I'm using a custom board/custom distro, based on yocto Dunfell. It's using vivante drivers (so not etnaviv).
Running kernel is: 5.4-2.1.x-imx
X11 itself is working fine. Although I get a VivDRIScreenInit -releated error message in the log:

X.Org X Server 1.20.8

X Protocol Version 11, Revision 0

[    34.528] Build Operating System: Linux 

[    34.528] Current Operating System: Linux imx6qtelevic_generic 5.4.46-04202-gd069a637b280 #15 SMP PREEMPT Wed Oct 14 12:13:42 CEST 2020 armv7l

[    34.528] Kernel command line: version=DEV_33968064_1-04-02 console=ttymxc3,115200 ubi.mtd=0 root=ubi0:rootfsA rootfstype=ubifs mtdparts=gpmi-nand:-(ubipart) quiet

[    34.528] Build Date: 29 March 2020  08:21:46PM

[    34.528]  

[    34.534] Current version of pixman: 0.38.4

[    34.535] Before reporting problems, check http://wiki.x.org

to make sure that you have the latest version.

[    34.535] Markers: (--) probed, (**) from config file, (==) default setting,

(++) from command line, (!!) notice, (II) informational,

(WW) warning, (EE) error, (NI) not implemented, (??) unknown.

[    34.538] (==) Log file: "/var/log/Xorg.0.log", Time: Fri Mar  9 12:41:08 2018

[    34.565] (==) Using config file: "/etc/X11/xorg.conf"

[    34.566] (==) Using system config directory "/usr/share/X11/xorg.conf.d"

[    34.574] (==) No Layout section.  Using the first Screen section.

[    34.576] (==) No screen section available. Using defaults.

[    34.576] (**) |-->Screen "Default Screen Section" (0)

[    34.576] (**) |   |-->Monitor "<default monitor>"

[    34.584] (==) No device specified for screen "Default Screen Section".

Using the first device section listed.

[    34.584] (**) |   |-->Device "i.MX Accelerated Framebuffer Device"

[    34.584] (==) No monitor specified for screen "Default Screen Section".

Using a default monitor configuration.

[    34.585] (**) Option "BlankTime" "0"

[    34.585] (**) Option "StandbyTime" "0"

[    34.585] (**) Option "SuspendTime" "0"

[    34.585] (**) Option "OffTime" "0"

[    34.586] (==) Automatically adding devices

[    34.586] (==) Automatically enabling devices

[    34.586] (==) Automatically adding GPU devices

[    34.588] (==) Max clients allowed: 256, resource mask: 0x1fffff

[    34.589] (WW) The directory "/usr/share/fonts/X11/misc/" does not exist.

[    34.589] Entry deleted from font path.

[    34.590] (WW) The directory "/usr/share/fonts/X11/TTF/" does not exist.

[    34.590] Entry deleted from font path.

[    34.590] (WW) The directory "/usr/share/fonts/X11/OTF/" does not exist.

[    34.590] Entry deleted from font path.

[    34.590] (WW) The directory "/usr/share/fonts/X11/Type1/" does not exist.

[    34.590] Entry deleted from font path.

[    34.590] (WW) The directory "/usr/share/fonts/X11/100dpi/" does not exist.

[    34.590] Entry deleted from font path.

[    34.590] (WW) The directory "/usr/share/fonts/X11/75dpi/" does not exist.

[    34.590] Entry deleted from font path.

[    34.590] (==) FontPath set to:

 

[    34.591] (==) ModulePath set to "/usr/lib/xorg/modules"

[    34.591] (II) The server relies on udev to provide the list of input devices.

If no devices become available, reconfigure udev or disable AutoAddDevices.

