[SOLVED] Dual monitor on RPi4

louigi600 · 03-03-2021, 05:22 AM

Has anyone had any luck with using 2 displays connected to the RPi4 ?
With the default /boot/config.txt I can get one display to work in whatever port I use but if I try both at the same time the second display just shows the color boot splash.
On the RPiOS it seems to work fine.

If I put this in the config.txt I can get the text console to appear on both displays:

Code:

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

But if I start X I don't get the normal window manager appearance, instead just the application bar and the rest black (both monitors show the same thing).
xrandr seems to have an issue and is not showing the second display anyway so I don't know how to tell it to use the second display as an extension rather than duplicating them.

pan64 · 03-03-2021, 05:59 AM

I think you can find some ideas/info here: https://www.raspberrypi.org/forums/v...c.php?t=244558

louigi600 · 03-03-2021, 06:19 AM

@PAN64
I saw that ... but it seems to be an old thread ... on RPiOS it now works out of the box.
As I edited above: by uncommenting some stuff in the config.txt I can get both monitors to sow something ... but not much control over it.
On slackwarearm-current xrandr does not show the 2 displays so I'm not sure how to tell X what to do with them + there is something else wrong because I don't get the normal window manager appearance.

pan64 · 03-03-2021, 06:33 AM

there were some config.txt settings to try and probably you can try that tvservice command too (if available).
Probably this issue is slackware specific (and does not depend on the config), but first I would check this config file line by line.

louigi600 · 03-03-2021, 07:58 AM

With a little work I got the /opt/vc to work on slackwarearm-current:

Code:

root@rpi4:/opt/vc/bin# ./tvservice -l
2 attached device(s), display ID's are : 
Display Number 2, type HDMI 0
Display Number 7, type HDMI 1
root@rpi4:/opt/vc/bin# ./tvservice -n -v 2
device_name=SAM-S24F350
root@rpi4:/opt/vc/bin# ./tvservice -n -v 7
device_name=SAM-S24D330
root@rpi4:/opt/vc/bin# ./tvservice -m DMT -v 2
Group DMT has 18 modes:
           mode 4: 640x480 @ 60Hz 4:3, clock:25MHz progressive 
           mode 5: 640x480 @ 72Hz 4:3, clock:31MHz progressive 
           mode 6: 640x480 @ 75Hz 4:3, clock:31MHz progressive 
           mode 8: 800x600 @ 56Hz 4:3, clock:36MHz progressive 
           mode 9: 800x600 @ 60Hz 4:3, clock:40MHz progressive 
           mode 10: 800x600 @ 72Hz 4:3, clock:50MHz progressive 
           mode 11: 800x600 @ 75Hz 4:3, clock:49MHz progressive 
           mode 16: 1024x768 @ 60Hz 4:3, clock:65MHz progressive 
           mode 17: 1024x768 @ 70Hz 4:3, clock:75MHz progressive 
           mode 18: 1024x768 @ 75Hz 4:3, clock:78MHz progressive 
           mode 21: 1152x864 @ 75Hz 4:3, clock:108MHz progressive 
           mode 28: 1280x800 @ 60Hz 16:10, clock:83MHz progressive 
           mode 35: 1280x1024 @ 60Hz 5:4, clock:108MHz progressive 
           mode 36: 1280x1024 @ 75Hz 5:4, clock:135MHz progressive 
           mode 47: 1440x900 @ 60Hz 16:10, clock:106MHz progressive 
           mode 58: 1680x1050 @ 60Hz 16:10, clock:146MHz progressive 
           mode 83: 1600x900 @ 60Hz 16:9, clock:108MHz progressive 
           mode 85: 1280x720 @ 60Hz 16:9, clock:74MHz progressive 
root@rpi4:/opt/vc/bin# ./tvservice -m DMT -v 7
Group DMT has 18 modes:
           mode 4: 640x480 @ 60Hz 4:3, clock:25MHz progressive 
           mode 5: 640x480 @ 72Hz 4:3, clock:31MHz progressive 
           mode 6: 640x480 @ 75Hz 4:3, clock:31MHz progressive 
           mode 8: 800x600 @ 56Hz 4:3, clock:36MHz progressive 
           mode 9: 800x600 @ 60Hz 4:3, clock:40MHz progressive 
           mode 10: 800x600 @ 72Hz 4:3, clock:50MHz progressive 
           mode 11: 800x600 @ 75Hz 4:3, clock:49MHz progressive 
           mode 16: 1024x768 @ 60Hz 4:3, clock:65MHz progressive 
           mode 17: 1024x768 @ 70Hz 4:3, clock:75MHz progressive 
           mode 18: 1024x768 @ 75Hz 4:3, clock:78MHz progressive 
           mode 21: 1152x864 @ 75Hz 4:3, clock:108MHz progressive 
           mode 28: 1280x800 @ 60Hz 16:10, clock:83MHz progressive 
           mode 35: 1280x1024 @ 60Hz 5:4, clock:108MHz progressive 
           mode 36: 1280x1024 @ 75Hz 5:4, clock:135MHz progressive 
           mode 47: 1440x900 @ 60Hz 16:10, clock:106MHz progressive 
           mode 58: 1680x1050 @ 60Hz 16:10, clock:146MHz progressive 
           mode 83: 1600x900 @ 60Hz 16:9, clock:108MHz progressive 
           mode 85: 1280x720 @ 60Hz 16:9, clock:74MHz progressive 
root@rpi4:/opt/vc/bin# ./tvservice -s -v 2
state 0xa [HDMI CUSTOM RGB lim 16:9], 1920x1080 @ 60.00Hz, progressive
root@rpi4:/opt/vc/bin# ./tvservice -s -v 7
state 0xa [HDMI CUSTOM RGB lim 16:9], 1920x1080 @ 60.00Hz, progressive
root@rpi4:/opt/vc/bin#

