Documentation/input/devices/alps.rst

Source file repositories/reference/linux-study-clean/Documentation/input/devices/alps.rst

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Documentation/input/devices/alps.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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ALPS Touchpad Protocol
----------------------

Introduction
------------
Currently the ALPS touchpad driver supports seven protocol versions in use by
ALPS touchpads, called versions 1, 2, 3, 4, 5, 6, 7 and 8.

Since roughly mid-2010 several new ALPS touchpads have been released and
integrated into a variety of laptops and netbooks.  These new touchpads
have enough behavior differences that the alps_model_data definition
table, describing the properties of the different versions, is no longer
adequate.  The design choices were to re-define the alps_model_data
table, with the risk of regression testing existing devices, or isolate
the new devices outside of the alps_model_data table.  The latter design
choice was made.  The new touchpad signatures are named: "Rushmore",
"Pinnacle", and "Dolphin", which you will see in the alps.c code.
For the purposes of this document, this group of ALPS touchpads will
generically be called "new ALPS touchpads".

We experimented with probing the ACPI interface _HID (Hardware ID)/_CID
(Compatibility ID) definition as a way to uniquely identify the
different ALPS variants but there did not appear to be a 1:1 mapping.
In fact, it appeared to be an m:n mapping between the _HID and actual
hardware type.

Detection
---------

All ALPS touchpads should respond to the "E6 report" command sequence:
E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or
00-00-64 if no buttons are pressed. The bits 0-2 of the first byte will be 1s
if some buttons are pressed.

If the E6 report is successful, the touchpad model is identified using the "E7
report" sequence: E8-E7-E7-E7-E9. The response is the model signature and is
matched against known models in the alps_model_data_array.

For older touchpads supporting protocol versions 3 and 4, the E7 report
model signature is always 73-02-64. To differentiate between these
versions, the response from the "Enter Command Mode" sequence must be
inspected as described below.

The new ALPS touchpads have an E7 signature of 73-03-50 or 73-03-0A but
seem to be better differentiated by the EC Command Mode response.

Command Mode
------------

Protocol versions 3 and 4 have a command mode that is used to read and write
one-byte device registers in a 16-bit address space. The command sequence
EC-EC-EC-E9 places the device in command mode, and the device will respond
with 88-07 followed by a third byte. This third byte can be used to determine
whether the devices uses the version 3 or 4 protocol.

To exit command mode, PSMOUSE_CMD_SETSTREAM (EA) is sent to the touchpad.

While in command mode, register addresses can be set by first sending a
specific command, either EC for v3 devices or F5 for v4 devices. Then the
address is sent one nibble at a time, where each nibble is encoded as a
command with optional data. This encoding differs slightly between the v3 and
v4 protocols.

Once an address has been set, the addressed register can be read by sending
PSMOUSE_CMD_GETINFO (E9). The first two bytes of the response contains the
address of the register being read, and the third contains the value of the
register. Registers are written by writing the value one nibble at a time
using the same encoding used for addresses.

Annotation

Implementation Notes