LM3556 LED Driver

LM3556 flash와 torch mode

Texas Instruments LM3556은 high-side current source를 갖춘 1.5A synchronous boost LED flash driver입니다. Flash, torch, indicator 세 기능을 제공합니다.

Flash mode는 `CURRENT CONTROL REGISTER(0x09)`에서 93.75mA부터 1500mA까지 16단계 target current를 설정합니다. `ENABLE REGISTER(0x0A)` 또는 STROBE pin HIGH로 활성화합니다.

Userspace는 `/sys/class/leds/flash/brightness`로 flash를 제어합니다. 값 0은 off, 1은 93.75mA, 16은 1500mA입니다. STROBE pin mode가 켜져 있으면 sysfs 값은 brightness만 바꾸고 on/off는 STROBE pin이 제어합니다.

Torch mode도 register `0x09`에서 current를 program하고 register `0x0A` 또는 hardware TORCH input으로 활성화합니다. `/sys/class/leds/torch/brightness`에서 0은 off, 1은 46.88mA, 8은 375mA입니다.

========================
Kernel driver for lm3556
========================

* Texas Instrument:
  1.5 A Synchronous Boost LED Flash Driver w/ High-Side Current Source
* Datasheet: http://www.national.com/ds/LM/LM3556.pdf

Authors:
      - Daniel Jeong

        Contact:Daniel Jeong(daniel.jeong-at-ti.com, gshark.jeong-at-gmail.com)

Description
-----------
There are 3 functions in LM3556, Flash, Torch and Indicator.

Flash Mode
^^^^^^^^^^

In Flash Mode, the LED current source(LED) provides 16 target current levels
from 93.75 mA to 1500 mA.The Flash currents are adjusted via the CURRENT
CONTROL REGISTER(0x09).Flash mode is activated by the ENABLE REGISTER(0x0A),
or by pulling the STROBE pin HIGH.

LM3556 Flash can be controlled through /sys/class/leds/flash/brightness file

* if STROBE pin is enabled, below example control brightness only, and
  ON / OFF will be controlled by STROBE pin.

Flash Example:

OFF::

        #echo 0 > /sys/class/leds/flash/brightness

93.75 mA::

        #echo 1 > /sys/class/leds/flash/brightness

...

1500  mA::

        #echo 16 > /sys/class/leds/flash/brightness

Torch Mode
^^^^^^^^^^

In Torch Mode, the current source(LED) is programmed via the CURRENT CONTROL
REGISTER(0x09).Torch Mode is activated by the ENABLE REGISTER(0x0A) or by the
hardware TORCH input.

LM3556 torch can be controlled through /sys/class/leds/torch/brightness file.
* if TORCH pin is enabled, below example control brightness only,
and ON / OFF will be controlled by TORCH pin.

Torch Example:

OFF::

        #echo 0 > /sys/class/leds/torch/brightness

46.88 mA::

Indicator pattern과 brightness

Indicator pattern은 `/sys/class/leds/indicator/pattern`에서 선택합니다. `indicator_pattern` array에 pattern 0부터 3까지 네 개가 미리 정의되어 있습니다.

N-Blank, pulse time, N period 값의 조합으로 pattern을 생성합니다. Device-specific pattern이 필요하면 `indicator_pattern` array와 `INDIC_PATTERN_SIZE`를 수정하며 세 parameter의 의미는 datasheet를 참조합니다.

Pattern file에 0 또는 3 같은 index를 써서 선택합니다. Indicator brightness는 `/sys/class/leds/indicator/brightness`에서 제어하며 0은 off, 1은 5.86mA, 8은 46.875mA입니다.

        #echo 1 > /sys/class/leds/torch/brightness

...

375 mA::

        #echo 8 > /sys/class/leds/torch/brightness

Indicator Mode
^^^^^^^^^^^^^^

Indicator pattern can be set through /sys/class/leds/indicator/pattern file,
and 4 patterns are pre-defined in indicator_pattern array.

According to N-lank, Pulse time and N Period values, different pattern wiill
be generated.If you want new patterns for your own device, change
indicator_pattern array with your own values and INDIC_PATTERN_SIZE.

Please refer datasheet for more detail about N-Blank, Pulse time and N Period.

Indicator pattern example:

pattern 0::

        #echo 0 > /sys/class/leds/indicator/pattern

...

pattern 3::

        #echo 3 > /sys/class/leds/indicator/pattern

Indicator brightness can be controlled through
sys/class/leds/indicator/brightness file.

Example:

OFF::

        #echo 0 > /sys/class/leds/indicator/brightness

5.86 mA::

I2C board 등록

Driver는 `i2c_board_info` mechanism으로 등록된다고 가정합니다. 특정 adapter에서 address `0x63`의 chip을 등록하려면 `include/linux/platform_data/leds-lm3556.h`에 맞춰 platform data를 구성하고 I2C board info를 선언합니다.

예제는 `I2C_BOARD_INFO(LM3556_NAME, 0x63)`와 `.platform_data = &lm3556_pdata`를 사용합니다. Platform init function에서 `board_register_i2c_bus(4, 400, board_i2c_ch4, ARRAY_SIZE(board_i2c_ch4))`로 bus 4에 등록합니다.

        #echo 1 > /sys/class/leds/indicator/brightness

...

46.875mA::

        #echo 8 > /sys/class/leds/indicator/brightness

Notes
-----
Driver expects it is registered using the i2c_board_info mechanism.
To register the chip at address 0x63 on specific adapter, set the platform data
according to include/linux/platform_data/leds-lm3556.h, set the i2c board info

Example::

        static struct i2c_board_info board_i2c_ch4[] __initdata = {
                {
                         I2C_BOARD_INFO(LM3556_NAME, 0x63),
                         .platform_data = &lm3556_pdata,
                 },
        };

and register it in the platform init function

Example::

        board_register_i2c_bus(4, 400,
                                board_i2c_ch4, ARRAY_SIZE(board_i2c_ch4));