| ================================= |
| Intel Integrated Sensor Hub (ISH) |
| ================================= |
| |
| A sensor hub enables the ability to offload sensor polling and algorithm |
| processing to a dedicated low power co-processor. This allows the core |
| processor to go into low power modes more often, resulting in increased |
| battery life. |
| |
| There are many vendors providing external sensor hubs conforming to HID |
| Sensor usage tables. These may be found in tablets, 2-in-1 convertible laptops |
| and embedded products. Linux has had this support since Linux 3.9. |
| |
| Intel® introduced integrated sensor hubs as a part of the SoC starting from |
| Cherry Trail and now supported on multiple generations of CPU packages. There |
| are many commercial devices already shipped with Integrated Sensor Hubs (ISH). |
| These ISH also comply to HID sensor specification, but the difference is the |
| transport protocol used for communication. The current external sensor hubs |
| mainly use HID over I2C or USB. But ISH doesn't use either I2C or USB. |
| |
| 1. Overview |
| =========== |
| |
| Using a analogy with a usbhid implementation, the ISH follows a similar model |
| for a very high speed communication:: |
| |
| ----------------- ---------------------- |
| | USB HID | --> | ISH HID | |
| ----------------- ---------------------- |
| ----------------- ---------------------- |
| | USB protocol | --> | ISH Transport | |
| ----------------- ---------------------- |
| ----------------- ---------------------- |
| | EHCI/XHCI | --> | ISH IPC | |
| ----------------- ---------------------- |
| PCI PCI |
| ----------------- ---------------------- |
| |Host controller| --> | ISH processor | |
| ----------------- ---------------------- |
| USB Link |
| ----------------- ---------------------- |
| | USB End points| --> | ISH Clients | |
| ----------------- ---------------------- |
| |
| Like USB protocol provides a method for device enumeration, link management |
| and user data encapsulation, the ISH also provides similar services. But it is |
| very light weight tailored to manage and communicate with ISH client |
| applications implemented in the firmware. |
| |
| The ISH allows multiple sensor management applications executing in the |
| firmware. Like USB endpoints the messaging can be to/from a client. As part of |
| enumeration process, these clients are identified. These clients can be simple |
| HID sensor applications, sensor calibration applications or sensor firmware |
| update applications. |
| |
| The implementation model is similar, like USB bus, ISH transport is also |
| implemented as a bus. Each client application executing in the ISH processor |
| is registered as a device on this bus. The driver, which binds each device |
| (ISH HID driver) identifies the device type and registers with the HID core. |
| |
| 2. ISH Implementation: Block Diagram |
| ==================================== |
| |
| :: |
| |
| --------------------------- |
| | User Space Applications | |
| --------------------------- |
| |
| ----------------IIO ABI---------------- |
| -------------------------- |
| | IIO Sensor Drivers | |
| -------------------------- |
| -------------------------- |
| | IIO core | |
| -------------------------- |
| -------------------------- |
| | HID Sensor Hub MFD | |
| -------------------------- |
| -------------------------- |
| | HID Core | |
| -------------------------- |
| -------------------------- |
| | HID over ISH Client | |
| -------------------------- |
| -------------------------- |
| | ISH Transport (ISHTP) | |
| -------------------------- |
| -------------------------- |
| | IPC Drivers | |
| -------------------------- |
| OS |
