Change resolution using bash on rpi4?

domb84 · December 29, 2021 at 10:33 PM

I've been searching for some time for a way to set the resolution via bash on libreelec but cannot find anything. Is there a method for setting it?

I've tried the following...

Code

LibreELEC:~ # echo U:1920x1200p-0 > /sys/class/graphics/fb0/mode
sh: write error: Invalid argument

Code

LibreELEC:~ # tvservice -e "CEA 4"
tvservice is not supported when using the vc4-kms-v3d driver.
Similar features are available with standard linux tools
such as modetest from libdrm-tests.

Code

LibreELEC:~ # xrandr -s 1920x1080
-sh: xrandr: not found

Code

LibreELEC:~ # fbset -s

mode "1920x1080-0"
        # D: 0.000 MHz, H: 0.000 kHz, V: 0.000 Hz
        geometry 1920 1080 1920 1080 16
        timings 0 0 0 0 0 0 0
        accel true
        rgba 5/11,6/5,5/0,0/0
endmode

Finally found some good documentation for modetest but that also fails with permission denied:

DRM KMS overview - stm32mpu

Code

LibreELEC:~ # modetest -M vc4 -s 32@76:1280x720-50 -d
setting mode 1280x720-50.00Hz on connectors 32, crtc 76
failed to set mode: Permission denied

This appears to be down to DRM. Is there a way to disable this?

Code

LibreELEC:~ # dmesg | grep drm -i
[    1.379393] vc4-drm gpu: bound fe400000.hvs (ops 0xffffffc010d21850)
[    1.527982] vc4-drm gpu: bound fe400000.hvs (ops 0xffffffc010d21850)
[    1.533437] vc4-drm gpu: bound fef00700.hdmi (ops 0xffffffc010d1f7d8)
[    1.535515] vc4-drm gpu: bound fef05700.hdmi (ops 0xffffffc010d1f7d8)
[    1.535673] vc4-drm gpu: bound fe004000.txp (ops 0xffffffc010d21f98)
[    1.535801] vc4-drm gpu: bound fe206000.pixelvalve (ops 0xffffffc010d1d020)
[    1.535913] vc4-drm gpu: bound fe207000.pixelvalve (ops 0xffffffc010d1d020)
[    1.536031] vc4-drm gpu: bound fe20a000.pixelvalve (ops 0xffffffc010d1d020)
[    1.536118] vc4-drm gpu: bound fe216000.pixelvalve (ops 0xffffffc010d1d020)
[    1.536226] vc4-drm gpu: bound fec12000.pixelvalve (ops 0xffffffc010d1d020)
[    1.537809] [drm] Initialized vc4 0.0.0 20140616 for gpu on minor 0
[    1.589195] vc4-drm gpu: [drm] The core clock cannot reach frequencies high enough to support 4k @ 60Hz.
[    1.589203] vc4-drm gpu: [drm] Please change your config.txt file to add hdmi_enable_4kp60.
[    1.651925] vc4-drm gpu: [drm] fb0: vc4drmfb frame buffer device
[    1.689585] [drm] Initialized v3d 1.0.0 20180419 for fec00000.v3d on minor 1
[    5.001828] systemd[1]: Starting Load Kernel Module drm...
[    5.111256] systemd[1]: modprobe@drm.service: Succeeded.
[    5.111821] systemd[1]: Finished Load Kernel Module drm.

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Any ideas? I need a tool for an add on wrapper to launch script. Thanks!

**chewitt** · December 30, 2021 at 4:59 AM

You cannot switch resolutions like you can with xrandr (which doesn't work as we don't use X11) but you can force the intitial resolution used for boot by adding "video=HDMI-A-1:1920x1080M@60" to kernel boot params. On a Raspberry Pi this is in cmdline.txt in the root folder of the SD card. From SSH this is /flash/cmdline.txt but you will need to remount /flash in rw mode first to edit the file.

domb84 · December 30, 2021 at 8:41 AM

Quote from chewitt

You cannot switch resolutions like you can with xrandr (which doesn't work as we don't use X11) but you can force the intitial resolution used for boot by adding "video=HDMI-A-1:1920x1080M@60" to kernel boot params. On a Raspberry Pi this is in cmdline.txt in the root folder of the SD card. From SSH this is /flash/cmdline.txt but you will need to remount /flash in rw mode first to edit the file.

I'm already aware of the boot parameters but this doesn't suit my use case. I need different resolutions for different applications.

Kodi already switches resolution and frame rate based on source material, can I emulate this some how? I've been searching through the source code but cannot find anything regarding how this is achieved (also my knowledge beyond bash and a bit of python is poor!).

It seems modetest does actually work if I stop the kodi service, so I'll see if I can shoehorn that into a script somehow.

**chewitt** · December 30, 2021 at 8:48 AM

Kodi calls the kernel DRM APIs to perform modeset, so Kodi itself doesn't change the mode, the kenel does; it's an abstracted process.

Change resolution using bash on rpi4?

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