1================================= 2Intel Integrated Sensor Hub (ISH) 3================================= 4 5A sensor hub enables the ability to offload sensor polling and algorithm 6processing to a dedicated low power co-processor. This allows the core 7processor to go into low power modes more often, resulting in increased 8battery life. 9 10There are many vendors providing external sensor hubs conforming to HID 11Sensor usage tables. These may be found in tablets, 2-in-1 convertible laptops 12and embedded products. Linux has had this support since Linux 3.9. 13 14Intel® introduced integrated sensor hubs as a part of the SoC starting from 15Cherry Trail and now supported on multiple generations of CPU packages. There 16are many commercial devices already shipped with Integrated Sensor Hubs (ISH). 17These ISH also comply to HID sensor specification, but the difference is the 18transport protocol used for communication. The current external sensor hubs 19mainly use HID over I2C or USB. But ISH doesn't use either I2C or USB. 20 211. Overview 22=========== 23 24Using a analogy with a usbhid implementation, the ISH follows a similar model 25for a very high speed communication:: 26 27 ----------------- ---------------------- 28 | USB HID | --> | ISH HID | 29 ----------------- ---------------------- 30 ----------------- ---------------------- 31 | USB protocol | --> | ISH Transport | 32 ----------------- ---------------------- 33 ----------------- ---------------------- 34 | EHCI/XHCI | --> | ISH IPC | 35 ----------------- ---------------------- 36 PCI PCI 37 ----------------- ---------------------- 38 |Host controller| --> | ISH processor | 39 ----------------- ---------------------- 40 USB Link 41 ----------------- ---------------------- 42 | USB End points| --> | ISH Clients | 43 ----------------- ---------------------- 44 45Like USB protocol provides a method for device enumeration, link management 46and user data encapsulation, the ISH also provides similar services. But it is 47very light weight tailored to manage and communicate with ISH client 48applications implemented in the firmware. 49 50The ISH allows multiple sensor management applications executing in the 51firmware. Like USB endpoints the messaging can be to/from a client. As part of 52enumeration process, these clients are identified. These clients can be simple 53HID sensor applications, sensor calibration applications or sensor firmware 54update applications. 55 56The implementation model is similar, like USB bus, ISH transport is also 57implemented as a bus. Each client application executing in the ISH processor 58is registered as a device on this bus. The driver, which binds each device 59(ISH HID driver) identifies the device type and registers with the HID core. 60 612. ISH Implementation: Block Diagram 62==================================== 63 64:: 65 66 --------------------------- 67 | User Space Applications | 68 --------------------------- 69 70 ----------------IIO ABI---------------- 71 -------------------------- 72 | IIO Sensor Drivers | 73 -------------------------- 74 -------------------------- 75 | IIO core | 76 -------------------------- 77 -------------------------- 78 | HID Sensor Hub MFD | 79 -------------------------- 80 -------------------------- 81 | HID Core | 82 -------------------------- 83 -------------------------- 84 | HID over ISH Client | 85 -------------------------- 86 -------------------------- 87 | ISH Transport (ISHTP) | 88 -------------------------- 89 -------------------------- 90 | IPC Drivers | 91 -------------------------- 92 OS 93 ---------------- PCI ----------------- 94 Hardware + Firmware 95 ---------------------------- 96 | ISH Hardware/Firmware(FW) | 97 ---------------------------- 98 993. High level processing in above blocks 100======================================== 101 1023.1 Hardware Interface 103---------------------- 104 105The ISH is exposed as "Non-VGA unclassified PCI device" to the host. The PCI 106product and vendor IDs are changed from different generations of processors. So 107the source code which enumerates drivers needs to update from generation to 108generation. 