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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
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Adding upstream version 6.1.76.upstream/6.1.76upstream
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+.. 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