[Buildroot] EGLFS Could Not Find DRM Device!

From: Charles Steinkuehler <charles@steinkuehler.net>
To: buildroot@busybox.net
Subject: [Buildroot] EGLFS Could Not Find DRM Device!
Date: Sat, 28 Aug 2021 22:03:40 -0500	[thread overview]
Message-ID: <f3bef982-d139-cd08-2477-33383a5d67ca@steinkuehler.net> (raw)

> Hello Scott,
> 
> On Wed, 18 Aug 2021 20:28:12 +0000, Scott Bartolett <SBartolett at thorlabs.com> wrote:
> 
>> Yes I have the BR2_PACKAGE_RPI_FIRMWARE_INSTALL_DTB_OVERLAYS enabled and rpi-firmware/overlays entry in genimage.  If I search the buildroot output folder I find this:
>>
>> ./output/images/rpi-firmware/overlays/vc4-kms-v3d.dtbo
>> ./output/images/rpi-firmware/overlays/vc4-kms-v3d-pi4.dtbo
>> ./output/build/rpi-firmware-1a46874494146f470d7a61b0b6f4f15a07dd8b35/boot/overlays/vc4-kms-v3d.dtbo
>> ./output/build/rpi-firmware-1a46874494146f470d7a61b0b6f4f15a07dd8b35/boot/overlays/vc4-kms-v3d-pi4.dtbo
>>
>> But I do not find those files anywhere on the target machine.  I am using a root file system overlay.  Might that be my problem?
> 
> The overlays are stored in the first/boot partition (vfat one where the dtb files,
> config.txt and cmdline.txt, bootcode.bin and start.elf and fixup.dat and zimage
> are found) and not on the second/root (ext4 one with the complte root file system)
> partition of the SD card...

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?

-- 
Charles Steinkuehler
charles@steinkuehler.net
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