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- .. SPDX-License-Identifier: GPL-2.0
- ==============================
- Kernel driver for Qualcomm LPG
- ==============================
- Description
- -----------
- The Qualcomm LPG can be found in a variety of Qualcomm PMICs and consists of a
- number of PWM channels, a programmable pattern lookup table and a RGB LED
- current sink.
- To facilitate the various use cases, the LPG channels can be exposed as
- individual LEDs, grouped together as RGB LEDs or otherwise be accessed as PWM
- channels. The output of each PWM channel is routed to other hardware
- blocks, such as the RGB current sink, GPIO pins etc.
- The each PWM channel can operate with a period between 27us and 384 seconds and
- has a 9 bit resolution of the duty cycle.
- In order to provide support for status notifications with the CPU subsystem in
- deeper idle states the LPG provides pattern support. This consists of a shared
- lookup table of brightness values and per channel properties to select the
- range within the table to use, the rate and if the pattern should repeat.
- The pattern for a channel can be programmed using the "pattern" trigger, using
- the hw_pattern attribute.
- /sys/class/leds/<led>/hw_pattern
- --------------------------------
- Specify a hardware pattern for a Qualcomm LPG LED.
- The pattern is a series of brightness and hold-time pairs, with the hold-time
- expressed in milliseconds. The hold time is a property of the pattern and must
- therefor be identical for each element in the pattern (except for the pauses
- described below). As the LPG hardware is not able to perform the linear
- transitions expected by the leds-trigger-pattern format, each entry in the
- pattern must be followed a zero-length entry of the same brightness.
- Simple pattern::
- "255 500 255 0 0 500 0 0"
- ^
- |
- 255 +----+ +----+
- | | | | ...
- 0 | +----+ +----
- +---------------------->
- 0 5 10 15 time (100ms)
- The LPG supports specifying a longer hold-time for the first and last element
- in the pattern, the so called "low pause" and "high pause".
- Low-pause pattern::
- "255 1000 255 0 0 500 0 0 255 500 255 0 0 500 0 0"
- ^
- |
- 255 +--------+ +----+ +----+ +--------+
- | | | | | | | | ...
- 0 | +----+ +----+ +----+ +----
- +----------------------------->
- 0 5 10 15 20 25 time (100ms)
- Similarily, the last entry can be stretched by using a higher hold-time on the
- last entry.
- In order to save space in the shared lookup table the LPG supports "ping-pong"
- mode, in which case each run through the pattern is performed by first running
- the pattern forward, then backwards. This mode is automatically used by the
- driver when the given pattern is a palindrome. In this case the "high pause"
- denotes the wait time before the pattern is run in reverse and as such the
- specified hold-time of the middle item in the pattern is allowed to have a
- different hold-time.
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