[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
Mon Mar 19 14:47:06 CET 2018

hi Laszlo,

thanx for the prompt reply, here the bug filed:


i'll continue my investigation too, let's hope to sort out something.

i'm wondering if there's a reason why the "widgets" are less used in 
multi-screen setups. i supposed they were "first class citizens" of the 
Qt Stack.

BTW if the issue is that they are typically "sw rendered"  only, that 
could be a problem for me too, because i was trying to "leverage" the 
OpenGL ES HW core in the A20 SOC to reduce CPU usage in a high refresh 
rate app! :-|

anyway in my first tests with Wayland&Weston the same app was seeing a 
huge relief (in terms of CPU load) then running as "Mesa3d" sw rendering 
on the Linux simplefb. that's why i was hopefull!

On 03/19/2018 02:20 PM, Laszlo Agocs wrote:
> Hi,
> 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,
> Laszlo
> *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
> hello,
> 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:
> https://github.com/aventuri/widgetMultiScreen
> the outcome is the wrong display of the two (yellow and red) 
> rectangles with the code above only on the ext HDMI diplay. see:
> https://drive.google.com/open?id=1tGJxoBzBNn_wEhCi5mnI5a5zLSKIrAwX
> the puzzling issue is that if i comment out the w2.show() line:
> https://github.com/aventuri/widgetMultiScreen/blob/master/main.cpp#L3
> 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:
>     Hi,
>     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,
>     Laszlo

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