Flickering VGA output at 720p/1080p on 'TDX Wayland with XWayland 5.3.0+build.10 (dunfell)'

imx8x Modules have HW Version 1.0D, I’ve tested 2 of them.

On Colibri Eval V3.2{A,B} I get various amounts of flickering on VGA output depending on used resolution.

I’m testing with glmark2-es2-{wayland,drm} and gstreamer either directly on drm or via wayland/drm in the official image (see below) and a custom-built one based on buildroot (kernel 5.4.129 from toradex_5.4-2.3.x-imx). Both images show the exact same behaviour.

I’m still waiting for my DSI-HDMI adapter, I thus cannot tell whether the flickering comes from the VGA conversion chip or already happens earlier in the graphics pipeline.

The imx6dl never had a problem with flickering at 720p and 1080p on the same eval boards. But it is much slower and runs its graphics at less FPS.

  • With default display-vga_overlay.dtbo (640x480) there are no flickers.
  • With display-fullhd_overlay.dtbo (1080p) there is massive flickering (all the time)
  • With a custom DT overlay (720p) there is some flickering (depending on which test glmark2 is running).

Anybody else having the same issues and knowing the cure? Are there any limits on the VGA conversion chip I am stumbling upon here and everything will be fine with LVDS/DSI/HDMI output?

official image (Toradex Embedded Linux Reference Multimedia Image for V1.0B HW)
# cat /etc/os-release 
NAME="TDX Wayland with XWayland"
VERSION="5.3.0+build.10 (dunfell)"
PRETTY_NAME="TDX Wayland with XWayland 5.3.0+build.10 (dunfell)"

custom image
# uname -a
Linux gtv-imx8 5.4.129 #2 SMP PREEMPT Wed Aug 18 17:58:09 CEST 2021 aarch64 GNU/Linux

# glmark2-es2-wayland
    glmark2 2020.04
    OpenGL Information
    GL_VENDOR:     Vivante Corporation
    GL_RENDERER:   Vivante GC7000L
    GL_VERSION:    OpenGL ES 3.1 V6.4.3.p1.305572

Hello @ventosys and Welcome to the Toradex Community!

I did the same tests with FullHD Resolution and I can reproduce the flickering. As you already thought, this is a limitation of the RGB to VGA Conversion Chip. Using DSI-HDMI adapter, you should not see this flickering.

By the way, what was the value of FPS on iMX6?

Best regards,

By the way, what was the value of FPS on iMX6?

Well, the VGA output on the imx6dl was configured with 60Hz, but the glmark benchmarks were running always considerably below 60Hz.

Video playback via gstreamer was fine though at fullhd resolution and refresh rate. So maybe it’s not just the VGA conversion chip, afterall.

display timings for imx6dl

&lcd_display {
	status = "okay";

	interface-pix-fmt = "bgr666";
	display-timings {
			hactive = <1920>;
			vactive = <1080>;

			hfront-porch = <328>;
			hback-porch = <128>;
			vfront-porch = <32>;
			vback-porch = <3>;
			hsync-len = <200>;
			vsync-len = <5>;

			clock-frequency = <173010380>; /* 1 / 5780e-12 */

			vsync-active = <1>; /* 0: active low, 1: active high */


Could you let us know once you get the HDMI adapter if you still see the issue?

Thanks and best regards,

With the HDMI adapter, there is no flickering at 720p/1080p.

This kind of solves my issue.