctl access policy
+must be FWCTL_RPC_DEBUG_WRITE_FULL. The effects for this level are
+"immediate config change", "immediate data change", "immediate policy change",
+or "immediate log change" for the set effects mask. If the effects are "config
+change with cold reset" or "config change with conventional reset", then the
+fwctl access policy must be FWCTL_RPC_DEBUG_WRITE or higher.
+
+fwctl cxl User API
+==================
+
+.. kernel-doc:: include/uapi/fwctl/cxl.h
+
+1. Driver info query
+--------------------
+
+First step for the app is to issue the ioctl(FWCTL_CMD_INFO) in order to retrieve
+the information from the driver. A ``struct fwctl_info`` needs to be filled out
+with the ``fwctl_info.out_device_type`` set to ``FWCTL_DEVICE_TYPE_CXL``. The
+return data should be ``struct fwctl_info_cxl`` that contains the number of
+commands supported by the driver.
+
+2. Hardware command info query
+------------------------------
+
+Second step is to retrieve the command information from the driver. A ``struct
+fwctl_hw_info`` is sent with the ioctl(FWCTL_CMD_HW_INFO).
+``fwctl_hw_info.nr_cmds`` should be set to the number retrieved from the driver
+info query. A user buffer of ``struct fwctl_hw_info_out`` including an inlined
+array of ``struct fwctl_hw_info_out`` numbered of nr_cmds should be allocated and
+set as ``fwctl_hw_info.out_device_data``. For each command supported, its
+relevant information is returned such as the driver command id, the opcode it
+supports, the effect reported by the device if it's a write command, and its
+expected input and output sizes.
+
+3. Send hardware command
+------------------------
+
+Last step is to send hardware command to the driver from user space via
+ioctl(FWCTL_RPC). A ``struct fwctl_rpc_cxl`` should be pointed to by
+``fwctl_rpc.in``. ``struct fwctl_rpc_cxl.in_payload`` should point to
+the hardware input structure that is defined by the CXL spec. ``fwctl_rpc.out``
+points to the buffer that contains a ``struct fwctl_rpc_cxl_out`` that includes
+the hardware output data inlined as ``fwctl_rpc_cxl_out.payload``.
+
+For a get/set feature command, it is recommended to run the "get supported
+features" command first to retrieve the desired feature information first
+before sending a get or set feature command. For a "set feature" command,
+the retrieved info contains an effects field that details the resulting
+"set feature" command will trigger. That should inform the user whether
+the system is configured to allowed the "set feature" command or not.
+
+
+fwctl cxl Kernel API
+====================
+
+.. kernel-doc:: drivers/fwctl/cxl/cxl.c
+   :export:
+.. kernel-doc:: include/cxl/mailbox.h
diff --git a/Documentation/userspace-api/fwctl/index.rst b/Documentation/userspace-api/fwctl/index.rst
index 06959fbf1547..d9d40a468a31 100644
--- a/Documentation/userspace-api/fwctl/index.rst
+++ b/Documentation/userspace-api/fwctl/index.rst
@@ -10,3 +10,4 @@  to securely construct and execute RPCs inside device firmware.
    :maxdepth: 1
 
    fwctl
+   fwctl-cxl