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

Laszlo Agocs laszlo.agocs at qt.io
Mon Mar 19 14:20:37 CET 2018


No immediate ideas unfortunately, but it could well be that widgets (raster windows) do not behave as well in this regard as pure OpenGL windows (Qt Quick and friends). The multi-head work in the past was focused on the latter.

Please create a bug report at https://bugreports.qt.io

Best regards,

From: Interest <interest-bounces+laszlo.agocs=qt.io at qt-project.org> On Behalf Of Andrea Venturi
Sent: mandag 19. mars 2018 12.32
To: interest at qt-project.org
Subject: Re: [Interest] issues with Qt 5.9.3 with eglfs QPA_Platform on DRM/KMS kernel on Arm32/Mali HW


i put together a small code snippet for QtCreator, to better showcase the issue i see in my dual-head setup with a Qt widget app running through EGLFS on a libMali.so/DRM/KMS setup on Allwinner A20 mainline based OS:


the outcome is the wrong display of the two (yellow and red) rectangles with the code above only on the ext HDMI diplay. see:


the puzzling issue is that if i comment out the w2.show() line:


i can see (correctly) a single yellow screen on the primary LCD display.

can someone point me toward better debugging? is a GDB step by step approach the best one?  the Qt stack is that huge..

On 03/09/2018 02:42 PM, Laszlo Agocs wrote:


eglfs_mali is for Mali userspace drivers (https://developer.arm.com/products/software/mali-drivers/user-space) marked as fbdev. This is from the time when there were only two options, fbdev and x11.

When having the wayland variants in place, use eglfs_kms instead. When in doubt, try running weston first. If it comes up correctly, eglfs_kms is the right choice. This has been tested with an Asus Tinkerboard (Rockchip RK3288) a while ago. I don’t have experience with other Mali-based boards.

We do have multi-screen support with DRM, yes. The fbdev and other backends have none or very limited capabilities in this regard. The way forward is to use eglfs_kms (or eglfs_kms_egldevice when on NVIDIA) whenever possible.

Best regards,

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