linux/Documentation/misc-devices/lis3lv02d
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   1Kernel driver lis3lv02d
   2=======================
   3
   4Supported chips:
   5
   6  * STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision)
   7  * STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits)
   8
   9Authors:
  10        Yan Burman <burman.yan@gmail.com>
  11        Eric Piel <eric.piel@tremplin-utc.net>
  12
  13
  14Description
  15-----------
  16
  17This driver provides support for the accelerometer found in various HP laptops
  18sporting the feature officially called "HP Mobile Data Protection System 3D" or
  19"HP 3D DriveGuard". It detects automatically laptops with this sensor. Known
  20models (full list can be found in drivers/platform/x86/hp_accel.c) will have
  21their axis automatically oriented on standard way (eg: you can directly play
  22neverball). The accelerometer data is readable via
  23/sys/devices/platform/lis3lv02d. Reported values are scaled
  24to mg values (1/1000th of earth gravity).
  25
  26Sysfs attributes under /sys/devices/platform/lis3lv02d/:
  27position - 3D position that the accelerometer reports. Format: "(x,y,z)"
  28rate - read reports the sampling rate of the accelerometer device in HZ.
  29        write changes sampling rate of the accelerometer device.
  30        Only values which are supported by HW are accepted.
  31selftest - performs selftest for the chip as specified by chip manufacturer.
  32
  33This driver also provides an absolute input class device, allowing
  34the laptop to act as a pinball machine-esque joystick. Joystick device can be
  35calibrated. Joystick device can be in two different modes.
  36By default output values are scaled between -32768 .. 32767. In joystick raw
  37mode, joystick and sysfs position entry have the same scale. There can be
  38small difference due to input system fuzziness feature.
  39Events are also available as input event device.
  40
  41Selftest is meant only for hardware diagnostic purposes. It is not meant to be
  42used during normal operations. Position data is not corrupted during selftest
  43but interrupt behaviour is not guaranteed to work reliably. In test mode, the
  44sensing element is internally moved little bit. Selftest measures difference
  45between normal mode and test mode. Chip specifications tell the acceptance
  46limit for each type of the chip. Limits are provided via platform data
  47to allow adjustment of the limits without a change to the actual driver.
  48Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are
  49measured difference between modes. Axes are not remapped in selftest mode.
  50Measurement values are provided to help HW diagnostic applications to make
  51final decision.
  52
  53On HP laptops, if the led infrastructure is activated, support for a led
  54indicating disk protection will be provided as /sys/class/leds/hp::hddprotect.
  55
  56Another feature of the driver is misc device called "freefall" that
  57acts similar to /dev/rtc and reacts on free-fall interrupts received
  58from the device. It supports blocking operations, poll/select and
  59fasync operation modes. You must read 1 bytes from the device.  The
  60result is number of free-fall interrupts since the last successful
  61read (or 255 if number of interrupts would not fit). See the hpfall.c
  62file for an example on using the device.
  63
  64
  65Axes orientation
  66----------------
  67
  68For better compatibility between the various laptops. The values reported by
  69the accelerometer are converted into a "standard" organisation of the axes
  70(aka "can play neverball out of the box"):
  71 * When the laptop is horizontal the position reported is about 0 for X and Y
  72        and a positive value for Z
  73 * If the left side is elevated, X increases (becomes positive)
  74 * If the front side (where the touchpad is) is elevated, Y decreases
  75        (becomes negative)
  76 * If the laptop is put upside-down, Z becomes negative
  77
  78If your laptop model is not recognized (cf "dmesg"), you can send an
  79email to the maintainer to add it to the database.  When reporting a new
  80laptop, please include the output of "dmidecode" plus the value of
  81/sys/devices/platform/lis3lv02d/position in these four cases.
  82
  83Q&A
  84---
  85
  86Q: How do I safely simulate freefall? I have an HP "portable
  87workstation" which has about 3.5kg and a plastic case, so letting it
  88fall to the ground is out of question...
  89
  90A: The sensor is pretty sensitive, so your hands can do it. Lift it
  91into free space, follow the fall with your hands for like 10
  92centimeters. That should be enough to trigger the detection.
  93
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