109 1103.2 Inter Processor Communication (IPC) driver 111---------------------------------------------- 112 113Location: drivers/hid/intel-ish-hid/ipc 114 115The IPC message uses memory mapped I/O. The registers are defined in 116hw-ish-regs.h. 117 1183.2.1 IPC/FW message types 119^^^^^^^^^^^^^^^^^^^^^^^^^^ 120 121There are two types of messages, one for management of link and another for 122messages to and from transport layers. 123 124TX and RX of Transport messages 125............................... 126 127A set of memory mapped register offers support of multi-byte messages TX and 128RX (e.g. IPC_REG_ISH2HOST_MSG, IPC_REG_HOST2ISH_MSG). The IPC layer maintains 129internal queues to sequence messages and send them in order to the firmware. 130Optionally the caller can register handler to get notification of completion. 131A doorbell mechanism is used in messaging to trigger processing in host and 132client firmware side. When ISH interrupt handler is called, the ISH2HOST 133doorbell register is used by host drivers to determine that the interrupt 134is for ISH. 135 136Each side has 32 32-bit message registers and a 32-bit doorbell. Doorbell 137register has the following format:: 138 139 Bits 0..6: fragment length (7 bits are used) 140 Bits 10..13: encapsulated protocol 141 Bits 16..19: management command (for IPC management protocol) 142 Bit 31: doorbell trigger (signal H/W interrupt to the other side) 143 Other bits are reserved, should be 0. 144 1453.2.2 Transport layer interface 146^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 147 148To abstract HW level IPC communication, a set of callbacks is registered. 149The transport layer uses them to send and receive messages. 150Refer to struct ishtp_hw_ops for callbacks. 151 1523.3 ISH Transport layer 153----------------------- 154 155Location: drivers/hid/intel-ish-hid/ishtp/ 156 1573.3.1 A Generic Transport Layer 158^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 159 160The transport layer is a bi-directional protocol, which defines: 161- Set of commands to start, stop, connect, disconnect and flow control 162(see ishtp/hbm.h for details) 163- A flow control mechanism to avoid buffer overflows 164 165This protocol resembles bus messages described in the following document: 166http://www.intel.com/content/dam/www/public/us/en/documents/technical-\ 167specifications/dcmi-hi-1-0-spec.pdf "Chapter 7: Bus Message Layer" 168 1693.3.2 Connection and Flow Control Mechanism 170^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 171 172Each FW client and a protocol is identified by a UUID. In order to communicate 173to a FW client, a connection must be established using connect request and 174response bus messages. If successful, a pair (host_client_id and fw_client_id) 175will identify the connection. 176 177Once connection is established, peers send each other flow control bus messages 178independently. Every peer may send a message only if it has received a 179flow-control credit before. Once it has sent a message, it may not send another one 180before receiving the next flow control credit. 181Either side can send disconnect request bus message to end communication. Also 182the link will be dropped if major FW reset occurs. 