slapplebags
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dual vertical 4k monitors possible on RPI 4?

Mon Nov 18, 2019 4:23 am

Is it possible to run dual 4k monitors at 3840*2160 or 4096*2160? Poking around in the GUI settings it doesnt look like its possible on the RPI 4.

W. H. Heydt
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Re: dual vertical 4k monitors possible on RPI 4?

Mon Nov 18, 2019 4:51 am

You should be able to rotate the images.

slapplebags
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Re: dual vertical 4k monitors possible on RPI 4?

Mon Nov 18, 2019 6:56 pm

Yes I can rotate the image, but i cannot set the resolution to anything above 1920*1080 when the images are rotated.

jamesh
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Re: dual vertical 4k monitors possible on RPI 4?

Mon Nov 18, 2019 10:45 pm

slapplebags wrote:
Mon Nov 18, 2019 6:56 pm
Yes I can rotate the image, but i cannot set the resolution to anything above 1920*1080 when the images are rotated.
Hmm, are you using the FKMS driver or have you reverted to legacy graphics by commenting out the FKMS line in config.txt
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slapplebags
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Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 12:10 am

I'm using whatever the default is, I havent touched the config.txt yet.

A bit of backstory may be helpful, this is a digital menu for a local bar running on a pair of 4k samsung TVs, with a chromium instance running on each monitor. The panels are setup vertically, and while 1920x1080 works it leaves a black border around the image and the panels helpfully dont have a way to change the resolution to 1920x1080. Both displays are connected via HDMI with no converters or anything in between. Model is raspberry pi 4 with 4GB of RAM.

After getting it working i wiped and reinstalled with a fresh noobs image to remove stuff i put on their while getting it figured out. I ran all updates and only changes are installing unclutter and adding the commands to lxsession to open the chromium instances on each monitor and navigate to a webpage.

I'm going to work on it this evening so i'll include some screenshots of what i'm seeing.

slapplebags
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Joined: Mon Nov 18, 2019 4:20 am

Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 4:07 am

attached is the error i get when trying to set both displays to vertical and 4k via the GUI. Tried setting it in /boot/config.txt with rotate_display=1 but that only rotated one display.
Attachments
Screen Shot 2019-11-18 at 7.55.22 PM.png
Screen Shot 2019-11-18 at 7.55.22 PM.png (164.65 KiB) Viewed 1438 times

slapplebags
Posts: 8
Joined: Mon Nov 18, 2019 4:20 am

Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 4:52 am

after a reboot i can now get 3480*2160 working so thats closer, 4k results in black screens.

slapplebags
Posts: 8
Joined: Mon Nov 18, 2019 4:20 am

Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 5:38 am

issue is resolved, upping gpu_ram in config.txt and adding cma=512 to cmdline.txt resolved the issue.

6by9
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Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 6:38 am

Curious as I know I tested rotated dual 4k prior to release and it didn't need more than the standard 256MB of cma.

Increasing gpu_mem is likely to be counter productive as it takes more memory away from the arm, and gpu mem is now only used for things like the camera and codecs.

Cma and gpu_mem combined must be less than 1G, otherwise you'll find the system won't boot.

Note that X does transpose as a second pass of composition, and uses the 3d hardware again to do so, so there is a significant increase in 3d load which will make the system feel a little sluggish.
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slapplebags
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Joined: Mon Nov 18, 2019 4:20 am

Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 5:07 pm

Ah, thanks for the follow up, I'll remove the gpu_mem setting. And yes it certainly does feel sluggish. Running 2 instances of chromium takes about 30 seconds to fully launch and render.

jamesh
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Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 5:10 pm

slapplebags wrote:
Tue Nov 19, 2019 5:07 pm
Ah, thanks for the follow up, I'll remove the gpu_mem setting. And yes it certainly does feel sluggish. Running 2 instances of chromium takes about 30 seconds to fully launch and render.
It should only be the rendering that is affected - 30s sounds a bit long. But you are running two. Maybe a faster SD card would help.
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slapplebags
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Joined: Mon Nov 18, 2019 4:20 am

Re: dual vertical 4k monitors possible on RPI 4?

Tue Nov 19, 2019 11:15 pm

I'm not too concerned about the loading time as it's a fairly static menu. If they wanted it to do something fancy then it might be an issue. I currently have a samsung Evo select 32gb sd card which claims to do 90mbps read and 20 write.

I haven't had a chance to remove the GPU setting yet but I'll report back when I do.

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