225 lines
8.8 KiB
Plaintext
225 lines
8.8 KiB
Plaintext
|
|
HID Sensors Framework
|
|
======================
|
|
HID sensor framework provides necessary interfaces to implement sensor drivers,
|
|
which are connected to a sensor hub. The sensor hub is a HID device and it provides
|
|
a report descriptor conforming to HID 1.12 sensor usage tables.
|
|
|
|
Description from the HID 1.12 "HID Sensor Usages" specification:
|
|
"Standardization of HID usages for sensors would allow (but not require) sensor
|
|
hardware vendors to provide a consistent Plug And Play interface at the USB boundary,
|
|
thereby enabling some operating systems to incorporate common device drivers that
|
|
could be reused between vendors, alleviating any need for the vendors to provide
|
|
the drivers themselves."
|
|
|
|
This specification describes many usage IDs, which describe the type of sensor
|
|
and also the individual data fields. Each sensor can have variable number of
|
|
data fields. The length and order is specified in the report descriptor. For
|
|
example a part of report descriptor can look like:
|
|
|
|
INPUT(1)[INPUT]
|
|
..
|
|
Field(2)
|
|
Physical(0020.0073)
|
|
Usage(1)
|
|
0020.045f
|
|
Logical Minimum(-32767)
|
|
Logical Maximum(32767)
|
|
Report Size(8)
|
|
Report Count(1)
|
|
Report Offset(16)
|
|
Flags(Variable Absolute)
|
|
..
|
|
..
|
|
|
|
The report is indicating "sensor page (0x20)" contains an accelerometer-3D (0x73).
|
|
This accelerometer-3D has some fields. Here for example field 2 is motion intensity
|
|
(0x045f) with a logical minimum value of -32767 and logical maximum of 32767. The
|
|
order of fields and length of each field is important as the input event raw
|
|
data will use this format.
|
|
|
|
|
|
Implementation
|
|
=================
|
|
|
|
This specification defines many different types of sensors with different sets of
|
|
data fields. It is difficult to have a common input event to user space applications,
|
|
for different sensors. For example an accelerometer can send X,Y and Z data, whereas
|
|
an ambient light sensor can send illumination data.
|
|
So the implementation has two parts:
|
|
- Core hid driver
|
|
- Individual sensor processing part (sensor drivers)
|
|
|
|
Core driver
|
|
-----------
|
|
The core driver registers (hid-sensor-hub) registers as a HID driver. It parses
|
|
report descriptors and identifies all the sensors present. It adds an MFD device
|
|
with name HID-SENSOR-xxxx (where xxxx is usage id from the specification).
|
|
For example
|
|
HID-SENSOR-200073 is registered for an Accelerometer 3D driver.
|
|
So if any driver with this name is inserted, then the probe routine for that
|
|
function will be called. So an accelerometer processing driver can register
|
|
with this name and will be probed if there is an accelerometer-3D detected.
|
|
|
|
The core driver provides a set of APIs which can be used by the processing
|
|
drivers to register and get events for that usage id. Also it provides parsing
|
|
functions, which get and set each input/feature/output report.
|
|
|
|
Individual sensor processing part (sensor drivers)
|
|
-----------
|
|
The processing driver will use an interface provided by the core driver to parse
|
|
the report and get the indexes of the fields and also can get events. This driver
|
|
can use IIO interface to use the standard ABI defined for a type of sensor.
|
|
|
|
|
|
Core driver Interface
|
|
=====================
|
|
|
|
Callback structure:
|
|
Each processing driver can use this structure to set some callbacks.
|
|
int (*suspend)(..): Callback when HID suspend is received
|
|
int (*resume)(..): Callback when HID resume is received
|
|
int (*capture_sample)(..): Capture a sample for one of its data fields
|
|
int (*send_event)(..): One complete event is received which can have
|
|
multiple data fields.
|
|
|
|
Registration functions:
|
|
int sensor_hub_register_callback(struct hid_sensor_hub_device *hsdev,
|
|
u32 usage_id,
|
|
struct hid_sensor_hub_callbacks *usage_callback):
|
|
|
|
Registers callbacks for an usage id. The callback functions are not allowed
|
|
to sleep.
|
|
|
|
|
|
int sensor_hub_remove_callback(struct hid_sensor_hub_device *hsdev,
|
|
u32 usage_id):
|
|
|
|
Removes callbacks for an usage id.
|
|
|
|
|
|
Parsing function:
|
|
int sensor_hub_input_get_attribute_info(struct hid_sensor_hub_device *hsdev,
|
|
u8 type,
|
|
u32 usage_id, u32 attr_usage_id,
|
|
struct hid_sensor_hub_attribute_info *info);
|
|
|
|
A processing driver can look for some field of interest and check if it exists
|
|
in a report descriptor. If it exists it will store necessary information
|
|
so that fields can be set or get individually.
|
|
These indexes avoid searching every time and getting field index to get or set.
|
|
|
|
|
|
Set Feature report
|
|
int sensor_hub_set_feature(struct hid_sensor_hub_device *hsdev, u32 report_id,
|
|
u32 field_index, s32 value);
|
|
|
|
This interface is used to set a value for a field in feature report. For example
|
|
if there is a field report_interval, which is parsed by a call to
|
|
sensor_hub_input_get_attribute_info before, then it can directly set that individual
|
|
field.
|
|
|
|
|
|
int sensor_hub_get_feature(struct hid_sensor_hub_device *hsdev, u32 report_id,
|
|
u32 field_index, s32 *value);
|
|
|
|
This interface is used to get a value for a field in input report. For example
|
|
if there is a field report_interval, which is parsed by a call to
|
|
sensor_hub_input_get_attribute_info before, then it can directly get that individual
|
|
field value.
|
|
|
|
|
|
int sensor_hub_input_attr_get_raw_value(struct hid_sensor_hub_device *hsdev,
|
|
u32 usage_id,
|
|
u32 attr_usage_id, u32 report_id);
|
|
|
|
This is used to get a particular field value through input reports. For example
|
|
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/HID-SENSOR-2000e1.6.auto$ 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.
|
|
Example
|
|
/sys/bus/platform/devices/HID-SENSOR-2000e1.6.auto/feature-0-200316$ grep -r . *
|
|
feature-0-200316-maximum:6
|
|
feature-0-200316-minimum:0
|
|
feature-0-200316-name:property-reporting-state
|
|
feature-0-200316-size:1
|
|
feature-0-200316-unit-expo:0
|
|
feature-0-200316-units:25
|
|
feature-0-200316-value:1
|
|
|
|
How to enable such sensor?
|
|
By default sensor can be power gated. To enable sysfs attribute "enable" can be
|
|
used.
|
|
$ 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 HID-SENSOR-2000e1.6.auto
|
|
??????? ????????? 10:53 -> ../HID-SENSOR-2000e1.6.auto
|
|
????????? HID-SENSOR-2000e1.6.auto
|
|
|
|
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
|
|
data.
|