From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- Documentation/leds/leds-qcom-lpg.rst | 78 ++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 Documentation/leds/leds-qcom-lpg.rst (limited to 'Documentation/leds/leds-qcom-lpg.rst') diff --git a/Documentation/leds/leds-qcom-lpg.rst b/Documentation/leds/leds-qcom-lpg.rst new file mode 100644 index 000000000..de7ceead9 --- /dev/null +++ b/Documentation/leds/leds-qcom-lpg.rst @@ -0,0 +1,78 @@ +.. 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//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. -- cgit v1.2.3