summaryrefslogtreecommitdiffstats
path: root/Documentation/leds/leds-qcom-lpg.rst
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/leds/leds-qcom-lpg.rst
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/leds/leds-qcom-lpg.rst')
-rw-r--r--Documentation/leds/leds-qcom-lpg.rst78
1 files changed, 78 insertions, 0 deletions
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/<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.