Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Intel(R) Management Engine (ME) Client bus API 2 ============================================== 3 4 5 Rationale 6 ========= 7 8 MEI misc character device is useful for dedicated applications to send and receive 9 data to the many FW appliance found in Intel's ME from the user space. 10 However for some of the ME functionalities it make sense to leverage existing software 11 stack and expose them through existing kernel subsystems. 12 13 In order to plug seamlessly into the kernel device driver model we add kernel virtual 14 bus abstraction on top of the MEI driver. This allows implementing linux kernel drivers 15 for the various MEI features as a stand alone entities found in their respective subsystem. 16 Existing device drivers can even potentially be re-used by adding an MEI CL bus layer to 17 the existing code. 18 19 20 MEI CL bus API 21 ============== 22 23 A driver implementation for an MEI Client is very similar to existing bus 24 based device drivers. The driver registers itself as an MEI CL bus driver through 25 the mei_cl_driver structure: 26 27 struct mei_cl_driver { 28 struct device_driver driver; 29 const char *name; 30 31 const struct mei_cl_device_id *id_table; 32 33 int (*probe)(struct mei_cl_device *dev, const struct mei_cl_id *id); 34 int (*remove)(struct mei_cl_device *dev); 35 }; 36 37 struct mei_cl_id { 38 char name[MEI_NAME_SIZE]; 39 kernel_ulong_t driver_info; 40 }; 41 42 The mei_cl_id structure allows the driver to bind itself against a device name. 43 44 To actually register a driver on the ME Client bus one must call the mei_cl_add_driver() 45 API. This is typically called at module init time. 46 47 Once registered on the ME Client bus, a driver will typically try to do some I/O on 48 this bus and this should be done through the mei_cl_send() and mei_cl_recv() 49 routines. The latter is synchronous (blocks and sleeps until data shows up). 50 In order for drivers to be notified of pending events waiting for them (e.g. 51 an Rx event) they can register an event handler through the 52 mei_cl_register_event_cb() routine. Currently only the MEI_EVENT_RX event 53 will trigger an event handler call and the driver implementation is supposed 54 to call mei_recv() from the event handler in order to fetch the pending 55 received buffers. 56 57 58 Example 59 ======= 60 61 As a theoretical example let's pretend the ME comes with a "contact" NFC IP. 62 The driver init and exit routines for this device would look like: 63 64 #define CONTACT_DRIVER_NAME "contact" 65 66 static struct mei_cl_device_id contact_mei_cl_tbl[] = { 67 { CONTACT_DRIVER_NAME, }, 68 69 /* required last entry */ 70 { } 71 }; 72 MODULE_DEVICE_TABLE(mei_cl, contact_mei_cl_tbl); 73 74 static struct mei_cl_driver contact_driver = { 75 .id_table = contact_mei_tbl, 76 .name = CONTACT_DRIVER_NAME, 77 78 .probe = contact_probe, 79 .remove = contact_remove, 80 }; 81 82 static int contact_init(void) 83 { 84 int r; 85 86 r = mei_cl_driver_register(&contact_driver); 87 if (r) { 88 pr_err(CONTACT_DRIVER_NAME ": driver registration failed\n"); 89 return r; 90 } 91 92 return 0; 93 } 94 95 static void __exit contact_exit(void) 96 { 97 mei_cl_driver_unregister(&contact_driver); 98 } 99 100 module_init(contact_init); 101 module_exit(contact_exit); 102 103 And the driver's simplified probe routine would look like that: 104 105 int contact_probe(struct mei_cl_device *dev, struct mei_cl_device_id *id) 106 { 107 struct contact_driver *contact; 108 109 [...] 110 mei_cl_enable_device(dev); 111 112 mei_cl_register_event_cb(dev, contact_event_cb, contact); 113 114 return 0; 115 } 116 117 In the probe routine the driver first enable the MEI device and then registers 118 an ME bus event handler which is as close as it can get to registering a 119 threaded IRQ handler. 120 The handler implementation will typically call some I/O routine depending on 121 the pending events: 122 123 #define MAX_NFC_PAYLOAD 128 124 125 static void contact_event_cb(struct mei_cl_device *dev, u32 events, 126 void *context) 127 { 128 struct contact_driver *contact = context; 129 130 if (events & BIT(MEI_EVENT_RX)) { 131 u8 payload[MAX_NFC_PAYLOAD]; 132 int payload_size; 133 134 payload_size = mei_recv(dev, payload, MAX_NFC_PAYLOAD); 135 if (payload_size <= 0) 136 return; 137 138 /* Hook to the NFC subsystem */ 139 nfc_hci_recv_frame(contact->hdev, payload, payload_size); 140 } 141 }