Commit 24e2d05d authored by Bjorn Andersson's avatar Bjorn Andersson Committed by Pavel Machek
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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: default avatarBjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: default avatarDouglas Anderson <dianders@chromium.org>
Tested-by: default avatarLuca Weiss <luca@z3ntu.xyz>
Reviewed-by: default avatarMarijn Suijten <marijn.suijten@somainline.org>
Tested-by: default avatarMarijn Suijten <marijn.suijten@somainline.org>
[On the Sony Xperia Nile Discovery, SDM630]
Signed-off-by: default avatarPavel Machek <pavel@ucw.cz>
parent a8e53db4

Documentation/leds/leds-qcom-lpg.rst

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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).



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.

drivers/leds/Kconfig

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@@ -869,6 +869,9 @@ source "drivers/leds/blink/Kconfig" 
comment "Flash and Torch LED drivers"

source "drivers/leds/flash/Kconfig"



comment "RGB LED drivers"

source "drivers/leds/rgb/Kconfig"



comment "LED Triggers"

source "drivers/leds/trigger/Kconfig"

drivers/leds/Makefile

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@@ -99,6 +99,9 @@ obj-$(CONFIG_LEDS_USER) += uleds.o 
# Flash and Torch LED Drivers

obj-$(CONFIG_LEDS_CLASS_FLASH)		+= flash/



# RGB LED Drivers

obj-$(CONFIG_LEDS_CLASS_MULTICOLOR)	+= rgb/



# LED Triggers

obj-$(CONFIG_LEDS_TRIGGERS)		+= trigger/

drivers/leds/rgb/Kconfig

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# SPDX-License-Identifier: GPL-2.0



if LEDS_CLASS_MULTICOLOR



config LEDS_QCOM_LPG

	tristate "LED support for Qualcomm LPG"

	depends on OF

	depends on SPMI

	help

	  This option enables support for the Light Pulse Generator found in a

	  wide variety of Qualcomm PMICs. The LPG consists of a number of PWM

	  channels and typically a shared pattern lookup table and a current

	  sink, intended to drive RGB LEDs. Each channel can either be used as

	  a LED, grouped to represent a RGB LED or exposed as PWM channels.



	  If compiled as a module, the module will be named leds-qcom-lpg.



endif # LEDS_CLASS_MULTICOLOR

drivers/leds/rgb/Makefile

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# SPDX-License-Identifier: GPL-2.0



obj-$(CONFIG_LEDS_QCOM_LPG)	+= leds-qcom-lpg.o