LCD

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1 S5P4418/S5P6818 1wire backlight adjustment

1.1 LCD backlight adjustment=

sudo sh -c "echo '10' >/dev/backlight-1wire"

value range：0~127

1.2 Turn off the LCD backlight

sudo sh -c "echo '0' >/dev/backlight-1wire"

2 RK3399 platform: adjust the LCD backlight

The backlight can be controlled manually through the node in this path: /sys/class/backlight/backlight

3 S5P6818 platform: Add your own screen support

3.1 Kernel 4.4

3.1.1 Display driver

It is recommended to debug uboot v2016.01, the relevant files are located in board/s5p6818/nanopi3/ , focusing on lcds.c
Debugging the kernel 4.4 again, the driver is drivers/gpu/drm/panel/panel-friendlyelec.c

3.1.2 Touch Screen Driver

You may refre to HD900 touch screen driver:

   drivers/input/touchscreen/friendlyelec/st1572.c

Or the following driver:

   drivers/input/touchscreen/st1232.c

3.2 Kernel 3.4

For Android, to add your own screen support, you need to modify u-boot-2014.07 and linux-3.4.y. you can download and compile these 2 parts according to the wiki.

u-boot-2014.07
board/s5p6818/nanopi3/lcds.c - 包含了我们所支持的屏的时序信息
board/s5p6818/nanopi3/onewire.c - 这是一线的实现，主要是用来识别屏
board/s5p6818/nanopi3/board.c - bd_lcd_init() 是屏的初始化处理
对于用户自己的屏，可以先修改 lcds.c ，增加自己的屏的参数，然后强制使用自己的参数
另外，部分屏因硬件特性的差异，初始化时需要配置不同的IO驱动能力，这需要根据自己实际的情况来测试，具体可查看命令类似 _gpio_init 的函数
如果用户的屏的LVDS 接口的，则nanopi2_lcd_config 中是通过 LCD_VESA

uboot中屏显示正常后，便可移植linux-3.4.y

linux-3.4.y
arch/arm/plat-s5p6818/nanopi3/lcds.c - 和 uboot中的类似，包含了屏的时序参数
可将uboot已调试好的参数增加到这里，这时候需要留意一下内核命令参数 lcd=XXX ，uboot会传递此参数给内核。

4 T4，M4安卓7修改屏幕方向的问题

第一步: 使用Type-C连接PC与板子，在PC上使用adb 拉取板子上的文件到PC上
adb pull /system/build.prop
第二步: 在PC上修改 build.prop
a) 修改 ro.sf.hwrotation=90
b) 增加 sys.hwc.device.primary=HDMI-A
第三步: 在PC上使用以下命令将修改过的 build.prop 推送到板子
adb root; adb remount; adb push build.prop /system/
第四步: 重启板子，可使用以下命令重启板子
adb reboot

5 T4 H702E LCD driver

drivers/gpu/drm/panel/panel-friendlyelec.c
drivers/gpu/drm/panel/panel-friendlyelec.h

And DTS file:
arch/arm64/boot/dts/rockchip/rk3399-nanopi4-common.dtsi

Related configuration:

    panel: edp-panel {
        compatible = "lcds", "simple-panel";
        status = "okay";

        backlight = <&pwm_bl>;
        power-supply = <&vcc_lcd>;
        prepare-delay-ms = <20>;
        enable-delay-ms = <20>;

        ports {
            edp_panel: endpoint {
                remote-endpoint = <&edp_out>;
            };
        };
    };

6 HD702 touch screen driver

touch screen: gt9xx
linux 3.4: drivers/input/touchscreen/gt9xx.c
linux 4.4: drivers/input/touchscreen/friendlyelec/gt9xx.c