Documentation/hid/intel-ish-hid.rst

Source file repositories/reference/linux-study-clean/Documentation/hid/intel-ish-hid.rst

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Documentation/hid/intel-ish-hid.rst
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=================================
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.

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.

ISH Implementation: Block Diagram
=================================

::

	 ---------------------------
	|  User Space Applications  |
	 ---------------------------

  ----------------IIO ABI----------------

Annotation

Implementation Notes