Cannot run against VC4 GL driver (dtoverlay=vc4-kms-v3d)

[krzysztofkuczek]

Hi,
it works really fine! Thank you.
One question, is it possible to run it when experimental hardware OpenGL driver is enabled by adding line below to config.txt
dtoverlay=vc4-kms-v3d

In this case i get
vc_dispmanx_display_open failed!

Thank you !
Kris

[juj]

Glad the driver works out for you!

Unfortunately I am not familiar with the vc4-kms-v3d driver. Googling around, it looks like popcornmix commented in raspberrypi/firmware#556 (comment) that vc4-kms-v3d does not support dispmanx. Fbcp-ili9341 is based on top of dispmanx, which it uses to snapshot/acquire the rendered frame stream from the GPU.

Perhaps it may be possible to develop a corresponding rendered frame stream capture mechanism on top of the vc4-kms-v3d driver to use as a replacement for dispmanx in such scenarios.

I'll leave this entry open to highlight the unsupported configuration, in case someone knowledgeable might be able to pick this up.

[Kneesnap]

I would like to advocate for full KMS support too. I'm going to try my hand at it, but I make no guarantees. I have no idea what I'm doing.

[juj]

Testing on Raspberry Pi 4 with Raspbian Buster, with /boot/config.txt

dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
hdmi_group=2
hdmi_mode=87
hdmi_cvt=480 320 60 1 0 0 0
hdmi_force_hotplug=1

and

pi@raspberrypi:~ $ uname -a
Linux raspberrypi 4.19.66-v7l+ #1253 SMP Thu Aug 15 12:02:08 BST 2019 armv7l GNU/Linux

I notice that works with fbcp-ili9341 well. I am not familiar with the different display drivers, in particular about what the difference is betweenvc4-fkms-v3d vs vc4-kms-v3d, however I wonder if this observation about vc4-fkms-v3d would help anything for users here?

It is notable that hdmi_force_hotplug=1 is required for fbcp-ili9341 to work, updated the repo to add a note about that.