On 07/04/2012 08:52 PM, srinivas pandruvada wrote: > Added a summary of HID sensor framework. > A nice description. One additional nitpick (I think) on top of Peters. (and mine really is a nitpick ;) > Signed-off-by: srinivas pandruvada <srinivas.pandruvada@xxxxxxxxx> > --- > Documentation/hid/hid-sensor.txt | 139 ++++++++++++++++++++++++++++++++++++++ > 1 files changed, 139 insertions(+), 0 deletions(-) > create mode 100755 Documentation/hid/hid-sensor.txt > > diff --git a/Documentation/hid/hid-sensor.txt b/Documentation/hid/hid-sensor.txt > new file mode 100755 > index 0000000..a4b565f > --- /dev/null > +++ b/Documentation/hid/hid-sensor.txt > @@ -0,0 +1,139 @@ > + > +HID Sensors Framework > +====================== > +HID sensor framework provides necessary interfaces to implement sensor drivers, > +which are connected to a sensor hub. The sensor hub is HID device and it provides > +a report descriptor confirming 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 and 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 set 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 is 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 a parsing > +functions, get and set each input/feature/output report. > + > +Individual sensor processing part (sensor drivers) > +----------- > +The processing driver will use interface provided by 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 field > + 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. > + > + > +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 the it will store necessary information > +so that that field 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); > + nitpick. Inconsistent blank lines (2 here, 1 in other similar loations). > + > +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. > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
