From 24e2d05d1b68981f22c984c766fabc5a93c83dba Mon Sep 17 00:00:00 2001 From: Bjorn Andersson Date: Thu, 3 Mar 2022 13:43:00 -0800 Subject: leds: Add driver for Qualcomm LPG The Light Pulse Generator (LPG) is a PWM-block found in a wide range of PMICs from Qualcomm. These PMICs typically comes with 1-8 LPG instances, with their output being routed to various other components, such as current sinks or GPIOs. Each LPG instance can operate on fixed parameters or based on a shared lookup-table, altering the duty cycle over time. This provides the means for hardware assisted transitions of LED brightness. A typical use case for the fixed parameter mode is to drive a PWM backlight control signal, the driver therefor allows each LPG instance to be exposed to the kernel either through the LED framework or the PWM framework. A typical use case for the LED configuration is to drive RGB LEDs in smartphones etc, for which the driver supports multiple channels to be ganged up to a MULTICOLOR LED. In this configuration the pattern generators will be synchronized, to allow for multi-color patterns. The idea of modelling this as a LED driver ontop of a PWM driver was considered, but setting the properties related to patterns does not fit in the PWM API. Similarly the idea of just duplicating the lower bits in a PWM and LED driver separately was considered, but this would not allow the PWM channels and LEDs to be configured on a per-board basis. The driver implements the more complex LED interface, and provides a PWM interface on the side of that, in the same driver. Signed-off-by: Bjorn Andersson Tested-by: Douglas Anderson Tested-by: Luca Weiss Reviewed-by: Marijn Suijten Tested-by: Marijn Suijten [On the Sony Xperia Nile Discovery, SDM630] Signed-off-by: Pavel Machek --- Documentation/leds/leds-qcom-lpg.rst | 76 ++++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 Documentation/leds/leds-qcom-lpg.rst (limited to 'Documentation/leds') diff --git a/Documentation/leds/leds-qcom-lpg.rst b/Documentation/leds/leds-qcom-lpg.rst new file mode 100644 index 000000000000..f12416f02dd8 --- /dev/null +++ b/Documentation/leds/leds-qcom-lpg.rst @@ -0,0 +1,76 @@ +.. 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). + +Simple pattern:: + + "255 500 0 500" + + ^ + | + 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 0 500 255 500 0 500" + + ^ + | + 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