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Documentation: HID: intel-ish-hid editing & corrections
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Do basic editing & correction to intel-ish-hid.rst:
- fix grammar, verb tense, punctutation, and word phrasing
- fix spellos
- hyphenate multi-word adjectives
- collapse 2 spaces to one space in the middle of sentences
- use "I2C" instead of lower-case letters (as Linux I2C does)
- change space indentation to tab
- use HID instead of hid consistently
- use a list so that some line items do not run together
- use "a UUID" instead of "an UUID"

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: linux-input@vger.kernel.org
Cc: linux-iio@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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rddunlap authored and Jiri Kosina committed Jan 4, 2021
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78 changes: 40 additions & 38 deletions Documentation/hid/intel-ish-hid.rst
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Expand Up @@ -4,19 +4,19 @@ 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
processor to go into low power modes more often, resulting in 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.
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
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.
mainly use HID over I2C or USB. But ISH doesn't use either I2C or USB.

1. Overview
===========
Expand All @@ -35,7 +35,7 @@ for a very high speed communication::
----------------- ----------------------
PCI PCI
----------------- ----------------------
|Host controller| --> | ISH processor |
|Host controller| --> | ISH processor |
----------------- ----------------------
USB Link
----------------- ----------------------
Expand All @@ -50,13 +50,13 @@ 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.
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 HID driver) identifies the device type and registers with the HID core.

2. ISH Implementation: Block Diagram
====================================
Expand Down Expand Up @@ -104,49 +104,50 @@ is registered as a device on this bus. The driver, which binds each device

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
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 used memory mapped I/O. The registers are defined in
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 other messages
are to and from transport layers.
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 FW.
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 door bell mechanism is used in messaging to trigger processing in host and
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.
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.
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.
Refer to struct ishtp_hw_ops for callbacks.

3.3 ISH Transport layer
-----------------------
Expand All @@ -158,7 +159,7 @@ Location: drivers/hid/intel-ish-hid/ishtp/

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
(see ishtp/hbm.h for details)
- A flow control mechanism to avoid buffer overflows

This protocol resembles bus messages described in the following document:
Expand All @@ -168,14 +169,14 @@ 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
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 sent a message, it may not send another one
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.
Expand Down Expand Up @@ -209,7 +210,7 @@ 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
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.
Expand All @@ -219,8 +220,8 @@ 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
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
Expand All @@ -230,10 +231,10 @@ 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.
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 in implantation and allow independent driver handle each client
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).

Expand Down Expand Up @@ -270,7 +271,7 @@ The ISHTP client driver is responsible for:
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
Documentation/ABI/testing/sysfs-bus-iio for IIO ABIs to user space.

3.6 End to End HID transport Sequence Diagram
---------------------------------------------
Expand Down Expand Up @@ -341,9 +342,10 @@ Documentation/ABI/testing/sysfs-bus-iio for IIO ABIs to user space
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
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
-----------------------------------------------------
Expand Down

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