183 1843.3.3 Peer to Peer data transfer 185^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 186 187Peer to Peer data transfer can happen with or without using DMA. Depending on 188the sensor bandwidth requirement DMA can be enabled by using module parameter 189ishtp_use_dma under intel_ishtp. 190 191Each side (host and FW) manages its DMA transfer memory independently. When an 192ISHTP client from either host or FW side wants to send something, it decides 193whether to send over IPC or over DMA; for each transfer the decision is 194independent. The sending side sends DMA_XFER message when the message is in 195the respective host buffer (TX when host client sends, RX when FW client 196sends). The recipient of DMA message responds with DMA_XFER_ACK, indicating 197the sender that the memory region for that message may be reused. 198 199DMA initialization is started with host sending DMA_ALLOC_NOTIFY bus message 200(that includes RX buffer) and FW responds with DMA_ALLOC_NOTIFY_ACK. 201Additionally to DMA address communication, this sequence checks capabilities: 202if thw host doesn't support DMA, then it won't send DMA allocation, so FW can't 203send DMA; if FW doesn't support DMA then it won't respond with 204DMA_ALLOC_NOTIFY_ACK, in which case host will not use DMA transfers. 205Here ISH acts as busmaster DMA controller. Hence when host sends DMA_XFER, 206it's request to do host->ISH DMA transfer; when FW sends DMA_XFER, it means 207that it already did DMA and the message resides at host. Thus, DMA_XFER 208and DMA_XFER_ACK act as ownership indicators. 209 210At initial state all outgoing memory belongs to the sender (TX to host, RX to 211FW), DMA_XFER transfers ownership on the region that contains ISHTP message to 212the receiving side, DMA_XFER_ACK returns ownership to the sender. A sender 213need not wait for previous DMA_XFER to be ack'ed, and may send another message 214as long as remaining continuous memory in its ownership is enough. 215In principle, multiple DMA_XFER and DMA_XFER_ACK messages may be sent at once 216(up to IPC MTU), thus allowing for interrupt throttling. 217Currently, ISH FW decides to send over DMA if ISHTP message is more than 3 IPC 218fragments and via IPC otherwise. 219 2203.3.4 Ring Buffers 221^^^^^^^^^^^^^^^^^^ 222 223When a client initiates a connection, a ring of RX and TX buffers is allocated. 224The size of ring can be specified by the client. HID client sets 16 and 32 for 225TX and RX buffers respectively. On send request from client, the data to be 226sent is copied to one of the send ring buffer and scheduled to be sent using 227bus message protocol. These buffers are required because the FW may have not 228have processed the last message and may not have enough flow control credits 229to send. Same thing holds true on receive side and flow control is required. 230 2313.3.5 Host Enumeration 232^^^^^^^^^^^^^^^^^^^^^^ 233 234The host enumeration bus command allows discovery of clients present in the FW. 235There can be multiple sensor clients and clients for calibration function. 236 237To ease implementation and allow independent drivers to handle each client, 238this transport layer takes advantage of Linux Bus driver model. Each 239client is registered as device on the transport bus (ishtp bus). 