1=======================
2Kernel driver lis3lv02d
3=======================
4
5Supported chips:
6
7  * STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision)
8  * STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits) and
9    LIS331DLH (16 bits)
10
11Authors:
12        - Yan Burman <burman.yan@gmail.com>
13	- Eric Piel <eric.piel@tremplin-utc.net>
14
15
16Description
17-----------
18
19This driver provides support for the accelerometer found in various HP laptops
20sporting the feature officially called "HP Mobile Data Protection System 3D" or
21"HP 3D DriveGuard". It detects automatically laptops with this sensor. Known
22models (full list can be found in drivers/platform/x86/hp_accel.c) will have
23their axis automatically oriented on standard way (eg: you can directly play
24neverball). The accelerometer data is readable via
25/sys/devices/platform/lis3lv02d. Reported values are scaled
26to mg values (1/1000th of earth gravity).
27
28Sysfs attributes under /sys/devices/platform/lis3lv02d/:
29
30position
31      - 3D position that the accelerometer reports. Format: "(x,y,z)"
32rate
33      - read reports the sampling rate of the accelerometer device in HZ.
34	write changes sampling rate of the accelerometer device.
35	Only values which are supported by HW are accepted.
36selftest
37      - performs selftest for the chip as specified by chip manufacturer.
38
39This driver also provides an absolute input class device, allowing
40the laptop to act as a pinball machine-esque joystick. Joystick device can be
41calibrated. Joystick device can be in two different modes.
42By default output values are scaled between -32768 .. 32767. In joystick raw
43mode, joystick and sysfs position entry have the same scale. There can be
44small difference due to input system fuzziness feature.
45Events are also available as input event device.
46
47Selftest is meant only for hardware diagnostic purposes. It is not meant to be
48used during normal operations. Position data is not corrupted during selftest
49but interrupt behaviour is not guaranteed to work reliably. In test mode, the
50sensing element is internally moved little bit. Selftest measures difference
51between normal mode and test mode. Chip specifications tell the acceptance
52limit for each type of the chip. Limits are provided via platform data
53to allow adjustment of the limits without a change to the actual driver.
54Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are
55measured difference between modes. Axes are not remapped in selftest mode.
56Measurement values are provided to help HW diagnostic applications to make
57final decision.
58
59On HP laptops, if the led infrastructure is activated, support for a led
60indicating disk protection will be provided as /sys/class/leds/hp::hddprotect.
61
62Another feature of the driver is misc device called "freefall" that
63acts similar to /dev/rtc and reacts on free-fall interrupts received
64from the device. It supports blocking operations, poll/select and
65fasync operation modes. You must read 1 bytes from the device.  The
66result is number of free-fall interrupts since the last successful
67read (or 255 if number of interrupts would not fit). See the freefall.c
68file for an example on using the device.
69
70
71Axes orientation
72----------------
73
74For better compatibility between the various laptops. The values reported by
75the accelerometer are converted into a "standard" organisation of the axes
76(aka "can play neverball out of the box"):
77
78 * When the laptop is horizontal the position reported is about 0 for X and Y
79   and a positive value for Z
80 * If the left side is elevated, X increases (becomes positive)
81 * If the front side (where the touchpad is) is elevated, Y decreases
82   (becomes negative)
83 * If the laptop is put upside-down, Z becomes negative
84
85If your laptop model is not recognized (cf "dmesg"), you can send an
86email to the maintainer to add it to the database.  When reporting a new
87laptop, please include the output of "dmidecode" plus the value of
88/sys/devices/platform/lis3lv02d/position in these four cases.
89
90Q&A
91---
92
93Q: How do I safely simulate freefall? I have an HP "portable
94workstation" which has about 3.5kg and a plastic case, so letting it
95fall to the ground is out of question...
96
97A: The sensor is pretty sensitive, so your hands can do it. Lift it
98into free space, follow the fall with your hands for like 10
99centimeters. That should be enough to trigger the detection.
100