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-Intel(R) Management Engine (ME) Client bus API
-==============================================
-
-
-Rationale
-=========
-
-MEI misc 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 make 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 existing bus
-based device drivers. The driver registers itself as an MEI CL bus driver through
-the mei_cl_driver structure:
-
-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);
-};
-
-struct mei_cl_id {
- char name[MEI_NAME_SIZE];
- kernel_ulong_t driver_info;
-};
-
-The mei_cl_id structure allows the driver to bind itself against a device name.
-
-To actually register a driver on the ME Client bus one must call the mei_cl_add_driver()
-API. This is typically called at module init time.
-
-Once registered on the ME Client bus, a driver will typically try to do some I/O on
-this bus and this should be done through the mei_cl_send() and mei_cl_recv()
-routines. The latter is synchronous (blocks and sleeps until data shows up).
-In order for drivers to be notified of pending events waiting for them (e.g.
-an Rx event) they can register an event handler through the
-mei_cl_register_event_cb() routine. Currently only the MEI_EVENT_RX event
-will trigger an event handler call and the driver implementation is supposed
-to call mei_recv() from the event handler in order to fetch the pending
-received buffers.
-
-
-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:
-
-#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:
-
-int contact_probe(struct mei_cl_device *dev, struct mei_cl_device_id *id)
-{
- struct contact_driver *contact;
-
- [...]
- mei_cl_enable_device(dev);
-
- mei_cl_register_event_cb(dev, contact_event_cb, contact);
-
- return 0;
-}
-
-In the probe routine the driver first enable the MEI device and then registers
-an ME bus event handler which is as close as it can get to registering a
-threaded IRQ handler.
-The handler implementation will typically call some I/O routine depending on
-the pending events:
-
-#define MAX_NFC_PAYLOAD 128
-
-static void contact_event_cb(struct mei_cl_device *dev, u32 events,
- void *context)
-{
- struct contact_driver *contact = context;
-
- if (events & BIT(MEI_EVENT_RX)) {
- u8 payload[MAX_NFC_PAYLOAD];
- int payload_size;
-
- payload_size = mei_recv(dev, payload, MAX_NFC_PAYLOAD);
- if (payload_size <= 0)
- return;
-
- /* Hook to the NFC subsystem */
- nfc_hci_recv_frame(contact->hdev, payload, payload_size);
- }
-}