Pi 4 and official touchscreen not working

[jacklu333333]

I am using raspberry pi 4 and the official touchscreen. I config Pi 4 with an external HDMI display.
However, whenever the system boot into Linux, the display only shows the rainbow color, then the boot information of raspberry pi, and then it boot into the black screen.

I have digged into some topic related to this problem, but most of them says that the firmware of the touchscreen is already in the Archlinux kernel, it should work properly. To prove it was not due to out of box problem, I then install gnome to see whether the icon is display or not. However, the remains black with only back light. I could not and do not know how to find the log info to see where went wrong.

Hope someone can help me identify the problem.

Thanks in advance.

[jacklu333333]

I tried to reinstall from scratch, boot up, and configure with a touchscreen since the beginning. At first, the CLI UI show up successfully.
Once I install GUI interface, the touchscreen failed to display anything but the raspberry boot-up information.

I have tried sddm, lightdm, gdm with gnome and Xfce respectively. The same problem keeps showing up.

The uninstallation won't make the CLI touchscreen work again.

Also, the problem happened right after the installation instead of the system service start. So, I assume the problem has something to do with dm installation.

[graysky]

I haven't used the touchscreen. Perhaps there is some special setup you need to prevent output to HDMI0 or HDMI1? The fact that it boots correctly displaying to the touch screen but then stops when the greeter loads suggests there is either some special config you need to do. Which kernel are you running? (post uname -a) Any relevant output in your greeter's log or in journald? If not switch the greeter to a more verbose log setting.