HID: sensor: Update document for custom sensor
Added custom sensor documentation Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Acked-by: Jonathan Cameron <jic23@kernel.org> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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@ -138,3 +138,87 @@ accelerometer wants to poll X axis value, then it can call this function with
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the usage id of X axis. HID sensors can provide events, so this is not necessary
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to poll for any field. If there is some new sample, the core driver will call
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registered callback function to process the sample.
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----------
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HID Custom and generic Sensors
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HID Sensor specification defines two special sensor usage types. Since they
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don't represent a standard sensor, it is not possible to define using Linux IIO
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type interfaces.
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The purpose of these sensors is to extend the functionality or provide a
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way to obfuscate the data being communicated by a sensor. Without knowing the
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mapping between the data and its encapsulated form, it is difficult for
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an application/driver to determine what data is being communicated by the sensor.
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This allows some differentiating use cases, where vendor can provide applications.
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Some common use cases are debug other sensors or to provide some events like
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keyboard attached/detached or lid open/close.
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To allow application to utilize these sensors, here they are exported uses sysfs
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attribute groups, attributes and misc device interface.
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An example of this representation on sysfs:
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/sys/devices/pci0000:00/INT33C2:00/i2c-0/i2c-INT33D1:00/0018:8086:09FA.0001/HID-SENSOR-2000e1.6.auto$ tree -R
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.
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????????? enable_sensor
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????????? feature-0-200316
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??????? ????????? feature-0-200316-maximum
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??????? ????????? feature-0-200316-minimum
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??????? ????????? feature-0-200316-name
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??????? ????????? feature-0-200316-size
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??????? ????????? feature-0-200316-unit-expo
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??????? ????????? feature-0-200316-units
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??????? ????????? feature-0-200316-value
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????????? feature-1-200201
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??????? ????????? feature-1-200201-maximum
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??????? ????????? feature-1-200201-minimum
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??????? ????????? feature-1-200201-name
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??????? ????????? feature-1-200201-size
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??????? ????????? feature-1-200201-unit-expo
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??????? ????????? feature-1-200201-units
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??????? ????????? feature-1-200201-value
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????????? input-0-200201
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??????? ????????? input-0-200201-maximum
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??????? ????????? input-0-200201-minimum
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??????? ????????? input-0-200201-name
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??????? ????????? input-0-200201-size
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??????? ????????? input-0-200201-unit-expo
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??????? ????????? input-0-200201-units
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??????? ????????? input-0-200201-value
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????????? input-1-200202
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??????? ????????? input-1-200202-maximum
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??????? ????????? input-1-200202-minimum
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??????? ????????? input-1-200202-name
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??????? ????????? input-1-200202-size
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??????? ????????? input-1-200202-unit-expo
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??????? ????????? input-1-200202-units
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??????? ????????? input-1-200202-value
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Here there is a custom sensors with four fields, two feature and two inputs.
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Each field is represented by a set of attributes. All fields except the "value"
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are read only. The value field is a RW field.
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Example
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/sys/bus/platform/devices/HID-SENSOR-2000e1.6.auto/feature-0-200316$ grep -r . *
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feature-0-200316-maximum:6
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feature-0-200316-minimum:0
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feature-0-200316-name:property-reporting-state
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feature-0-200316-size:1
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feature-0-200316-unit-expo:0
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feature-0-200316-units:25
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feature-0-200316-value:1
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How to enable such sensor?
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By default sensor can be power gated. To enable sysfs attribute "enable" can be
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used.
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$ echo 1 > enable_sensor
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Once enabled and powered on, sensor can report value using HID reports.
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These reports are pushed using misc device interface in a FIFO order.
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/dev$ tree | grep HID-SENSOR-2000e1.6.auto
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??????? ????????? 10:53 -> ../HID-SENSOR-2000e1.6.auto
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????????? HID-SENSOR-2000e1.6.auto
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Each reports can be of variable length preceded by a header. This header
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consist of a 32 bit usage id, 64 bit time stamp and 32 bit length field of raw
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data.
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