vkkhrdisplay wayland : Only CPU rendering on Vulkan

I am trying to achieve a setup with a QTWayland compositor using Vulkan (RHI) and vkkhrdisplay (QPA), and running QtQuick programs upon Vulkan (RHI). Here are the environnement variables I use :

General :

• EGL_LOG_LEVEL=debug
• QSG_INFO=1
• QSG_RHI_DEBUG_LAYER=1

Compositor (pure-qml and minimal-qml examples) started with :

• QT_WAYLAND_CLIENT_BUFFER_INTEGRATION=linux-dmabuf-unstable-v1
• QSG_RHI_BACKEND=vulkan
• QT_QPA_PLATFORM=vkkhrdisplay

Clients (also tried with non-Qt apps) started with :

• QSG_RHI_BACKEND=vulkan
• QT_QPA_PLATFORM=wayland

However, the clients run only when I also set VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/lvp_icd.x86_64.json (which mean using Lavapipe/LLVMPipe for the clients), or if the clients are run using the opengl RHI backend.

What I also find strange is the line "libEGL debug: MESA-LOADER: dlopen(/usr/lib/dri/swrast_dri.so)" in the logs of clients (below, the gallery QtQuick Controls example).

If I set the MESA_LOADER_DRIVER_OVERRIDE variable to "zink", then the output becomes "libEGL debug: MESA-LOADER: dlopen(/usr/lib/dri/zink_dri.so)", but it does not seem to change anything. If I set its value to "radeonsi" or "v3d" (tried on a laptop and a rpi4), then the output remains "libEGL debug: MESA-LOADER: dlopen(/usr/lib/dri/swrast_dri.so)".