| ---------------- PCI ----------------- |
| Hardware + Firmware |
| ---------------------------- |
| | ISH Hardware/Firmware(FW) | |
| ---------------------------- |
| |
| 3. High level processing in above blocks |
| ======================================== |
| |
| 3.1 Hardware Interface |
| ---------------------- |
| |
| The ISH is exposed as "Non-VGA unclassified PCI device" to the host. The PCI |
| product and vendor IDs are changed from different generations of processors. So |
| the source code which enumerates drivers needs to update from generation to |
| generation. |
| |
| 3.2 Inter Processor Communication (IPC) driver |
| ---------------------------------------------- |
| |
| Location: drivers/hid/intel-ish-hid/ipc |
| |
| The IPC message uses memory mapped I/O. The registers are defined in |
| hw-ish-regs.h. |
| |
| 3.2.1 IPC/FW message types |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| There are two types of messages, one for management of link and another for |
| messages to and from transport layers. |
| |
| TX and RX of Transport messages |
| ............................... |
| |
| A set of memory mapped register offers support of multi-byte messages TX and |
| RX (e.g. IPC_REG_ISH2HOST_MSG, IPC_REG_HOST2ISH_MSG). The IPC layer maintains |
| internal queues to sequence messages and send them in order to the firmware. |
| Optionally the caller can register handler to get notification of completion. |
| A doorbell mechanism is used in messaging to trigger processing in host and |
| client firmware side. When ISH interrupt handler is called, the ISH2HOST |
| doorbell register is used by host drivers to determine that the interrupt |
| is for ISH. |
| |
| Each side has 32 32-bit message registers and a 32-bit doorbell. Doorbell |
| register has the following format:: |
| |
| Bits 0..6: fragment length (7 bits are used) |
| Bits 10..13: encapsulated protocol |
| Bits 16..19: management command (for IPC management protocol) |
| Bit 31: doorbell trigger (signal H/W interrupt to the other side) |
| Other bits are reserved, should be 0. |
| |
| 3.2.2 Transport layer interface |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| To abstract HW level IPC communication, a set of callbacks is registered. |
| The transport layer uses them to send and receive messages. |
| Refer to struct ishtp_hw_ops for callbacks. |
| |
| 3.3 ISH Transport layer |
| ----------------------- |
| |
| Location: drivers/hid/intel-ish-hid/ishtp/ |
| |
| 3.3.1 A Generic Transport Layer |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The transport layer is a bi-directional protocol, which defines: |
| - Set of commands to start, stop, connect, disconnect and flow control |
| (see ishtp/hbm.h for details) |
| - A flow control mechanism to avoid buffer overflows |
| |
| This protocol resembles bus messages described in the following document: |
| http://www.intel.com/content/dam/www/public/us/en/documents/technical-\ |
| specifications/dcmi-hi-1-0-spec.pdf "Chapter 7: Bus Message Layer" |
| |
| 3.3.2 Connection and Flow Control Mechanism |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Each FW client and a protocol is identified by a UUID. In order to communicate |
| to a FW client, a connection must be established using connect request and |
| response bus messages. If successful, a pair (host_client_id and fw_client_id) |
| will identify the connection. |
| |
| Once connection is established, peers send each other flow control bus messages |
| independently. Every peer may send a message only if it has received a |
| flow-control credit before. Once it has sent a message, it may not send another one |
| before receiving the next flow control credit. |
| Either side can send disconnect request bus message to end communication. Also |
