2147474_en-US

[#1]

Why do I get "Permission denied" when enabling different overlay planes with modetest on i.MX8 DRM?

Hello,

I am working on an i.MX platform and testing overlay planes using the modetest tool. I noticed that when I try to enable certain overlay planes, I get a "Permission denied" error, while others work fine.

Here are the commands and results:

• For plane 70:

modetest -P 70@69:1024x768
# ... testing 1024x768@XR24 overlay plane 70
# (Success)

• For plane 84:

modetest -P 84@69:1024x768
# ... testing 1024x768@XR24 overlay plane 84
# failed to enable plane: Permission denied

Why does enabling some planes work but others return "Permission denied"?
Is there any hardware or driver limitation that restricts the use of certain planes?
Or could this be related to permissions, resource conflicts, or something else?

Any advice or documentation reference would be appreciated!

Thank you.

Re: Why do I get "Permission denied" when enabling different overlay planes with modetest

hi @longzimggg 

PLease type the modetest -l command show the result. 

and You cannot independently and simultaneously operate multiple planes on the same CRTC directly. This limitation mainly comes from the DRM framework and driver resource management, not from the hardware itself.

B.R

Re: Why do I get "Permission denied" when enabling different overlay planes with modetest

Let me clarify my situation:
Currently, I am using the same CRTC. I believe the issue is related to using the same CRTC. However, what I want to achieve is to render with different planes of the same CRTC from different processes.