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docs: leds: Add MT6370 RGB LED pattern document

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Document the MT6370 RGB LED pattern trigger.

This simply describe how the pattern works, each timing period, and the
pattern diagram for MT6370 RGB LED.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/38f1e863b0f099158a63fb6f95056a1cb30d80a0.1678430444.git.chiaen_wu@richtek.com
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ChiYuan Huang 2023-03-10 14:55:57 +08:00 committed by Lee Jones
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.. SPDX-License-Identifier: GPL-2.0
=========================================
The device for Mediatek MT6370 RGB LED
=========================================
Description
-----------
The MT6370 integrates a four-channel RGB LED driver, designed to provide a
variety of lighting effect for mobile device applications. The RGB LED devices
includes a smart LED string controller and it can drive 3 channels of LEDs with
a sink current up to 24mA and a CHG_VIN power good indicator LED with sink
current up to 6mA. It provides three operation modes for RGB LEDs:
PWM Dimming mode, breath pattern mode, and constant current mode. The device
can increase or decrease the brightness of the RGB LED via an I2C interface.
The breath 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 breath pattern for a MT6370 RGB LED.
The breath pattern is a series of timing pairs, with the hold-time expressed in
milliseconds. And the brightness is controlled by
'/sys/class/leds/<led>/brightness'. The pattern doesn't include the brightness
setting. Hardware pattern only controls the timing for each pattern stage
depending on the current brightness setting.
Pattern diagram::
"0 Tr1 0 Tr2 0 Tf1 0 Tf2 0 Ton 0 Toff" --> '0' for dummy brightness code
^
| ============
| / \ /
Icurr | / \ /
| / \ /
| / \ / .....repeat
| / \ /
| --- --- ---
|--- --- ---
+----------------------------------============------------> Time
< Tr1><Tr2>< Ton ><Tf1><Tf2 >< Toff >< Tr1><Tr2>
Timing description::
Tr1: First rising time for duty 0 to 30%.
Tr2: Second rising time for duty 31% to 100%.
Ton: On time for duty 100%.
Tf1: First falling time for duty 100% to 31%.
Tf2: Second falling time for duty 30% to 0%.
Toff: Off time for duty 0%.
Tr1/Tr2/Tf1/Tf2/Ton: 125ms to 3125ms, 200ms per step.
Toff: 250ms to 6250ms, 400ms per step.
Pattern example::
"0 125 0 125 0 125 0 125 0 625 0 1050"
This Will configure Tr1/Tr2/Tf1/Tf2 to 125m, Ton to 625ms, and Toff to 1050ms.