Xrandr produces an error message and only detects one monitor:

Code:

root@rpi4:/opt/vc/bin# cat /tmp/xrandr.log 
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected 1920x1080+0+0 0mm x 0mm
   1920x1080      0.00* 
root@rpi4:/opt/vc/bin#

louigi600 · 03-11-2021, 05:40 AM

Am I the only loony that wants to connect 2 displays on the RPi4 running slackware ?

enine · 03-14-2021, 10:36 PM

I just tried on my Pi400 and get the same results. I can get a duplicate on both monitors because xrandr thinks there is only one

louigi600 · 03-21-2021, 12:03 PM

I did a little experiment today and now apparently the 2 displays are now working right on my RPi4 with current.
I started off with doing the update, hoping that it would bring some fix. Unfortunately after the update everything looked the same: xrandr outputting a warning and only one display detected, also odd black background instead of the default gray fluxbox background output duplicated on both display.

So I started thinking maybe it's an issue with xorg.conf so I removed the default one that was there (so that X would autodetect properly) restarted X ... low and behold the background is now ok and by default second display is set to be an extension right of first display. Very good ... Last time I was using 2 monitors on a Slackware system I remember having to tinker to get it to do this: now it's doing the most sensible thing by default.
Very nice.

alekow · 03-21-2021, 03:50 PM

Hi Louigi,

Thanks for this thread, it turns out deleting xorg.conf solved the issue on my chromebook too. What it did was changing the xorg display driver from fbturbo to default fbdev. Not only it fixed hdmi display for me, also it made video playback on a well known website behaving as it should, even in full HD. Which means it now works better than on chrome OS on this device.

Regards,
Alex

enine · 03-25-2021, 04:21 PM

I renamed /etc/X11/xorg.conf.d and nothing changed
renamed the xorg.conf.d in /usr/local/X11 and X froze after starting.
I notice that rasbian switched to dual somewhere in the middle of the boot process, as the second monitor will switch from the color screen to text then.

louigi600 · 03-25-2021, 04:47 PM

It's not the folder you need to remove or rename, just get rid of /etc/X11/xorg.conf or maybe /etc/X11/xorg.conf.d/xorg.conf
Have you edited /boot/config.txt ? You will get nothing unill you put something like this in there:
max_framebuffers=2

enine · 03-25-2021, 06:59 PM

ohh, wow, non thinking moment, ok, put the folders back and deleted the xorg.conf. I had forgotten I overwrote my Slackware SD card when I was messing with berryboot and so when I installed Slackware again I forgot yo edit the boot/config.txt.

I am working now

For search purposes. Raspberry Pi 400 Slackware works with Dual monitors.