| the link will be dropped if major FW reset occurs. |
| |
| 3.3.3 Peer to Peer data transfer |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Peer to Peer data transfer can happen with or without using DMA. Depending on |
| the sensor bandwidth requirement DMA can be enabled by using module parameter |
| ishtp_use_dma under intel_ishtp. |
| |
| Each side (host and FW) manages its DMA transfer memory independently. When an |
| ISHTP client from either host or FW side wants to send something, it decides |
| whether to send over IPC or over DMA; for each transfer the decision is |
| independent. The sending side sends DMA_XFER message when the message is in |
| the respective host buffer (TX when host client sends, RX when FW client |
| sends). The recipient of DMA message responds with DMA_XFER_ACK, indicating |
| the sender that the memory region for that message may be reused. |
| |
| DMA initialization is started with host sending DMA_ALLOC_NOTIFY bus message |
| (that includes RX buffer) and FW responds with DMA_ALLOC_NOTIFY_ACK. |
| Additionally to DMA address communication, this sequence checks capabilities: |
| if the host doesn't support DMA, then it won't send DMA allocation, so FW can't |
| send DMA; if FW doesn't support DMA then it won't respond with |
| DMA_ALLOC_NOTIFY_ACK, in which case host will not use DMA transfers. |
| Here ISH acts as busmaster DMA controller. Hence when host sends DMA_XFER, |
| it's request to do host->ISH DMA transfer; when FW sends DMA_XFER, it means |
| that it already did DMA and the message resides at host. Thus, DMA_XFER |
| and DMA_XFER_ACK act as ownership indicators. |
| |
| At initial state all outgoing memory belongs to the sender (TX to host, RX to |
| FW), DMA_XFER transfers ownership on the region that contains ISHTP message to |
| the receiving side, DMA_XFER_ACK returns ownership to the sender. A sender |
| need not wait for previous DMA_XFER to be ack'ed, and may send another message |
| as long as remaining continuous memory in its ownership is enough. |
| In principle, multiple DMA_XFER and DMA_XFER_ACK messages may be sent at once |
| (up to IPC MTU), thus allowing for interrupt throttling. |
| Currently, ISH FW decides to send over DMA if ISHTP message is more than 3 IPC |
| fragments and via IPC otherwise. |
| |
| 3.3.4 Ring Buffers |
| ^^^^^^^^^^^^^^^^^^ |
| |
| When a client initiates a connection, a ring of RX and TX buffers is allocated. |
| The size of ring can be specified by the client. HID client sets 16 and 32 for |
| TX and RX buffers respectively. On send request from client, the data to be |
| sent is copied to one of the send ring buffer and scheduled to be sent using |
| bus message protocol. These buffers are required because the FW may have not |
| have processed the last message and may not have enough flow control credits |
| to send. Same thing holds true on receive side and flow control is required. |
| |
| 3.3.5 Host Enumeration |
| ^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The host enumeration bus command allows discovery of clients present in the FW. |
| There can be multiple sensor clients and clients for calibration function. |
| |
| To ease implementation and allow independent drivers to handle each client, |
| this transport layer takes advantage of Linux Bus driver model. Each |
| client is registered as device on the transport bus (ishtp bus). |
| |
| Enumeration sequence of messages: |
| |
| - Host sends HOST_START_REQ_CMD, indicating that host ISHTP layer is up. |
| - FW responds with HOST_START_RES_CMD |
| - Host sends HOST_ENUM_REQ_CMD (enumerate FW clients) |
| - FW responds with HOST_ENUM_RES_CMD that includes bitmap of available FW |