[    34.600] (II) Loader magic: 0x5f8d80

[    34.600] (II) Module ABI versions:

[    34.600] X.Org ANSI C Emulation: 0.4

[    34.601] X.Org Video Driver: 24.1

[    34.601] X.Org XInput driver : 24.1

[    34.601] X.Org Server Extension : 10.0

[    34.610] (II) no primary bus or device found

[    34.614] (II) LoadModule: "glx"

[    34.630] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so

[    34.793] (II) Module glx: vendor="X.Org Foundation"

[    34.794] compiled for 1.20.8, module version = 1.0.0

[    34.794] ABI class: X.Org Server Extension, version 10.0

[    34.797] (II) LoadModule: "vivante"

[    34.798] (II) Loading /usr/lib/xorg/modules/drivers/vivante_drv.so

[    34.809] (II) Module vivante: vendor="X.Org Foundation"

[    34.809] compiled for 1.20.8, module version = 1.0.0

[    34.810] ABI class: X.Org Video Driver, version 24.1

[    34.812] (II) VIVANTE: fb driver for vivante: VivanteGC500, VivanteGC2100,

VivanteGCCORE

[    34.814] (--) using VT number 3

 

[    34.830] (WW) Falling back to old probe method for vivante

[    34.831] (II) Loading sub module "fbdevhw"

[    34.831] (II) LoadModule: "fbdevhw"

[    34.832] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so

[    34.842] (II) Module fbdevhw: vendor="X.Org Foundation"

[    34.843] compiled for 1.20.8, module version = 0.0.2

[    34.843] ABI class: X.Org Video Driver, version 24.1

[    34.843] (II) VIVANTE(0): using default device

[    34.849] (WW) VGA arbiter: cannot open kernel arbiter, no multi-card support

[    34.857] (II) VIVANTE(0): Device preferred mode 'fb0':U:1280x800p-59 

[    34.857] (II) VIVANTE(0): Creating default Display subsection in Screen section

"Default Screen Section" for depth/fbbpp 24/32

[    34.858] (==) VIVANTE(0): Depth 24, (==) framebuffer bpp 32

[    34.858] (==) VIVANTE(0): RGB weight 888

[    34.858] (==) VIVANTE(0): Default visual is TrueColor

[    34.858] (==) VIVANTE(0): Using gamma correction (1.0, 1.0, 1.0)

[    34.858] (DB) xf86MergeOutputClassOptions unsupported bus type 0

[    34.858] (**) VIVANTE(0): mExaHwType:1

[    34.858] (II) VIVANTE(0): checking modes against framebuffer device...

[    34.858] (II) VIVANTE(0): checking modes against monitor...

[    34.858] (II) VIVANTE(0): Virtual size is 0x0 (pitch 0)

[    34.858] (==) VIVANTE(0): DPI set to (96, 96)

[    34.858] (II) Loading sub module "fb"

[    34.859] (II) LoadModule: "fb"

[    34.859] (II) Loading /usr/lib/xorg/modules/libfb.so

[    34.889] (II) Module fb: vendor="X.Org Foundation"

[    34.889] compiled for 1.20.8, module version = 1.0.0

[    34.889] ABI class: X.Org ANSI C Emulation, version 0.4

[    34.889] (II) Loading sub module "exa"

[    34.889] (II) LoadModule: "exa"

[    34.889] (II) Loading /usr/lib/xorg/modules/libexa.so

[    34.894] (II) Module exa: vendor="X.Org Foundation"

[    34.894] compiled for 1.20.8, module version = 2.6.0

[    34.894] ABI class: X.Org Video Driver, version 24.1

[    35.200] (II) VIVANTE(0): printing discovered frame buffer 'fb0' supported modes:

[    35.202] (II) VIVANTE(0): Modeline "U:1280x800p-59"x0.0   71.10  1280 1320 1400 1440  800 803 813 823 -hsync -vsync -csync (49.4 kHz eP)

[    35.236] (II) VIVANTE(0): Output DISP3 BG has no monitor section

[    35.237] (II) VIVANTE(0): Printing probed modes for output DISP3 BG

[    35.237] (II) VIVANTE(0): Modeline "U:1280x800p-59"x60.0   71.10  1280 1320 1400 1440  800 803 813 823 -hsync -vsync -csync (49.4 kHz eP)

[    35.238] (II) VIVANTE(0): Output DISP3 BG connected

[    35.238] (II) VIVANTE(0): Using exact sizes for initial modes

[    35.239] (II) VIVANTE(0): Output DISP3 BG using initial mode U:1280x800p-59 +0+0

[    35.239] (II) VIVANTE(0): imxDisplayPreInit: virtual set 1280 x 800, display width 0

