[Buildroot] EGLFS Could Not Find DRM Device!

Charles Steinkuehler charles at steinkuehler.net
Sun Aug 29 15:28:34 UTC 2021


On 8/28/2021 10:03 PM, Charles Steinkuehler wrote:
> 
> Sorry to jump in, I'm new to Buildroot and this list but I am having the 
> same issue: Using a RPi4 with the latest buildroot (master pulled from 
> git) and no /dev/dri/ devices show up even though config.txt contains:
> 
>     dtoverlay=vc4-kms-v3d-pi4
> 
> ...and the overlay files are present on the first (vfat) partition.
> 
> I started with the raspberrypi4_64_defconfig, switched to glibc, and 
> added a few packages (mesa, kmscube, SDL2).
> 
> On a whim I switched init from the busybox default to systemd (which 
> also pulled in udev), and *PRESTO* I now have a /dev/dri/ folder with 
> devices (after once again adding the config.txt dtoverly line for the 
> kms driver)!
> 
> Is there any documentation about the minimum environment needed to get 
> the vc4-kms drivers running?  Do I need full systemd/udev, is mdev 
> enough, or should devtmpfs be working but perhaps I'm missing something 
> else in the rootfs image?  Is init maybe the problem vs. /dev handling?

Update on what does/doesn't work:

Busybox init + devtmpfs = FAIL
Busybox init + devtmpfs + mdev = FAIL
Busybox init + devtmpfs + eudev = WORKS
systemd + udev = WORKS

I don't know enough about mdev to know if it should be possible to get 
it working vs. eudev.  I may look into that in the future but right now 
I'm just happy to have a system working that doesn't need to pull in all 
of systemd.

For clarity, "WORKS" above means I simply add the 
"dtoverlay=vc4-kms-v3d-pi4" to config.txt, boot, and running "kmscube" 
at the command prompt yields the expected spinning cube.  I also have a 
properly populated /dev/dri, and kmscube reports it is using Broadcom 
V3D 4.2 for OpenGL ES rendering.

-- 
Charles Steinkuehler
charles at steinkuehler.net


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