1 files changed, 168 insertions, 0 deletions
diff --git a/Documentation/driver-api/mei/mei-client-bus.rst b/Documentation/driver-api/mei/mei-client-bus.rst
new file mode 100644
index 000000000000..f242b3f8d6aa
--- /dev/null
+++ b/Documentation/driver-api/mei/mei-client-bus.rst
@@ -0,0 +1,168 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============================================
+Intel(R) Management Engine (ME) Client bus API
+==============================================
+
+
+Rationale
+=========
+
+The MEI character device is useful for dedicated applications to send and receive
+data to the many FW appliance found in Intel's ME from the user space.
+However, for some of the ME functionalities it makes sense to leverage existing software
+stack and expose them through existing kernel subsystems.
+
+In order to plug seamlessly into the kernel device driver model we add kernel virtual
+bus abstraction on top of the MEI driver. This allows implementing Linux kernel drivers
+for the various MEI features as a stand alone entities found in their respective subsystem.
+Existing device drivers can even potentially be re-used by adding an MEI CL bus layer to
+the existing code.
+
+
+MEI CL bus API
+==============
+
+A driver implementation for an MEI Client is very similar to any other existing bus
+based device drivers. The driver registers itself as an MEI CL bus driver through
+the ``struct mei_cl_driver`` structure defined in :file:`include/linux/mei_cl_bus.c`
+
+.. code-block:: C
+
+        struct mei_cl_driver {
+                struct device_driver driver;
+                const char *name;
+
+                const struct mei_cl_device_id *id_table;
+
+                int (*probe)(struct mei_cl_device *dev, const struct mei_cl_id *id);
+                int (*remove)(struct mei_cl_device *dev);
+        };
+
+
+
+The mei_cl_device_id structure defined in :file:`include/linux/mod_devicetable.h` allows a
+driver to bind itself against a device name.
+
+.. code-block:: C
+
+        struct mei_cl_device_id {
+                char name[MEI_CL_NAME_SIZE];
+                uuid_le uuid;
+                __u8    version;
+                kernel_ulong_t driver_info;
+        };
+
+To actually register a driver on the ME Client bus one must call the :c:func:`mei_cl_add_driver`
+API. This is typically called at module initialization time.
+
+Once the driver is registered and bound to the device, a driver will typically
+try to do some I/O on this bus and this should be done through the :c:func:`mei_cl_send`
+and :c:func:`mei_cl_recv` functions. More detailed information is in :ref:`api` section.
+
+In order for a driver to be notified about pending traffic or event, the driver
+should register a callback via :c:func:`mei_cl_devev_register_rx_cb` and
+:c:func:`mei_cldev_register_notify_cb` function respectively.
+
+.. _api:
+
+API:
+----
+.. kernel-doc:: drivers/misc/mei/bus.c
+    :export: drivers/misc/mei/bus.c
+
+
+
+Example
+=======
+
+As a theoretical example let's pretend the ME comes with a "contact" NFC IP.
+The driver init and exit routines for this device would look like:
+
+.. code-block:: C
+
+        #define CONTACT_DRIVER_NAME "contact"
+
+        static struct mei_cl_device_id contact_mei_cl_tbl[] = {
+                { CONTACT_DRIVER_NAME, },
+
+                /* required last entry */
+                { }
+        };
+        MODULE_DEVICE_TABLE(mei_cl, contact_mei_cl_tbl);
+
+        static struct mei_cl_driver contact_driver = {
+                .id_table = contact_mei_tbl,
+                .name = CONTACT_DRIVER_NAME,
+
+                .probe = contact_probe,
+                .remove = contact_remove,
+        };
+
+        static int contact_init(void)
+        {
+                int r;
+
+                r = mei_cl_driver_register(&contact_driver);
+                if (r) {
+                        pr_err(CONTACT_DRIVER_NAME ": driver registration failed\n");
+                        return r;
+                }
+
+                return 0;
+        }
+
+        static void __exit contact_exit(void)
+        {
+                mei_cl_driver_unregister(&contact_driver);
+        }
+
+        module_init(contact_init);
+        module_exit(contact_exit);
+
+And the driver's simplified probe routine would look like that:
+
+.. code-block:: C
+
+        int contact_probe(struct mei_cl_device *dev, struct mei_cl_device_id *id)
+        {
+                [...]
+                mei_cldev_enable(dev);
+
+                mei_cldev_register_rx_cb(dev, contact_rx_cb);
+
+                return 0;
+        }
+
+In the probe routine the driver first enable the MEI device and then registers
+an rx handler which is as close as it can get to registering a threaded IRQ handler.
+The handler implementation will typically call :c:func:`mei_cldev_recv` and then
+process received data.
+
+.. code-block:: C
+
+        #define MAX_PAYLOAD 128
+        #define HDR_SIZE 4
+        static void conntact_rx_cb(struct mei_cl_device *cldev)
+        {
+                struct contact *c = mei_cldev_get_drvdata(cldev);
+                unsigned char payload[MAX_PAYLOAD];
+                ssize_t payload_sz;
+
+                payload_sz = mei_cldev_recv(cldev, payload,  MAX_PAYLOAD)
+                if (reply_size < HDR_SIZE) {
+                        return;
+                }
+
+                c->process_rx(payload);
+
+        }
+
+MEI Client Bus Drivers
+======================
+
+.. toctree::
+   :maxdepth: 2
+
+   hdcp
+   nfc