Commit b2eafd72 authored by Srinivas Pandruvada's avatar Srinivas Pandruvada Committed by Jiri Kosina

HID: sensor: Update document for custom sensor

Added custom sensor documentation
Signed-off-by: default avatarSrinivas Pandruvada <>
Acked-by: default avatarJonathan Cameron <>
Signed-off-by: default avatarJiri Kosina <>
parent 4a7de051
......@@ -138,3 +138,87 @@ accelerometer wants to poll X axis value, then it can call this function with
the usage id of X axis. HID sensors can provide events, so this is not necessary
to poll for any field. If there is some new sample, the core driver will call
registered callback function to process the sample.
HID Custom and generic Sensors
HID Sensor specification defines two special sensor usage types. Since they
don't represent a standard sensor, it is not possible to define using Linux IIO
type interfaces.
The purpose of these sensors is to extend the functionality or provide a
way to obfuscate the data being communicated by a sensor. Without knowing the
mapping between the data and its encapsulated form, it is difficult for
an application/driver to determine what data is being communicated by the sensor.
This allows some differentiating use cases, where vendor can provide applications.
Some common use cases are debug other sensors or to provide some events like
keyboard attached/detached or lid open/close.
To allow application to utilize these sensors, here they are exported uses sysfs
attribute groups, attributes and misc device interface.
An example of this representation on sysfs:
/sys/devices/pci0000:00/INT33C2:00/i2c-0/i2c-INT33D1:00/0018:8086:09FA.0001/$ tree -R
????????? enable_sensor
????????? feature-0-200316
??????? ????????? feature-0-200316-maximum
??????? ????????? feature-0-200316-minimum
??????? ????????? feature-0-200316-name
??????? ????????? feature-0-200316-size
??????? ????????? feature-0-200316-unit-expo
??????? ????????? feature-0-200316-units
??????? ????????? feature-0-200316-value
????????? feature-1-200201
??????? ????????? feature-1-200201-maximum
??????? ????????? feature-1-200201-minimum
??????? ????????? feature-1-200201-name
??????? ????????? feature-1-200201-size
??????? ????????? feature-1-200201-unit-expo
??????? ????????? feature-1-200201-units
??????? ????????? feature-1-200201-value
????????? input-0-200201
??????? ????????? input-0-200201-maximum
??????? ????????? input-0-200201-minimum
??????? ????????? input-0-200201-name
??????? ????????? input-0-200201-size
??????? ????????? input-0-200201-unit-expo
??????? ????????? input-0-200201-units
??????? ????????? input-0-200201-value
????????? input-1-200202
??????? ????????? input-1-200202-maximum
??????? ????????? input-1-200202-minimum
??????? ????????? input-1-200202-name
??????? ????????? input-1-200202-size
??????? ????????? input-1-200202-unit-expo
??????? ????????? input-1-200202-units
??????? ????????? input-1-200202-value
Here there is a custom sensors with four fields, two feature and two inputs.
Each field is represented by a set of attributes. All fields except the "value"
are read only. The value field is a RW field.
/sys/bus/platform/devices/$ grep -r . *
How to enable such sensor?
By default sensor can be power gated. To enable sysfs attribute "enable" can be
$ echo 1 > enable_sensor
Once enabled and powered on, sensor can report value using HID reports.
These reports are pushed using misc device interface in a FIFO order.
/dev$ tree | grep
??????? ????????? 10:53 -> ../
Each reports can be of variable length preceded by a header. This header
consist of a 32 bit usage id, 64 bit time stamp and 32 bit length field of raw
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