| client IDs |
| - For each FW ID found in that bitmap host sends |
| HOST_CLIENT_PROPERTIES_REQ_CMD |
| - FW responds with HOST_CLIENT_PROPERTIES_RES_CMD. Properties include UUID, |
| max ISHTP message size, etc. |
| - Once host received properties for that last discovered client, it considers |
| ISHTP device fully functional (and allocates DMA buffers) |
| |
| 3.4 HID over ISH Client |
| ----------------------- |
| |
| Location: drivers/hid/intel-ish-hid |
| |
| The ISHTP client driver is responsible for: |
| |
| - enumerate HID devices under FW ISH client |
| - Get Report descriptor |
| - Register with HID core as a LL driver |
| - Process Get/Set feature request |
| - Get input reports |
| |
| 3.5 HID Sensor Hub MFD and IIO sensor drivers |
| --------------------------------------------- |
| |
| The functionality in these drivers is the same as an external sensor hub. |
| Refer to |
| Documentation/hid/hid-sensor.rst for HID sensor |
| Documentation/ABI/testing/sysfs-bus-iio for IIO ABIs to user space. |
| |
| 3.6 End to End HID transport Sequence Diagram |
| --------------------------------------------- |
| |
| :: |
| |
| HID-ISH-CLN ISHTP IPC HW |
| | | | | |
| | | |-----WAKE UP------------------>| |
| | | | | |
| | | |-----HOST READY--------------->| |
| | | | | |
| | | |<----MNG_RESET_NOTIFY_ACK----- | |
| | | | | |
| | |<----ISHTP_START------ | | |
| | | | | |
| | |<-----------------HOST_START_RES_CMD-------------------| |
| | | | | |
| | |------------------QUERY_SUBSCRIBER-------------------->| |
| | | | | |
| | |------------------HOST_ENUM_REQ_CMD------------------->| |
| | | | | |
| | |<-----------------HOST_ENUM_RES_CMD--------------------| |
| | | | | |
| | |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>| |
| | | | | |
| | |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------| |
| | Create new device on in ishtp bus | | |
| | | | | |
| | |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>| |
| | | | | |
| | |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------| |
| | Create new device on in ishtp bus | | |
| | | | | |
| | |--Repeat HOST_CLIENT_PROPERTIES_REQ_CMD-till last one--| |
| | | | | |
| probed() |
| |----ishtp_cl_connect--->|----------------- CLIENT_CONNECT_REQ_CMD-------------->| |
| | | | | |
| | |<----------------CLIENT_CONNECT_RES_CMD----------------| |
| | | | | |
| |register event callback | | | |
| | | | | |
| |ishtp_cl_send( |
| HOSTIF_DM_ENUM_DEVICES) |----------fill ishtp_msg_hdr struct write to HW----- >| |
| | | | | |
| | | |<-----IRQ(IPC_PROTOCOL_ISHTP---| |
| | | | | |
| |<--ENUM_DEVICE RSP------| | | |
| | | | | |
| for each enumerated device |
| |ishtp_cl_send( |
| HOSTIF_GET_HID_DESCRIPTOR|----------fill ishtp_msg_hdr struct write to HW----- >| |
| | | | | |
| ...Response |
| | | | | |
| for each enumerated device |
| |ishtp_cl_send( |
| HOSTIF_GET_REPORT_DESCRIPTOR|--------------fill ishtp_msg_hdr struct write to HW-- >| |
| | | | | |
| | | | | |
| hid_allocate_device |
| | | | | |
| hid_add_device | | | |
| | | | | |
| |
| |
| 3.7 ISH Debugging |
| ----------------- |
| |
| To debug ISH, event tracing mechanism is used. To enable debug logs:: |
| |
| echo 1 > /sys/kernel/tracing/events/intel_ish/enable |
| cat /sys/kernel/tracing/trace |
| |
| 3.8 ISH IIO sysfs Example on Lenovo thinkpad Yoga 260 |
| ----------------------------------------------------- |
| |
| :: |
| |
| root@otcpl-ThinkPad-Yoga-260:~# tree -l /sys/bus/iio/devices/ |
| /sys/bus/iio/devices/ |
| ├── iio:device0 -> ../../../devices/0044:8086:22D8.0001/HID-SENSOR-200073.9.auto/iio:device0 |
| │ ├── buffer |
| │ │ ├── enable |
| │ │ ├── length |
| │ │ └── watermark |
| ... |
| │ ├── in_accel_hysteresis |
| │ ├── in_accel_offset |
| │ ├── in_accel_sampling_frequency |
