1 files changed, 138 insertions, 0 deletions
diff --git a/Documentation/misc-devices/mei/mei-client-bus.txt b/Documentation/misc-devices/mei/mei-client-bus.txt
new file mode 100644
index 000000000000..f83910a8ce76
--- /dev/null
+++ b/Documentation/misc-devices/mei/mei-client-bus.txt
@@ -0,0 +1,138 @@
+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);
+	}
+}