79 lines
2.9 KiB
ReStructuredText
79 lines
2.9 KiB
ReStructuredText
|
.. 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
|
||
|
|
therefore 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)
|
||
|
|
|
||
|
|
Similarly, 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.
|