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455fbdd3 | 1 | Kernel driver lis3lv02d |
2b872903 | 2 | ======================= |
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3 | |
4 | Supported chips: | |
5 | ||
bc62c147 | 6 | * STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision) |
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7 | * STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits) and |
8 | LIS331DLH (16 bits) | |
455fbdd3 | 9 | |
2b872903 | 10 | Authors: |
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11 | Yan Burman <burman.yan@gmail.com> |
12 | Eric Piel <eric.piel@tremplin-utc.net> | |
13 | ||
14 | ||
15 | Description | |
16 | ----------- | |
17 | ||
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18 | This driver provides support for the accelerometer found in various HP laptops |
19 | sporting the feature officially called "HP Mobile Data Protection System 3D" or | |
20 | "HP 3D DriveGuard". It detects automatically laptops with this sensor. Known | |
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21 | models (full list can be found in drivers/platform/x86/hp_accel.c) will have |
22 | their axis automatically oriented on standard way (eg: you can directly play | |
bc62c147 | 23 | neverball). The accelerometer data is readable via |
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24 | /sys/devices/platform/lis3lv02d. Reported values are scaled |
25 | to mg values (1/1000th of earth gravity). | |
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26 | |
27 | Sysfs attributes under /sys/devices/platform/lis3lv02d/: | |
28 | position - 3D position that the accelerometer reports. Format: "(x,y,z)" | |
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29 | rate - read reports the sampling rate of the accelerometer device in HZ. |
30 | write changes sampling rate of the accelerometer device. | |
31 | Only values which are supported by HW are accepted. | |
32 | selftest - performs selftest for the chip as specified by chip manufacturer. | |
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33 | |
34 | This driver also provides an absolute input class device, allowing | |
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35 | the laptop to act as a pinball machine-esque joystick. Joystick device can be |
36 | calibrated. Joystick device can be in two different modes. | |
37 | By default output values are scaled between -32768 .. 32767. In joystick raw | |
38 | mode, joystick and sysfs position entry have the same scale. There can be | |
39 | small difference due to input system fuzziness feature. | |
40 | Events are also available as input event device. | |
41 | ||
42 | Selftest is meant only for hardware diagnostic purposes. It is not meant to be | |
43 | used during normal operations. Position data is not corrupted during selftest | |
44 | but interrupt behaviour is not guaranteed to work reliably. In test mode, the | |
45 | sensing element is internally moved little bit. Selftest measures difference | |
46 | between normal mode and test mode. Chip specifications tell the acceptance | |
47 | limit for each type of the chip. Limits are provided via platform data | |
48 | to allow adjustment of the limits without a change to the actual driver. | |
49 | Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are | |
50 | measured difference between modes. Axes are not remapped in selftest mode. | |
51 | Measurement values are provided to help HW diagnostic applications to make | |
52 | final decision. | |
455fbdd3 | 53 | |
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54 | On HP laptops, if the led infrastructure is activated, support for a led |
55 | indicating disk protection will be provided as /sys/class/leds/hp::hddprotect. | |
56 | ||
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57 | Another feature of the driver is misc device called "freefall" that |
58 | acts similar to /dev/rtc and reacts on free-fall interrupts received | |
59 | from the device. It supports blocking operations, poll/select and | |
60 | fasync operation modes. You must read 1 bytes from the device. The | |
61 | result is number of free-fall interrupts since the last successful | |
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62 | read (or 255 if number of interrupts would not fit). See the hpfall.c |
63 | file for an example on using the device. | |
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64 | |
65 | ||
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66 | Axes orientation |
67 | ---------------- | |
68 | ||
69 | For better compatibility between the various laptops. The values reported by | |
70 | the accelerometer are converted into a "standard" organisation of the axes | |
71 | (aka "can play neverball out of the box"): | |
72 | * When the laptop is horizontal the position reported is about 0 for X and Y | |
2b872903 | 73 | and a positive value for Z |
455fbdd3 | 74 | * If the left side is elevated, X increases (becomes positive) |
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75 | * If the front side (where the touchpad is) is elevated, Y decreases |
76 | (becomes negative) | |
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77 | * If the laptop is put upside-down, Z becomes negative |
78 | ||
219beb29 | 79 | If your laptop model is not recognized (cf "dmesg"), you can send an |
bc62c147 | 80 | email to the maintainer to add it to the database. When reporting a new |
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81 | laptop, please include the output of "dmidecode" plus the value of |
82 | /sys/devices/platform/lis3lv02d/position in these four cases. | |
455fbdd3 | 83 | |
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84 | Q&A |
85 | --- | |
86 | ||
87 | Q: How do I safely simulate freefall? I have an HP "portable | |
88 | workstation" which has about 3.5kg and a plastic case, so letting it | |
89 | fall to the ground is out of question... | |
90 | ||
91 | A: The sensor is pretty sensitive, so your hands can do it. Lift it | |
92 | into free space, follow the fall with your hands for like 10 | |
93 | centimeters. That should be enough to trigger the detection. |