Should fallback to other providers when kgsl not available

[lool]

Hi

After trying kgsl + adreno on a hamoa laptop (not yet working :)), I removed just the kgsl part and left adreno libs installed (adreno-egl1, adreno-gles2, adreno-gles1, adreno-common) – and rebooted.

After that, I was expecting my system would start with freedreno, and work normally. However gdm couldn't start, and neither could weston until I had removed the adreno-* packages (I left libgbm-msm1 with no consequence).

I'm not sure which one was the culprit, nor where the exact fallback should be, but I believe our EGL or GLES implementations should graciously exit if they miss dependencies such as kgsl, and let the next provider deliver (likely mesa/freedreno).

I'm attaching two logs of running weston, both with libgbm, one with adreno packages, the other one without.

weston-with-gbm-msm-and-adreno.log.txt
weston-working-with-msm-gbm-without-adreno.log.txt

[maheshangadi95]

Removing only KGSL is not sufficient to fall back to Mesa/Freedreno.

Even without the KGSL kernel driver, the GLVND EGL loader still discovers and loads the Adreno EGL vendor library through 10_adreno.json, which is installed by the qcom-adreno packages. Since this ICD file has a higher priority than Mesa's ICD, EGL continues to select the Adreno implementation first.

As a result, the system never reaches the Mesa/Freedreno EGL stack, due to this Weston fail during EGL initialization.

To force Mesa/Freedreno, either:

export __EGL_VENDOR_LIBRARY_FILENAMES=/usr/share/glvnd/egl_vendor.d/50_mesa.json

or remove the Adreno EGL vendor file: /usr/share/glvnd/egl_vendor.d/10_adreno.json

With the Mesa ICD selected, the system should use the DRM kernel driver and Mesa/Freedreno userspace stack normally.