Document explaining ISH HID operation and implementation. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx> --- Documentation/hid/intel-ish-hid.txt | 454 ++++++++++++++++++++++++++++++++++++ 1 file changed, 454 insertions(+) create mode 100644 Documentation/hid/intel-ish-hid.txt diff --git a/Documentation/hid/intel-ish-hid.txt b/Documentation/hid/intel-ish-hid.txt new file mode 100644 index 0000000..d48b21c --- /dev/null +++ b/Documentation/hid/intel-ish-hid.txt @@ -0,0 +1,454 @@ +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 the increased +battery life. + +There are many vendors providing external sensor hubs confirming to HID +Sensor usage tables, and used in several tablets, 2 in 1 convertible laptops +and embedded products. Linux 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 application or senor firmware +update application. + +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 enumerate 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 used 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 other messages +are 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 FW. +Optionally the caller can register handler to get notification of completion. +A door bell 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 are 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 +(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 an 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 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 thw 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 +needs 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 initiate a connection, a ring or RX and TX buffers are allocated. +The size of ring can be specified by the client. HID client set 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 allow discovery of clients present in the FW. +There can be multiple sensor clients and clients for calibration function. + +To ease in implantation and allow independent driver handle each client +this transport layer takes advantage of Linux Bus driver model. Each +client is registered as device on the 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.txt 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/debug/tracing/events/intel_ish/enable +cat sys/kernel/debug/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 +... -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
