FKMS: transparency artifact in drm formats AR24 and AB24

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
linux
Domain
operating-systems

Research direction

Reproduce the artifact in FKMS using the documented modetest commands with AR24 and AB24, after enabling vc4-fkms-v3d. Start by comparing the FKMS result with non-firmware KMS and review the reported logs; the work is done when those formats display without the translucent top-left image artifact.

Written by the indexing model from the issue text.

Description

Describe the bug
While run modetest -P 75@85:800x480@AR24 in fkms mode on yocto I see artifact in top-left quarter of screen. (My screen is upside down).
The issue observed on AR24 and AB24 formats. May be another with alpha channel.
No dependency on plane resolution.
I don't observe the same issue in non-firmware KMS mode.

To reproduce
tested on yocto core-image-sato in fkms mode (set dtoverlay=vc4-fkms-v3d in /boot/config.txt).

kill 'GUI window manager'
modetest -p # retrieve CRTC id and plane id
modetest -P <plane_id>@<crtc_id>:800x480@AR24
modetest -P <plane_id>@<crtc_id>:800x480@AB24

also
modetest -s 89:#0@AR24 -P 38@87:600x280@AR24

Expected behaviour
No artifacts should be seen

Actual behaviour
There is a part of image in top-left quarter of screen, which have about 50% of transparency.
modetest -P 75@85:800x480@AR24
image
modetest -s 89:#0@AR24 -P 38@87:600x280@AR24 -C
image

System

  • Which model of Raspberry Pi? e.g. Pi3B+, PiZeroW
    Pi 4B 8Gb + DSI LCD 7"
  • Which OS and version (cat /etc/rpi-issue)?
    Yocto core-image-sato
  • Which firmware version (vcgencmd version)?
    The latest from https://github.com/raspberrypi/firmware/tree/master/boot at the moment
  • Which kernel version (uname -a)?

Linux raspberrypi4-64 5.15.34-v8 #1 SMP PREEMPT Tue Apr 19 19:21:26 UTC 2022 aarch64 GNU/Linux

Logs
modetest -P 38@87:800x480@AR24
testing 800x480@AR24 overlay plane 38

modetest_p_fkms.log
modetest_c_fkms.log
modetest_e_fkms.log

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