240 241Enumeration sequence of messages: 242 243- Host sends HOST_START_REQ_CMD, indicating that host ISHTP layer is up. 244- FW responds with HOST_START_RES_CMD 245- Host sends HOST_ENUM_REQ_CMD (enumerate FW clients) 246- FW responds with HOST_ENUM_RES_CMD that includes bitmap of available FW 247 client IDs 248- For each FW ID found in that bitmap host sends 249 HOST_CLIENT_PROPERTIES_REQ_CMD 250- FW responds with HOST_CLIENT_PROPERTIES_RES_CMD. Properties include UUID, 251 max ISHTP message size, etc. 252- Once host received properties for that last discovered client, it considers 253 ISHTP device fully functional (and allocates DMA buffers) 254 2553.4 HID over ISH Client 256----------------------- 257 258Location: drivers/hid/intel-ish-hid 259 260The ISHTP client driver is responsible for: 261 262- enumerate HID devices under FW ISH client 263- Get Report descriptor 264- Register with HID core as a LL driver 265- Process Get/Set feature request 266- Get input reports 267 2683.5 HID Sensor Hub MFD and IIO sensor drivers 269--------------------------------------------- 270 271The functionality in these drivers is the same as an external sensor hub. 272Refer to 273Documentation/hid/hid-sensor.rst for HID sensor 274Documentation/ABI/testing/sysfs-bus-iio for IIO ABIs to user space. 275 2763.6 End to End HID transport Sequence Diagram 277--------------------------------------------- 278 279:: 280 281 HID-ISH-CLN ISHTP IPC HW 282 | | | | 283 | | |-----WAKE UP------------------>| 284 | | | | 285 | | |-----HOST READY--------------->| 286 | | | | 287 | | |<----MNG_RESET_NOTIFY_ACK----- | 288 | | | | 289 | |<----ISHTP_START------ | | 290 | | | | 291 | |<-----------------HOST_START_RES_CMD-------------------| 292 | | | | 293 | |------------------QUERY_SUBSCRIBER-------------------->| 294 | | | | 295 | |------------------HOST_ENUM_REQ_CMD------------------->| 296 | | | | 297 | |<-----------------HOST_ENUM_RES_CMD--------------------| 298 | | | | 299 | |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>| 300 | | | | 301 | |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------| 302 | Create new device on in ishtp bus | | 303 | | | | 304 | |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>| 305 | | | | 306 | |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------| 307 | Create new device on in ishtp bus | | 308 | | | | 309 | |--Repeat HOST_CLIENT_PROPERTIES_REQ_CMD-till last one--| 310 | | | | 311 probed() 312 |----ishtp_cl_connect--->|----------------- CLIENT_CONNECT_REQ_CMD-------------->| 313 | | | | 314 | |<----------------CLIENT_CONNECT_RES_CMD----------------| 315 | | | | 316 |register event callback | | | 317 | | | | 318 |ishtp_cl_send( 319 HOSTIF_DM_ENUM_DEVICES) |----------fill ishtp_msg_hdr struct write to HW----- >| 320 | | | | 321 | | |<-----IRQ(IPC_PROTOCOL_ISHTP---| 322 | | | | 323 |<--ENUM_DEVICE RSP------| | | 324 | | | | 325 for each enumerated device 326 |ishtp_cl_send( 327 HOSTIF_GET_HID_DESCRIPTOR|----------fill ishtp_msg_hdr struct write to HW----- >| 328 | | | | 329 ...Response 330 | | | | 331 for each enumerated device 332 |ishtp_cl_send( 333 HOSTIF_GET_REPORT_DESCRIPTOR|--------------fill ishtp_msg_hdr struct write to HW-- >| 334 | | | | 335 | | | | 336 hid_allocate_device 337 | | | | 338 hid_add_device | | | 339 | | | | 340 341 3423.7 ISH Debugging 343----------------- 344 345To debug ISH, event tracing mechanism is used. To enable debug logs:: 346 347 echo 1 > /sys/kernel/debug/tracing/events/intel_ish/enable 348 cat /sys/kernel/debug/tracing/trace 349 3503.8 ISH IIO sysfs Example on Lenovo thinkpad Yoga 260 351----------------------------------------------------- 352 353:: 354 355 root@otcpl-ThinkPad-Yoga-260:~# tree -l /sys/bus/iio/devices/ 356 /sys/bus/iio/devices/ 357 ├── iio:device0 -> ../../../devices/0044:8086:22D8.0001/HID-SENSOR-200073.9.auto/iio:device0 358 │ ├── buffer 359 │ │ ├── enable 360 │ │ ├── length 361 │ │ └── watermark 362 ... 