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The cpu of Radxa Rock - RK3188 has two LCD controllers, LCD0 and LCD1. On RR, LCD1 is connected to HDMI and LCD0 is connect to AV out and the LCD0 signal are also exported on the extension header.

There is some sysfs interface exported to control the display related stuff. The following should work on both Android and Linux.

Set display scale

   root@radxa:# export SCALE=/sys/class/graphics/fb0/scale
   #For the new Ubuntu 14.04 image, the path is changed to /sys/class/display/HDMI/scale, run
   root@radxa:# export SCALE=/sys/class/display/HDMI/scale
   root@radxa:# cat $SCALE
   xscale=95 yscale=95
   root@radxa:# echo 100 > $SCALE
   root@radxa:# cat $SCALE
   xscale=100 yscale=100

You can also set different scales for X and Y:

   root@radxa:# echo xscale=80 > $SCALE
   root@radxa:# echo yscale=100 > $SCALE
   root@radxa:# cat $SCALE
   xscale=80 yscale=100

Set HDMI output mode

you can see supported output modes by the following commands:

   root@radxa:# cat /sys/class/display/display0.HDMI/modes
   #For the new Ubuntu 14.04 image, the path is changed to
   root@radxa:# cat /sys/class/display/HDMI/modes

check out the current display mode

   root@radxa:# cat /sys/class/display/display0.HDMI/mode
   #For the new Ubuntu 14.04 image, the path is changed to
   root@radxa:# cat /sys/class/display/HDMI/mode

It's 720p@60hz

change the mode to 1080p@60hz

   root@radxa:# echo 1920x1080p-60 > /sys/class/display/display0.HDMI/mode
   #For the new Ubuntu 14.04 image, the path is changed to
   root@radxa:# echo 1920x1080p-60 > /sys/class/display/HDMI/mode

Set font size of X and console

Change DPI to increase the font size in X

rock@radxa:~$ sudo nano ~/.Xresources

add the following lines:

! Xft settings 
Xft.dpi: 120
Xft.antialias: true
Xft.rgba: rgb
Xft.hinting: true
Xft.hintstyle: hintslight

Change the console settings:

rock@radxa:~$ sudo dpkg-reconfigure console-setup

Go through the setup: hit enter, hit enter, choose the font and hit enter, hit enter, choose size and hit enter

Switch to console via ctrl+alt+f1 and verify your settings:

root@radxa:~# setupcon

Find the best solution by repeating the console-setup...

Set full color depth

To use full 24/32 bits color depth on the radxa rock linux image:

apt-get install fbset
cat <<eof>> /etc/init/fbset.conf
# fbset - run fbset to set truecolor fbmode
description "run fbset ASAP"
start on startup and started udev or starting lightdm
    echo 0 > /sys/class/display/HDMI/enable
    [ -x /bin/fbset ] && /bin/fbset -a -nonstd 1 -depth 32 -rgba "8/0,8/8,8/16,8/24"
    echo 1 > /sys/class/display/HDMI/enable
end script
cat <<eof>> /etc/X11/xorg.conf
Section "Screen"
    Identifier "Default Screen"
    DefaultDepth 24

After rebooting you should not see green/purple screen. If you do, something went wrong. You can then use serial console or SSH from another machine and manually submit these commands:

service lightdm stop
fbset -a -nonstd 1 -depth 32 -rgba 8/0,8/8,8/16,8/24
service lightdm start

To make this change permanent, timing is critical during bootup. fbset will need to be called before X / lightdm starts. In Linaro/Ubuntu an upstart script is needed - fbset.conf - see above. The condition "startup and started udev" will try to run fbset as early as possible. On my rk3188 this works reliably, but if you have issues, your best bet is to tinker with these "start on" conditions. Do not use /etc/rc.local for this - this script is run long after lightdm has been started by upstart.

Set framebuffer resolution

Set framebuffer resolution to 720 x 480 pixels

service lightdm stop
fbset -a -xres 720  -yres  480 -vxres 720  -vyres  480
service lightdm start

If you get a blank screen, try to reactivate the display

echo 1 > /sys/class/graphics/fb0/enable

A few examples of other framebuffer resolution settings: 720x576, 1024x600, 1280x720, 1920x1080

fbset -a -xres 720  -yres  576 -vxres 720  -vyres  576
fbset -a -xres 1024 -yres  600 -vxres 1024 -vyres  600
fbset -a -xres 1280 -yres  720 -vxres 1280 -vyres  720
fbset -a -xres 1920 -yres 1080 -vxres 1920 -vyres 1080