docs: hid: convert to ReST

Rename the HID documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

While here, fix the sysfs example from hid-sensor.txt, that
has a lot of "?" instead of the proper UTF-8 characters that
are produced by the tree command.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

1 files changed, 242 insertions, 0 deletions

diff --git a/Documentation/hid/hid-sensor.rst b/Documentation/hid/hid-sensor.rst
new file mode 100644
index 000000000000..758972e34971
--- /dev/null
+++ b/Documentation/hid/hid-sensor.rst
@@ -0,0 +1,242 @@
+=====================
+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.