GPIO觸發LED

前置條件:
1. LED是用keypad 的backlight LED
2. GPIO 為INPUT (似按button後導通)

 整體行為:
當GPIO為 PULL_HIGH時, LED亮
當GPIO為 PULL_DOWN時, LED滅

相關的driver code:
kernel/drivers/led/led-class.c, led-core.c, leds-qpnp.c, led-triggers.c, ledtrig-gpio.c
看完code可發現, 此功能若依kernel的code 只能用 device node的設定來變更GPIO的pin值,
無法用devicetree 來直接指定 (所以此文是修改啟動script來設定GPIO pin number)

1. 開啟 kernel 功能 (修改 default_config 檔: kernel/arch/arm/configs/msm8974_defconfig )

　加入: 

　CONFIG_LEDS_QPNP=y

　CONFIG_LEDS_TRIGGERS=y

　CONFIG_LEDS_TRIGGER_BACKLIGHT=y

　CONFIG_LEDS_TRIGGER_GPIO=y

　CONFIG_LEDS_TRIGGER_DEFAULT_ON=y

2. 設定GPIO行為 (修改 kernel/arch/arm/mach-msm/board-msm8974-gpiomux.c)

static struct gpiomux_setting button_act_cfg = {

        .func = GPIOMUX_FUNC_GPIO,

        .drv = GPIOMUX_DRV_2MA,

        .pull = GPIOMUX_PULL_NONE,

        .dir = GPIOMUX_IN,

};

static struct gpiomux_setting button_sus_cfg = {

        .func = GPIOMUX_FUNC_GPIO,

        .drv = GPIOMUX_DRV_2MA,

        .pull = GPIOMUX_PULL_DOWN,

};

static struct msm_gpiomux_config msm_BUTTON_config[] __initdata = {

        {

                .gpio = GPIO_BUTTON,  //79

                .settings = {

                        [GPIOMUX_ACTIVE]  = &button_act_cfg,

                        [GPIOMUX_SUSPENDED]  = &button_sus_cfg,

                },

        },

};

void __init msm_msmd8974_init_gpiomux(void)

{

...

msm_gpiomux_install(msm_BUTTON_config, ARRAY_SIZE(msm_BUTTON_config));

}

3. 設定 LED與指定用GPIO觸發 (kernel/arch/arm/boot/dts/msm8974-leds.dtsi)

&pm8941_lsid1 {

...

    qcom,leds@e200 {

    ...

    qcom,kpdbl4 {

                        label = "kpdbl";

                        linux,name = "kpdbl-pwm-4";

                        qcom,mode = "pwm";

                        qcom,pwm-channel = <11>;

                        qcom,pwm-us = <1000>;

                        qcom,id = <7>;

                        qcom,max-current = <20>;

                        qcom,row-id = <3>;

                        qcom,row-src-en;

                        qcom,always-on;

                        qcom,default-state = "off";

                        linux,default-trigger = "gpio";

      };

4. 指定GPIO 值與設定亮度等, 這部份自己找 啟動scripts 放, 我是放在 (device/qcom/common/rootdir/etc/init.qcom.sh)

        echo gpio > /sys/class/leds/kpdbl-pwm-4/trigger

        echo 255 > /sys/class/leds/kpdbl-pwm-4/desired_brightness

        echo 255 > /sys/class/leds/kpdbl-pwm-4/brightness

        echo 79 > /sys/class/leds/kpdbl-pwm-4/gpio