[    35.239] (II) VIVANTE(0): VivPreInit: adjust display width 1280

[    35.321] (II) VIVANTE(0): reserve 8355840 bytes for on screen frame buffer; total fb memory size 16721920 bytes; offset of shadow buffer 8355840

[    35.414] (II) VIVANTE(0): hardware: DISP3 BG (video memory: 16330kB)

[    35.472] (II) VIVANTE(0): FB Start = 0xb55c4000  FB Base = 0xb55c4000  FB Offset = (nil)

[    35.484] (II) VIVANTE(0): test Initializing EXA

[    35.606] (II) EXA(0): Driver allocated offscreen pixmaps

[    35.607] (II) EXA(0): Driver registered support for the following operations:

[    35.607] (II)         Solid

[    35.607] (II)         Copy

[    35.607] (II)         Composite (RENDER acceleration)

[    35.607] (II)         UploadToScreen

[    35.609] (==) VIVANTE(0): Backing store enabled

[    35.627] (==) VIVANTE(0): DPMS enabled

[    35.704] (EE) VIVANTE(0): [dri] VivDRIScreenInit failed because Drm can't be opened.

[    35.705] (II) Initializing extension Generic Event Extension

[    35.708] (II) Initializing extension SHAPE

[    35.709] (II) Initializing extension MIT-SHM

[    35.709] (II) Initializing extension XInputExtension

[    35.713] (II) Initializing extension XTEST

[    35.715] (II) Initializing extension BIG-REQUESTS

[    35.715] (II) Initializing extension SYNC

[    35.718] (II) Initializing extension XKEYBOARD

[    35.721] (II) Initializing extension XC-MISC

[    35.721] (II) Initializing extension XFIXES

[    35.722] (II) Initializing extension RENDER

[    35.724] (II) Initializing extension RANDR

[    35.724] (II) Initializing extension COMPOSITE

[    35.726] (II) Initializing extension DAMAGE

[    35.728] (II) Initializing extension MIT-SCREEN-SAVER

[    35.728] (II) Initializing extension DOUBLE-BUFFER

[    35.729] (II) Initializing extension DPMS

[    35.729] (II) Initializing extension Present

[    35.730] (II) Initializing extension DRI3

[    35.732] (II) Initializing extension X-Resource

[    35.732] (II) Initializing extension XVideo

[    35.733] (II) Initializing extension XVideo-MotionCompensation

[    35.734] (II) Initializing extension GLX

[    35.752] (II) AIGLX: Screen 0 is not DRI2 capable

[    36.443] (II) IGLX: Loaded and initialized swrast

[    36.444] (II) GLX: Initialized DRISWRAST GL provider for screen 0

[    36.444] (II) Initializing extension XFree86-VidModeExtension

[    36.445] (II) Initializing extension XFree86-DGA

[    36.445] (II) Initializing extension XFree86-DRI

[    36.447] (II) Initializing extension DRI2

[    36.447] (II) Initializing extension vivext

[    36.450] (II) VIVANTE(0): Setting screen physical size to 338 x 211

root@imx6qtelevic_generic:/lib/modules# DISPLAY=:0 gst-launch-1.0 videotestsrc ! imxeglvivsink

Setting pipeline to PAUSED ...

Xlib:  extension "XFree86-DRI" missing on display ":0".

Pipeline is PREROLLING ...

Xlib:  extension "XFree86-DRI" missing on display ":0".

Xlib:  extension "XFree86-DRI" missing on display ":0".

Pipeline is PREROLLED ...

Setting pipeline to PLAYING ...

New clock: GstSystemClock

Caught SIGSEGV

#0  0x76bdebe4 in ?? () from /lib/libc.so.6

#1  0x76c57744 in poll () from /lib/libc.so.6

#2  0x76d66bfa in ?? () from /usr/lib/libglib-2.0.so.0

Spinning.  Please run 'gdb gst-launch-1.0 694' to continue debugging, Ctrl-C to quit, or Ctrl-\ to dump core.

^Chandling interrupt.

Interrupt: Stopping pipeline ...

Execution ended after 0:03:45.501871360

Setting pipeline to PAUSED ...

Setting pipeline to READY ...

Setting pipeline to NULL ...