1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ============================== 3 ==============================
4 Kernel driver for Qualcomm LPG 4 Kernel driver for Qualcomm LPG
5 ============================== 5 ==============================
6 6
7 Description 7 Description
8 ----------- 8 -----------
9 9
10 The Qualcomm LPG can be found in a variety of 10 The Qualcomm LPG can be found in a variety of Qualcomm PMICs and consists of a
11 number of PWM channels, a programmable pattern 11 number of PWM channels, a programmable pattern lookup table and a RGB LED
12 current sink. 12 current sink.
13 13
14 To facilitate the various use cases, the LPG c 14 To facilitate the various use cases, the LPG channels can be exposed as
15 individual LEDs, grouped together as RGB LEDs 15 individual LEDs, grouped together as RGB LEDs or otherwise be accessed as PWM
16 channels. The output of each PWM channel is ro 16 channels. The output of each PWM channel is routed to other hardware
17 blocks, such as the RGB current sink, GPIO pin 17 blocks, such as the RGB current sink, GPIO pins etc.
18 18
19 The each PWM channel can operate with a period 19 The each PWM channel can operate with a period between 27us and 384 seconds and
20 has a 9 bit resolution of the duty cycle. 20 has a 9 bit resolution of the duty cycle.
21 21
22 In order to provide support for status notific 22 In order to provide support for status notifications with the CPU subsystem in
23 deeper idle states the LPG provides pattern su 23 deeper idle states the LPG provides pattern support. This consists of a shared
24 lookup table of brightness values and per chan 24 lookup table of brightness values and per channel properties to select the
25 range within the table to use, the rate and if 25 range within the table to use, the rate and if the pattern should repeat.
26 26
27 The pattern for a channel can be programmed us 27 The pattern for a channel can be programmed using the "pattern" trigger, using
28 the hw_pattern attribute. 28 the hw_pattern attribute.
29 29
30 /sys/class/leds/<led>/hw_pattern 30 /sys/class/leds/<led>/hw_pattern
31 -------------------------------- 31 --------------------------------
32 32
33 Specify a hardware pattern for a Qualcomm LPG 33 Specify a hardware pattern for a Qualcomm LPG LED.
34 34
35 The pattern is a series of brightness and hold 35 The pattern is a series of brightness and hold-time pairs, with the hold-time
36 expressed in milliseconds. The hold time is a 36 expressed in milliseconds. The hold time is a property of the pattern and must
37 therefore be identical for each element in the !! 37 therefor be identical for each element in the pattern (except for the pauses
38 described below). As the LPG hardware is not a 38 described below). As the LPG hardware is not able to perform the linear
39 transitions expected by the leds-trigger-patte 39 transitions expected by the leds-trigger-pattern format, each entry in the
40 pattern must be followed a zero-length entry o 40 pattern must be followed a zero-length entry of the same brightness.
41 41
42 Simple pattern:: 42 Simple pattern::
43 43
44 "255 500 255 0 0 500 0 0" 44 "255 500 255 0 0 500 0 0"
45 45
46 ^ 46 ^
47 | 47 |
48 255 +----+ +----+ 48 255 +----+ +----+
49 | | | | ... 49 | | | | ...
50 0 | +----+ +---- 50 0 | +----+ +----
51 +----------------------> 51 +---------------------->
52 0 5 10 15 time (100ms) 52 0 5 10 15 time (100ms)
53 53
54 The LPG supports specifying a longer hold-time 54 The LPG supports specifying a longer hold-time for the first and last element
55 in the pattern, the so called "low pause" and 55 in the pattern, the so called "low pause" and "high pause".
56 56
57 Low-pause pattern:: 57 Low-pause pattern::
58 58
59 "255 1000 255 0 0 500 0 0 255 500 255 0 0 59 "255 1000 255 0 0 500 0 0 255 500 255 0 0 500 0 0"
60 60
61 ^ 61 ^
62 | 62 |
63 255 +--------+ +----+ +----+ +--- 63 255 +--------+ +----+ +----+ +--------+
64 | | | | | | | 64 | | | | | | | | ...
65 0 | +----+ +----+ +----+ 65 0 | +----+ +----+ +----+ +----
66 +-----------------------------> 66 +----------------------------->
67 0 5 10 15 20 25 time (100m 67 0 5 10 15 20 25 time (100ms)
68 68
69 Similarly, the last entry can be stretched by !! 69 Similarily, the last entry can be stretched by using a higher hold-time on the
70 last entry. 70 last entry.
71 71
72 In order to save space in the shared lookup ta 72 In order to save space in the shared lookup table the LPG supports "ping-pong"
73 mode, in which case each run through the patte 73 mode, in which case each run through the pattern is performed by first running
74 the pattern forward, then backwards. This mode 74 the pattern forward, then backwards. This mode is automatically used by the
75 driver when the given pattern is a palindrome. 75 driver when the given pattern is a palindrome. In this case the "high pause"
76 denotes the wait time before the pattern is ru 76 denotes the wait time before the pattern is run in reverse and as such the
77 specified hold-time of the middle item in the 77 specified hold-time of the middle item in the pattern is allowed to have a
78 different hold-time. 78 different hold-time.
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