363 │ ├── in_accel_hysteresis 364 │ ├── in_accel_offset 365 │ ├── in_accel_sampling_frequency 366 │ ├── in_accel_scale 367 │ ├── in_accel_x_raw 368 │ ├── in_accel_y_raw 369 │ ├── in_accel_z_raw 370 │ ├── name 371 │ ├── scan_elements 372 │ │ ├── in_accel_x_en 373 │ │ ├── in_accel_x_index 374 │ │ ├── in_accel_x_type 375 │ │ ├── in_accel_y_en 376 │ │ ├── in_accel_y_index 377 │ │ ├── in_accel_y_type 378 │ │ ├── in_accel_z_en 379 │ │ ├── in_accel_z_index 380 │ │ └── in_accel_z_type 381 ... 382 │ │ ├── devices 383 │ │ │ │ ├── buffer 384 │ │ │ │ │ ├── enable 385 │ │ │ │ │ ├── length 386 │ │ │ │ │ └── watermark 387 │ │ │ │ ├── dev 388 │ │ │ │ ├── in_intensity_both_raw 389 │ │ │ │ ├── in_intensity_hysteresis 390 │ │ │ │ ├── in_intensity_offset 391 │ │ │ │ ├── in_intensity_sampling_frequency 392 │ │ │ │ ├── in_intensity_scale 393 │ │ │ │ ├── name 394 │ │ │ │ ├── scan_elements 395 │ │ │ │ │ ├── in_intensity_both_en 396 │ │ │ │ │ ├── in_intensity_both_index 397 │ │ │ │ │ └── in_intensity_both_type 398 │ │ │ │ ├── trigger 399 │ │ │ │ │ └── current_trigger 400 ... 401 │ │ │ │ ├── buffer 402 │ │ │ │ │ ├── enable 403 │ │ │ │ │ ├── length 404 │ │ │ │ │ └── watermark 405 │ │ │ │ ├── dev 406 │ │ │ │ ├── in_magn_hysteresis 407 │ │ │ │ ├── in_magn_offset 408 │ │ │ │ ├── in_magn_sampling_frequency 409 │ │ │ │ ├── in_magn_scale 410 │ │ │ │ ├── in_magn_x_raw 411 │ │ │ │ ├── in_magn_y_raw 412 │ │ │ │ ├── in_magn_z_raw 413 │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_raw 414 │ │ │ │ ├── in_rot_hysteresis 415 │ │ │ │ ├── in_rot_offset 416 │ │ │ │ ├── in_rot_sampling_frequency 417 │ │ │ │ ├── in_rot_scale 418 │ │ │ │ ├── name 419 ... 420 │ │ │ │ ├── scan_elements 421 │ │ │ │ │ ├── in_magn_x_en 422 │ │ │ │ │ ├── in_magn_x_index 423 │ │ │ │ │ ├── in_magn_x_type 424 │ │ │ │ │ ├── in_magn_y_en 425 │ │ │ │ │ ├── in_magn_y_index 426 │ │ │ │ │ ├── in_magn_y_type 427 │ │ │ │ │ ├── in_magn_z_en 428 │ │ │ │ │ ├── in_magn_z_index 429 │ │ │ │ │ ├── in_magn_z_type 430 │ │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_en 431 │ │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_index 432 │ │ │ │ │ └── in_rot_from_north_magnetic_tilt_comp_type 433 │ │ │ │ ├── trigger 434 │ │ │ │ │ └── current_trigger 435 ... 436 │ │ │ │ ├── buffer 437 │ │ │ │ │ ├── enable 438 │ │ │ │ │ ├── length 439 │ │ │ │ │ └── watermark 440 │ │ │ │ ├── dev 441 │ │ │ │ ├── in_anglvel_hysteresis 442 │ │ │ │ ├── in_anglvel_offset 443 │ │ │ │ ├── in_anglvel_sampling_frequency 444 │ │ │ │ ├── in_anglvel_scale 445 │ │ │ │ ├── in_anglvel_x_raw 446 │ │ │ │ ├── in_anglvel_y_raw 447 │ │ │ │ ├── in_anglvel_z_raw 448 │ │ │ │ ├── name 449 │ │ │ │ ├── scan_elements 450 │ │ │ │ │ ├── in_anglvel_x_en 451 │ │ │ │ │ ├── in_anglvel_x_index 452 │ │ │ │ │ ├── in_anglvel_x_type 453 │ │ │ │ │ ├── in_anglvel_y_en 454 │ │ │ │ │ ├── in_anglvel_y_index 455 │ │ │ │ │ ├── in_anglvel_y_type 456 │ │ │ │ │ ├── in_anglvel_z_en 457 │ │ │ │ │ ├── in_anglvel_z_index 458 │ │ │ │ │ └── in_anglvel_z_type 459 │ │ │ │ ├── trigger 460 │ │ │ │ │ └── current_trigger 461 ... 462 │ │ │ │ ├── buffer 463 │ │ │ │ │ ├── enable 464 │ │ │ │ │ ├── length 465 │ │ │ │ │ └── watermark 466 │ │ │ │ ├── dev 467 │ │ │ │ ├── in_anglvel_hysteresis 468 │ │ │ │ ├── in_anglvel_offset 469 │ │ │ │ ├── in_anglvel_sampling_frequency 470 │ │ │ │ ├── in_anglvel_scale 471 │ │ │ │ ├── in_anglvel_x_raw 472 │ │ │ │ ├── in_anglvel_y_raw 473 │ │ │ │ ├── in_anglvel_z_raw 474 │ │ │ │ ├── name 475 │ │ │ │ ├── scan_elements 476 │ │ │ │ │ ├── in_anglvel_x_en 477 │ │ │ │ │ ├── in_anglvel_x_index 478 │ │ │ │ │ ├── in_anglvel_x_type 479 │ │ │ │ │ ├── in_anglvel_y_en 480 │ │ │ │ │ ├── in_anglvel_y_index 481 │ │ │ │ │ ├── in_anglvel_y_type 482 │ │ │ │ │ ├── in_anglvel_z_en 483 │ │ │ │ │ ├── in_anglvel_z_index 484 │ │ │ │ │ └── in_anglvel_z_type 485 │ │ │ │ ├── trigger 486 │ │ │ │ │ └── current_trigger 487 ... 488