1 .. SPDX-License-Identifier: GPL-2.0
2
3 ==============================================
4 Intel(R) Management Engine (ME) Client bus API
5 ==============================================
6
7
8 Rationale
9 =========
10
11 The MEI character device is useful for dedicated applications to send and receive
12 data to the many FW appliance found in Intel's ME from the user space.
13 However, for some of the ME functionalities it makes sense to leverage existing software
14 stack and expose them through existing kernel subsystems.
15
16 In order to plug seamlessly into the kernel device driver model we add kernel virtual
17 bus abstraction on top of the MEI driver. This allows implementing Linux kernel drivers
18 for the various MEI features as a stand alone entities found in their respective subsystem.
19 Existing device drivers can even potentially be re-used by adding an MEI CL bus layer to
20 the existing code.
21
22
23 MEI CL bus API
24 ==============
25
26 A driver implementation for an MEI Client is very similar to any other existing bus
27 based device drivers. The driver registers itself as an MEI CL bus driver through
28 the ``struct mei_cl_driver`` structure defined in :file:`include/linux/mei_cl_bus.c`
29
30 .. code-block:: C
31
32 struct mei_cl_driver {
33 struct device_driver driver;
34 const char *name;
35
36 const struct mei_cl_device_id *id_table;
37
38 int (*probe)(struct mei_cl_device *dev, const struct mei_cl_id *id);
39 int (*remove)(struct mei_cl_device *dev);
40 };
41
42
43
44 The mei_cl_device_id structure defined in :file:`include/linux/mod_devicetable.h` allows a
45 driver to bind itself against a device name.
46
47 .. code-block:: C
48
49 struct mei_cl_device_id {
50 char name[MEI_CL_NAME_SIZE];
51 uuid_le uuid;
52 __u8 version;
53 kernel_ulong_t driver_info;
54 };
55
56 To actually register a driver on the ME Client bus one must call the :c:func:`mei_cl_add_driver`
57 API. This is typically called at module initialization time.
58
59 Once the driver is registered and bound to the device, a driver will typically
60 try to do some I/O on this bus and this should be done through the :c:func:`mei_cl_send`
61 and :c:func:`mei_cl_recv` functions. More detailed information is in :ref:`api` section.
62
63 In order for a driver to be notified about pending traffic or event, the driver
64 should register a callback via :c:func:`mei_cl_devev_register_rx_cb` and
65 :c:func:`mei_cldev_register_notify_cb` function respectively.
66
67 .. _api:
68
69 API:
70 ----
71 .. kernel-doc:: drivers/misc/mei/bus.c
72 :export: drivers/misc/mei/bus.c
73
74
75
76 Example
77 =======
78
79 As a theoretical example let's pretend the ME comes with a "contact" NFC IP.
80 The driver init and exit routines for this device would look like:
81
82 .. code-block:: C
83
84 #define CONTACT_DRIVER_NAME "contact"
85
86 static struct mei_cl_device_id contact_mei_cl_tbl[] = {
87 { CONTACT_DRIVER_NAME, },
88
89 /* required last entry */
90 { }
91 };
92 MODULE_DEVICE_TABLE(mei_cl, contact_mei_cl_tbl);
93
94 static struct mei_cl_driver contact_driver = {
95 .id_table = contact_mei_tbl,
96 .name = CONTACT_DRIVER_NAME,
97
98 .probe = contact_probe,
99 .remove = contact_remove,
100 };
101
102 static int contact_init(void)
103 {
104 int r;
105
106 r = mei_cl_driver_register(&contact_driver);
107 if (r) {
108 pr_err(CONTACT_DRIVER_NAME ": driver registration failed\n");
109 return r;
110 }
111
112 return 0;
113 }
114
115 static void __exit contact_exit(void)
116 {
117 mei_cl_driver_unregister(&contact_driver);
118 }
119
120 module_init(contact_init);
121 module_exit(contact_exit);
122
123 And the driver's simplified probe routine would look like that:
124
125 .. code-block:: C
126
127 int contact_probe(struct mei_cl_device *dev, struct mei_cl_device_id *id)
128 {
129 [...]
130 mei_cldev_enable(dev);
131
132 mei_cldev_register_rx_cb(dev, contact_rx_cb);
133
134 return 0;
135 }
136
137 In the probe routine the driver first enable the MEI device and then registers
138 an rx handler which is as close as it can get to registering a threaded IRQ handler.
139 The handler implementation will typically call :c:func:`mei_cldev_recv` and then
140 process received data.
141
142 .. code-block:: C
143
144 #define MAX_PAYLOAD 128
145 #define HDR_SIZE 4
146 static void conntact_rx_cb(struct mei_cl_device *cldev)
147 {
148 struct contact *c = mei_cldev_get_drvdata(cldev);
149 unsigned char payload[MAX_PAYLOAD];
150 ssize_t payload_sz;
151
152 payload_sz = mei_cldev_recv(cldev, payload, MAX_PAYLOAD)
153 if (reply_size < HDR_SIZE) {
154 return;
155 }
156
157 c->process_rx(payload);
158
159 }
160
161 MEI Client Bus Drivers
162 ======================
163
164 .. toctree::
165 :maxdepth: 2
166
167 hdcp
168 nfc
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