Mpv: [vo/gpu/wayland] glGetString(GL_VERSION) returned NULL

[Elyotna]

mpv version and platform

mpv 0.29.0 on Ubuntu 18.04 arm64. Wayland desktop. Also tested with mpv-git.
Board: Le Potato (Cortex A-53 + Mali-450)
Using the binary drivers for the Mali, enabling GLES 2.0

Reproduction steps

mpv -v --vo=gpu --gpu-context=wayland --opengl-es=yes input.mp4

Expected behavior

The call to glGetString doesn't return NULL. Note that on the same configuration, I can run glmark2-es2-wayland and it works fine (including its call to glGetString, it reads out the Mali vendor strings, etc.).

libre@libre-computer-board:~$ glmark2-es2-wayland
=======================================================
    glmark2 2014.03+git20150611.fa71af2d
=======================================================
    OpenGL Information
    GL_VENDOR:     ARM
    GL_RENDERER:   Mali-450 MP
    GL_VERSION:    OpenGL ES 2.0
=======================================================

Actual behavior

[vo/gpu/wayland] glGetString(GL_VERSION) returned NULL.

Log file

https://0x0.st/sUiE.txt

[Hrxn]

Board: Le Potato (Cortex A-53 + Mali-450)

I first thought this was a joke. But no, it's actual real hardware. Great name.

[Elyotna]

I dug a bit more into this, and it's the call to eglMakeCurrent(p->egl_display, NULL, NULL, p->egl_context) in context_wayland.c that fails with error EGL_BAD_MATCH. There's no error-guard around the call so it kept going forward to glGetString.

Still trying to see exactly what's wrong but nothing jumps out so far.

[Elyotna]

"Fixed" it by calling egl_create_window(ctx) (had to set default geometry values since they were at 0 for the window creation), removing the call to eglMakeCurrent(p->egl_display, NULL, NULL, p->egl_context).

I'm guessing the mali blob for wayland doesn't like having NULL surfaces in its eglMakeCurrent implementation.

[brankod]

This is also a still present issue on zynqmp based devices (mali 400MP).

[ghost]

This probably warrants checking the code to see whether it's a driver bug or a mistake in the mpv code.

[Dudemanguy]

It's hard to say what the problem is. Just glancing at Khronos¹, this one looks like the most likely one to me.

If context does not support being bound without read and draw surfaces, and both draw and read are EGL_NO_SURFACE, an EGL_BAD_MATCH error is generated.

Perhaps the real solution is #6240?