[Interest] issues with Qt 5.9.3 with eglfs QPA_Platform on DRM/KMS kernel on Arm32/Mali HW

Andrea Venturi ennesimamail.av at gmail.com
Fri Mar 9 13:00:19 CET 2018

hello guys,

the subject says a lot.. :-) let me extend a bit in the body, anyway!

i'm working on a buildroot based OS on top of a Allwinner A20 based EVB
(Olimex A20 SOM) with both a LCD and an HDMI interface.

with a fairly latest 4.15 kernel and proper DTS i can see kmstest showing
correctly two test cards on both heads/screens. so far so good

now i'd like to use the Mali acceleration for snappy Qt experience (two
apps each running full screen on its head..); i know the libMali.so is a
bit of a mess and i currently use this binary blobs:


AFAIK it's ARM32 release for "allwinner gears". and it currently someway
works on wayland but it's bit too heavy for my workload.

i'm wondering if that trunk is good also for "lighter" gbm-only approach
(wayland free.. i mean)

i'm trying to make Qt5 use the eglfs backend, because i suppose the less
the code, the less the bugs.. :-)

but i fail to understand if i have to use elgfs_mali or eglfs_kms device
integration, because the first one failt on "createdisplay()" with a
segfault inside the libMali.so binary blob.

i'm wondering if this issue is related to the fact that the Mali
integration in qt5 eglfs is supposed to use /dev/fb0 for video mode
setting, but the dual head DRM/KMS setup is not offering a complete
dual-head fbdev emulation (and never will AFAICS from the linux-sunxi

so my question is, finally, is the eglfs_kms supposed to be able to:

* drive correctly the dual-head DRM/KMS setup
* still use the libGLESV2 accelerated path provided by libMali.so

if the latter is true, i'm wondering what's the purpose of eglfs_mali
"device integration".. is that a leftover of times where only /dev/fbX mode
setting was supported?

what's the long term more healthy path to support acceleration and
dual/multiple heads on linux mainline?

really let me know if there are reference updated documentation with clear
information of the different implementation and their use cases, because my
google-fu is failing on me and i find a lot of discussions dealing with
Mali (on many different SOCs) with very few technical details and insights
(that's why this post is pretty long.. feel free to ask for more info if
i'm missing something usefull).


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