No composite output with full KMS

[Setiawan]

I posted this on the Raspberry Pi forums initially, but figured I'd try my luck here too. The main reason I'm trying to switch to full KMS is because I hear that it can help with the screen tearing issue, after all.

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I'm running an 8GB Pi 4 Model B. Kernel has been updated to 5.10.9-v7l+. Pi is connected only to composite output.

config.txt:

disable_overscan=1
hdmi_ignore_hotplug=1
dtparam=audio=on

[pi4]
dtoverlay= vc4-kms-v3d
max_framebuffers=2

[all]
enable_tvout=1
sdtv_aspect=1
sdtv_mode=16
gpu_mem=256

With this config, when I turn on the Pi 4, I get the rainbow splash screen momentarily, and after that, it's just blank. If I use vc4-fkms-v3d instead though (like I had previously been doing), I get normal screen output through composite.

I notice that when I run modetest -M vc4 (while using vc4-fkms-v3d), it shows one connector: "composite-1", with a status of "connected"

However, when I run modetest -M vc4 (while using vc4-kms-v3d), it shows two connectors: HDMI-A-1 and HDMI-A-2, both of which have a status of disconnected.

It seems like using full KMS makes the pi ignore some of the config.txt (such as enable_tvout).

Does anyone know why this may be happening, and how I would go about fixing this so I can use full KMS and composite output?

[busywait]

@setiawan

Is this relevant? [pi4] Experimental KMS driver causing freeze on boot when using composite?

Also is this note in the 5.10 kernel thread relevant?
"vc4-kms-v3d is totally independent of the firmware for rendering, so any of the dpi_[group|mode|timings] and enable_dpi_lcd options in config.txt are irrelevant."

[Setiawan]

@busywait Thanks for that, I added "composite=1" to the "dtoverlay" line in config.txt, and it has had some change, but the screen is still blank.

Now when I run modetest, the connector "composite-1" shows up, but its status is "unknown", and it has no associated encoder id.

The list of encoders has also changed to include TVDAC, but it has a crtc of 0.

TBH I'm not sure how connector, encoder, and crtc interrelate, and/or whether it's possible to fix the relations (assuming that's all the problem is).