| │ ├── in_accel_scale |
| │ ├── in_accel_x_raw |
| │ ├── in_accel_y_raw |
| │ ├── in_accel_z_raw |
| │ ├── name |
| │ ├── scan_elements |
| │ │ ├── in_accel_x_en |
| │ │ ├── in_accel_x_index |
| │ │ ├── in_accel_x_type |
| │ │ ├── in_accel_y_en |
| │ │ ├── in_accel_y_index |
| │ │ ├── in_accel_y_type |
| │ │ ├── in_accel_z_en |
| │ │ ├── in_accel_z_index |
| │ │ └── in_accel_z_type |
| ... |
| │ │ ├── devices |
| │ │ │ │ ├── buffer |
| │ │ │ │ │ ├── enable |
| │ │ │ │ │ ├── length |
| │ │ │ │ │ └── watermark |
| │ │ │ │ ├── dev |
| │ │ │ │ ├── in_intensity_both_raw |
| │ │ │ │ ├── in_intensity_hysteresis |
| │ │ │ │ ├── in_intensity_offset |
| │ │ │ │ ├── in_intensity_sampling_frequency |
| │ │ │ │ ├── in_intensity_scale |
| │ │ │ │ ├── name |
| │ │ │ │ ├── scan_elements |
| │ │ │ │ │ ├── in_intensity_both_en |
| │ │ │ │ │ ├── in_intensity_both_index |
| │ │ │ │ │ └── in_intensity_both_type |
| │ │ │ │ ├── trigger |
| │ │ │ │ │ └── current_trigger |
| ... |
| │ │ │ │ ├── buffer |
| │ │ │ │ │ ├── enable |
| │ │ │ │ │ ├── length |
| │ │ │ │ │ └── watermark |
| │ │ │ │ ├── dev |
| │ │ │ │ ├── in_magn_hysteresis |
| │ │ │ │ ├── in_magn_offset |
| │ │ │ │ ├── in_magn_sampling_frequency |
| │ │ │ │ ├── in_magn_scale |
| │ │ │ │ ├── in_magn_x_raw |
| │ │ │ │ ├── in_magn_y_raw |
| │ │ │ │ ├── in_magn_z_raw |
| │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_raw |
| │ │ │ │ ├── in_rot_hysteresis |
| │ │ │ │ ├── in_rot_offset |
| │ │ │ │ ├── in_rot_sampling_frequency |
| │ │ │ │ ├── in_rot_scale |
| │ │ │ │ ├── name |
| ... |
| │ │ │ │ ├── scan_elements |
| │ │ │ │ │ ├── in_magn_x_en |
| │ │ │ │ │ ├── in_magn_x_index |
| │ │ │ │ │ ├── in_magn_x_type |
| │ │ │ │ │ ├── in_magn_y_en |
| │ │ │ │ │ ├── in_magn_y_index |
| │ │ │ │ │ ├── in_magn_y_type |
| │ │ │ │ │ ├── in_magn_z_en |
| │ │ │ │ │ ├── in_magn_z_index |
| │ │ │ │ │ ├── in_magn_z_type |
| │ │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_en |
| │ │ │ │ │ ├── in_rot_from_north_magnetic_tilt_comp_index |
| │ │ │ │ │ └── in_rot_from_north_magnetic_tilt_comp_type |
| │ │ │ │ ├── trigger |
| │ │ │ │ │ └── current_trigger |
| ... |
| │ │ │ │ ├── buffer |
| │ │ │ │ │ ├── enable |
| │ │ │ │ │ ├── length |
| │ │ │ │ │ └── watermark |
| │ │ │ │ ├── dev |
| │ │ │ │ ├── in_anglvel_hysteresis |
| │ │ │ │ ├── in_anglvel_offset |
| │ │ │ │ ├── in_anglvel_sampling_frequency |
| │ │ │ │ ├── in_anglvel_scale |
| │ │ │ │ ├── in_anglvel_x_raw |
| │ │ │ │ ├── in_anglvel_y_raw |
| │ │ │ │ ├── in_anglvel_z_raw |
| │ │ │ │ ├── name |
| │ │ │ │ ├── scan_elements |
| │ │ │ │ │ ├── in_anglvel_x_en |
| │ │ │ │ │ ├── in_anglvel_x_index |
| │ │ │ │ │ ├── in_anglvel_x_type |
| │ │ │ │ │ ├── in_anglvel_y_en |
| │ │ │ │ │ ├── in_anglvel_y_index |
| │ │ │ │ │ ├── in_anglvel_y_type |
| │ │ │ │ │ ├── in_anglvel_z_en |
| │ │ │ │ │ ├── in_anglvel_z_index |
| │ │ │ │ │ └── in_anglvel_z_type |
| │ │ │ │ ├── trigger |
| │ │ │ │ │ └── current_trigger |
| ... |
| │ │ │ │ ├── buffer |
| │ │ │ │ │ ├── enable |
| │ │ │ │ │ ├── length |
| │ │ │ │ │ └── watermark |
| │ │ │ │ ├── dev |
| │ │ │ │ ├── in_anglvel_hysteresis |
| │ │ │ │ ├── in_anglvel_offset |
| │ │ │ │ ├── in_anglvel_sampling_frequency |
| │ │ │ │ ├── in_anglvel_scale |
| │ │ │ │ ├── in_anglvel_x_raw |
| │ │ │ │ ├── in_anglvel_y_raw |
| │ │ │ │ ├── in_anglvel_z_raw |
| │ │ │ │ ├── name |
| │ │ │ │ ├── scan_elements |
| │ │ │ │ │ ├── in_anglvel_x_en |
| │ │ │ │ │ ├── in_anglvel_x_index |
| │ │ │ │ │ ├── in_anglvel_x_type |
| │ │ │ │ │ ├── in_anglvel_y_en |
| │ │ │ │ │ ├── in_anglvel_y_index |
| │ │ │ │ │ ├── in_anglvel_y_type |
| │ │ │ │ │ ├── in_anglvel_z_en |
| │ │ │ │ │ ├── in_anglvel_z_index |
| │ │ │ │ │ └── in_anglvel_z_type |
| │ │ │ │ ├── trigger |
| │ │ │ │ │ └── current_trigger |
| ... |
