princec
Posts: 39
Joined: Fri Sep 02, 2011 11:01 am
Contact: Website

RPi3 / VC4 KMS driver / 7" display = blank

Mon May 17, 2021 10:43 pm

I've got a buildroot system here running on a Pi3 with the official 7" display attached.

When I use dtoverlay=vc4-fkms-v3d in config.txt, everything's good - logs show up, my OpenGLES app runs, but there's this terrible vsyncing problem causing it to flicker badly almost as if it's single-buffered.

So I hear the fix is to use the more recently maintained kms driver: dtoverlay=vc4-kms-v3d
However... no display ever comes up - it's black. It's running ok otherwise, just no output at all.

Perhaps there are some other parameters I need to set?

aBUGSworstnightmare
Posts: 3203
Joined: Tue Jun 30, 2015 1:35 pm

Re: RPi3 / VC4 KMS driver / 7" display = blank

Tue May 18, 2021 5:05 am

Have you added the required overlays to config.txt for using the 7in under KMS?

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 11481
Joined: Wed Dec 04, 2013 11:27 am
Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: RPi3 / VC4 KMS driver / 7" display = blank

Tue May 18, 2021 6:11 am

dtoverlay=vc4-kms-dsi-7inch
would be the line needed.
Linux doesn't have a nice way of autodetecting DSI displays as there are a million and one potentials that could be connected. The firmware knows about 1 display, so can try it out and see if it works.

I'm still fighting this driver to get it to be reliable though.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

cleverca22
Posts: 3953
Joined: Sat Aug 18, 2012 2:33 pm

Re: RPi3 / VC4 KMS driver / 7" display = blank

Tue May 18, 2021 7:04 am

would it be possible for the firmware to auto-detect that panel, and the fact that your using the real kms driver, then auto-load the dsi overlay too?

princec
Posts: 39
Joined: Fri Sep 02, 2011 11:01 am
Contact: Website

Re: RPi3 / VC4 KMS driver / 7" display = blank

Tue May 18, 2021 10:27 am

Tried

Code: Select all

dtoverlay=vc4-kms-dsi-7inch
but no joy - there's no /dev/dri directory created and so there's no card0 etc.

So I'm assuming that I also need

Code: Select all

dtoverlay=vc4-kms-v3d
... so I tried adding it. I got the display back then but unfortunately attempting to actually render something caused me a crash before I could get it to init (something to do with determining available modes).
I wonder though if I'm on the right track, and need to now also specify some video mode related parameters in config.txt too?

Yours cluelessly,
Cas :)

Return to “Official Foundation Display”