dankcushions
Posts: 27
Joined: Sat Jun 13, 2015 10:40 am

Raspberry Pi 4B: Disable ALL 4k modes?

Mon Nov 04, 2019 10:40 am

Hi,

By default if you connect a Pi4 to a 4k display, the EDID handshake will pick a 4Kp30 display mode (which can be modified to 4Kp60 via a config.txt change). This makes sense as you typically want to use the 'best' display mode supported by your display. However, in certain contexts, 4k is just too intense for the pi - for example: 3d/gaming.

Is there a way of still using the EDID automatic display mode selection, but forgoing the 4K modes? eg, if i was connected to a 4k display it would use 1080p60 instead.

I realise you can force a specific display mode, but I don't want to presume anything about the display I'm going to connect to, in case it doesn't support the mode I pick.

The context of this is for Retropie - currently we require 4k display users to manually force the appropriate <=1080p display mode since a lot of the software just uses the full display resolution (which is a slide-show at 4k). It would be nicer to make the EDID handshake only pick <=1080p. the long term approach will be to fix the software so it doesn't display at 4k.

Thanks!

timg236
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: Raspberry Pi 4B: Disable ALL 4k modes?

Mon Nov 04, 2019 10:57 am

The pixel frequency is used by the firmware and KMS to filter HDMI modes. Something like this would filter out 4Kp30 but you may want to tweak it according to the set of < 4K modes that you want to enable

[hdmi:0]
hdmi_max_pixel_freq=200000000

[hdmi:1]
hdmi_max_pixel_freq=200000000

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: Raspberry Pi 4B: Disable ALL 4k modes?

Mon Nov 04, 2019 11:31 am

Or slightly more concisely

Code: Select all

hdmi_max_pixel_freq:0=200000000
hdmi_max_pixel_freq:1=200000000
1080p[50|60] have a 148.5MHz pixel clock.
1080p[24|25|30] have a 74.25MHz pixel clock.
See https://en.wikipedia.org/wiki/Extended_ ... _Version_3 section "CEA/EIA-861 standard resolutions and timings" for a complete list of the standard timings.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
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beta-tester
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Location: de_DE

Re: Raspberry Pi 4B: Disable ALL 4k modes?

Wed Dec 11, 2019 8:09 am

i just used those limiting options instead of disabling HDMI EDID, because i had issues with UI scaling under VLC media player before.
but now i have issued with VNC- when i connect me to the RPi4, it captures the screen with 4k, even the RPi4's desktop is only 1920x1080.
{ I only give negative feedback }
RPi B (256MB), B (512MB), B+, ZeroW; 2B; 3B, 3B+; 4B (4GB)

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