LinuxQuestions.org - [SOLVED] Dual monitor on RPi4

- Slackware - ARM (https://www.linuxquestions.org/questions/slackware-arm-108/)

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Dual monitor on RPi4

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.

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

@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.

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.

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#

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

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

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.

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

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.

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

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.

I renew this thread since I cannot make the dual HDMI outputs work correctly.

I have put

dtoverlay=vc4-fkms-v3d
max_framebuffers=2

in /boot/config.txt

I have also rename my xorg.conf to old_xorg.conf to let X autodetect the outputs

When I plug an HDMI cable from my Diskio PI ( connected to a HDMI port of the RPI 4 ) to a computer screen :

- I see nothing on the computer screen
- All the screen is compressed to a little window in the upper left corner : here xrandr sees only this window in 640x480 and nothing else

Looking at the log of X it seems there is a lack of EDID data. But these data are made by tvservice on Raspian.

@louigi600 is your /opt/vc package available somewhere ?

what other settings do you have in the config.txt

Code:

# Uncomment if you get no picture on HDMI for a default "safe" mode

#hdmi_safe=1



# Uncomment this if your display has a black border of unused pixels visible

# and your display can output without overscan

disable_overscan=1



# Uncomment the following to adjust overscan. Use positive numbers if console

# goes off screen, and negative if there is too much border

#overscan_left=16

#overscan_right=16

#overscan_top=16

#overscan_bottom=16



# Uncomment to force a console size. By default it will be display's size minus

# overscan.

#framebuffer_width=1280

#framebuffer_height=720



# Uncomment if hdmi display is not detected and composite is being output

#hdmi_force_hotplug=1



# Uncomment to force a specific HDMI mode (this will force VGA)

#hdmi_group=1

#hdmi_mode=1



# Uncomment to force a HDMI mode rather than DVI. This can make audio work in

# DMT (computer monitor) modes

hdmi_drive=2



# Uncomment to increase signal to HDMI, if you have interference, blanking, or

# no display

#config_hdmi_boost=4

Once X is running it's late to plug the monitor in. You need to have it plugged in before X starts.
Once X has detected 2 monitors you can unplug one and re-plug it (and with luck it will still work).
I forgot exactly what I put in my config.txt but if need be I can share it.
On the RPi4 I generally have both displays plugged in at boot time and you should see the text console duplicated on both as the system boots.