I run most of my Raspberry Pi systems headless, so I was a bit surprised that OpenSuSE tumbleweed on a Raspberry Pi 3B didn’t show anything on my HDMI monitor after I installed KDE after it switches away from text-mode boot output.
[WayBack] HCL:Raspberry Pi3 – openSUSE suggests to
I see HDMI output in U-Boot, but not in Linux
The upstream Linux graphics driver for the Raspberry Pi has problems with a few monitors. The same applies to the 7″ LCD displays. In those cases, please fall back to the efi frame buffer console by passing the following into the kernel command line:
modprobe.blacklist=vc4
However, it does not explain how to modify that “the kernel command line”.
Searching for obvious ways via “Raspberry Tumbleweed Kernel Command Line” got me to for instance
which all suggest editing /boot/cmdline.txt, however that file does not exist:
# ls -al /boot
total 34624
drwxr-xr-x 6 root root 4096 Jul 23 21:05 .
drwxr-xr-x 24 root root 4096 Jul 16 02:02 ..
-rw-r--r-- 1 root root 65 Jul 16 12:42 .Image-4.4.76-7-default.hmac
-rw-r--r-- 1 root root 0 Jul 16 16:56 0x75b762d5
lrwxrwxrwx 1 root root 22 Jul 16 16:34 Image -> Image-4.4.76-7-default
-rw-r--r-- 1 root root 14878208 Jul 16 12:20 Image-4.4.76-7-default
-rw-r--r-- 1 root root 3217519 Jul 16 12:20 System.map-4.4.76-7-default
lrwxrwxrwx 1 root root 1 Jul 16 02:00 boot -> .
-rw-r--r-- 1 root root 1725 May 24 20:11 boot.readme
-rw-r--r-- 1 root root 2405 Jul 16 16:56 boot.scr
-rw-r--r-- 1 root root 2333 Jul 16 16:56 boot.script
-rw-r--r-- 1 root root 152522 Jul 16 08:39 config-4.4.76-7-default
lrwxrwxrwx 1 root root 12 Jul 23 16:13 dtb -> dtb-4.11.6-1
drwxr-xr-x 3 root root 4096 Jul 23 16:13 dtb-4.11.6-1
drwxr-xr-x 5 root root 16384 Jan 1 1970 efi
drwxr-xr-x 7 root root 4096 Jul 24 18:27 grub2
lrwxrwxrwx 1 root root 23 Jul 16 16:34 initrd -> initrd-4.4.76-7-default
-rw------- 1 root root 8080932 Jul 23 21:05 initrd-4.4.76-7-default
-rw-r--r-- 1 root root 288571 Jul 16 12:42 symvers-4.4.76-7-default.gz
-rw-r--r-- 1 root root 377 Jul 16 12:42 sysctl.conf-4.4.76-7-default
-rw-r--r-- 1 root root 1484762 Jul 16 16:56 unicode.pf2
drwxr-xr-x 2 root root 4096 Jul 24 09:05 vc
-rw-r--r-- 1 root root 7282031 Jul 15 07:00 vmlinux-4.4.76-7-default.gz
There are other config.txt files:
# find / | grep config.txt
/boot/efi/config.txt
/boot/vc/config.txt
However, these seems to be unclear which of the two is actually used and what options can be set at all: [WayBack] Raspberry Pi • View topic – aarch64 on Pi3.
So the quest continues, as a lot of settings can be applied in these files:
Setting “modprobe.blacklist=vc4”
I’ve temporarily given up on the /boot/config.txt editing, but continued searching for “modprobe.blacklist=vc4”, which lead to a few interesting results:
All of those suggest adding modprobe.blacklist=vc4 to the grub configuration. The second post actually has the most elaborate steps for this, which I’ve paraphrased into:
- As
root, edit /etc/default/grub (make a backup first)
- Search for the variable
GRUB_CMDLINE_LINUX
- Add the
modprobe.blacklist=vc4to the end of the variable initialisation (ensure there is a space before it and you keep the terminating double-quote)
- Re-generate the grub configuration file used at boot time (make a backup first):
grub2-mkconfig > /boot/grub2/grub.cfg
This solved my problem: no text output on HDMI.
Note that in order to get graphical output, you need to install any of the non-JeOS images. Installing just kde+kdm and dependencies isn’t enough to get the X server going.
–jeroen
Using 
The Wiert Corner - irregular stream of stuff 